REFERENCES OF PAPERS ON CODED MASK IMAGING AND RELATED SUBJECTS
Status: April 14, 1995
Prepared by:
Jean in 't Zand (Los Alamos National Lab, NM, USA),
Gerry Skinner (University of Birmingham, UK),
Rob Rideout (University of Birmingham, UK)
The following list concerns 296 papers that deal with the principle and
details of coded aperture imaging (i.e., aperture designs, camera
configurations, reconstruction designs and related subjects), as well
as have sideways references to coded aperture imaging.
If you have a preprint of a paper on coded-aperture imaging,
I'd appreciate
it very much if you send me a copy!
Ables, J.G.: 1968, Proceedings of the Astronomical Society of Australia, 1,172
Fourier Transform Photography: A New Method for X-Ray Astronomy
In comparison with all other branches of astronomy, X-ray astronomy suffers from
a relative dearth of image forming devices. No X-ray lens is known and image
formation by reflection requires glancing incidence optics which have small
fields of view and are extremely difficult to fabricate, even for small
apertures (about 2 cm;2) now employed. The only other imaging device which has
been successfully employed is the simplest of all, the pinhole camera. Pinhole
cameras with resolutions better than 10;-3~rad are easily constructed, but the
apertures are very small--not greater than about 10;-4 cm;2. The new instrument
described here is closely related to the pinhole camera and may be viewed as an
attempt to overcome the aperture restrictions of this simple device.
Aitken, G.J.M.,Corteggiani, J.P.,Gay, J.: 1981, Journal of the Optical Society
of America, 71,759
Partially Redundant Apertures for Infrared Stellar Imaging
Akimov, V.V.,Blokhintsev, I.D.,Leikov, N.G.: 1988, Space Science Reviews, 49,
139
Characteristics of the Telescope Gamma-1 in the Coded Aperture Mode
Antweiler, M.,Bomer, L.: 1990, Electronics Letters, 26,2068
Merit Factor of Chu and Frank Sequences
Antweiler, M.,Bomer, L.: 1991, Electronics Letters, 27,777
Merit Factor of Chu and Frank Sequences - Reply
Antweiler, M.F.M.,Bomer, L.,Luke, H.D.: 1990, IEEE Transactions On Information
Theory, 36,696
Perfect Ternary Arrays
Antweiler, M.,Luke, H.D.: 1994, Frequenz, 48,58
Mismatched Filtering for Periodical Binary Arrays
The crosscorrelation function of a two-dimensional binary array with a
mismatched filter array is an ideal impulselike signal. A measure for the loss
of the signal-to-noise ratio compared to matched filtering is the filter
efficiency of the binary array. The paper derives three methods for the
construction of binary arrays with a high filter efficiency. Furthermore, a
method for searching the best binary arrays with certain dimensions is
introduced. Two tables comprise the best results obtained by the search and
constructive methods for arrays with up to 40 and 256 elements, respectively.
Applications of the arrays lie in the field of two-dimensional signal
processing, e.g. group coding or coded aperture imaging.
Arefev, V.A.,Bugrov, V.P.,Volchanskii, A.V.,Gurov, A.Y.,Korotkova, E.V.,Perkov,
A.I.,Fedotov, S.N.,Sharak, M.P.: 1990, Instruments and Experimental Techniques,
33,776
Gamma-Telescope With One-Dimensional Coded Aperture
A one-dimensional scintillation gamma telescope with a coded aperture is
described that permits real-time monitoring of the space-energy distributions of
gamma sources with energies of 0.5-5 MeV. The telescope has an angular
resolution of 1.9-degrees-3.2-degrees and an arc of vision of 26-degrees-50-
degrees.
Badiali, M.,Cardini, D.,Emanuele, A.,Ranieri, M.,Soggiu, E.: 1985, Astronomy and
Astrophysics, 151,259
Hard X-Ray-Imaging With a Rotating Wide Field Coded Mask Telescope - An Inflight
Test
Barber, H.B.,Barrett, H.H.,Wild, W.J.,Woolfenden, J.M.: 1983, Journal of Nuclear
Medicine, 24,P25
Development of Small Gamma-Ray Imaging Probes for Invivo Use
Barret, D.,Laurent, P.: 1991, Nuclear Instruments & Methods in Physics Research
Section A-Accelerators Spectrometers Detectors and Associated Equipment, 307,
512
Calibration of Detectors for Soft Gamma-Ray Astronomy - The Monte-Carlo Approach
Applied to the Sigma-Telescope
The general problem of calibrating soft gamma-ray (100 keV-1 MeV) detectors is
illustrated in the case of the SIGMA experiment. Particularly, the advantage of
coded mask experiments for spectroscopy and the related specific calibration
difficulties are considered. It is shown that a Monte Carlo simulation can
separate in the spectrum the components due to the experiment itself and those
due to the scattering in the environment and permits to take into account
experimental configuration modifications after the calibrations. A very detailed
geometrical description of the SIGMA telescope is proposed and its in-flight
energy response is estimated from Monte Carlo simulations.
Barrett, H.H.,DeMeester, G.D.: 1974, Applied Optics, 13,1100
Quantum Noise in Fresnel Zone Plate Imaging
A Fresnel zone plate, used as a coded aperture, offers a great advantage in
geometric collection efficiency over a conventional pinhole or collimator. We
present a detailed analysis of the signla-to-noise ratio (SNR) of a quantum-
limited zone plate camera. The magnitude and spatial distribution of the noise
field and its dependence on the source distribution and the characteristics of
the optical processing system are derived. It is shown that the largest SNR
advantage occurs for a point source, while for very large, uniform sources there
may be a slight net disadvantage using a zone plate. It is also shown that
optical processing does not give the highest possible SNR.
Barrett, H.H.,Horrigan, F.A.: 1973, Applied Optics, 12,2686
Fresnel Zone Plate Imaging of Gamma Rays; Theory
The use of a Fresnel zone plate as a coded aperture for imaging incoherent
radiation such as gamma rays has been previously reported. The coded image is in
many respects similar to a hologram and can be decoded or reconstructed with a
coherent optical system. In this paper, the general theory of coded-aperture
imaging is presented, first for an arbitrary code and the for an on-axis zone
plate, an off-axis zone plate, and a one-dimensional zone plate (or linear
chirp). With the on-axis plate, a matched imaging condition is suggested as a
guide to optimizing image contrast. With the off-axis zone plate and the linear
chirp, it is necessary to use a half-tone screen to spatially heterodyne the
object spectrum into the passband of the aperture. In all three cases,
expressions for the resolution, depth of field, field of view and relative
efficiency are derived. A simplified noise analysis is presented, and some
practical system constraints are discussed.
Bassani, L.,Butler, R.C.,Caroli, E.,Dicocco, G.,Natalucci, L.,Spizzichino, A.,
Stephen, J.B.: 1989, Astrophysical Letters & Communications, 27,321
Simulated Observations of Low-Energy Gamma-Ray Sources
A series of Monte-Carlo simulated observations of gamma ray sources has been
obtained for the Zebra telescope, using recent observational data. The results
of the simulations are analyzed in order to assess both the sensitivity and
imaging capability of the instrument during a typical balloon flight. It is
shown that sources like the Crab nebula, the quasar 3C273, and the Seyfert
galaxy NGC4151 will be observable over the entire energy range of the instrument
(0.2-10 MeV) at the few tens of sigma confidence level and will be located with
an accuracy of the order of a few arcminutes. Furthermore, the simulations
furnish an estimate of the capability of the telescope to resolve complex
structured sources such as SS433 or crowded regions of the sky like that of the
Galactic Center.
Bedrosian, S.D.: 1986, Proceedings of the IEEE, 74,1040
Nonuniform Linear Arrays - Graph-Theoretic Approach to Minimum Redundancy
Bignami, G.F.,Dean, A.J.,Durouchoux, P.,Hurley, K.,Lund, N.,McBreen, B.,
Schonfelder, V.,Swanenburg, B.N.,Tomaschek, G.,Winkler, C.: 1988, Space Science
Reviews, 49,157
The GRASP Telescope
Bignami, G.F.,Dean, A.J.,Durouchoux, P.,Lund, N.,McBreen, B.,Ramsden, D.,
Staubert, R.,Taylor, B.G.,Vedrenne, G.: 1987, IEEE Transactions On Nuclear
Science, 34,31
GRASP - Gamma-Ray Astronomy With Spectroscopy and Positioning
Boella, G.,Bussini, A.,Butler, R.C.,Caroli, E.,Caralambous, P.M.,Dean, A.J.,
Dicocco, G.,Donati, S.,Graham, G.,Holder, S.M.,Mastropietro, M.,Perotti, F.,
Santambrogio, R.,Traci, S.,Ubertini, P.,Villa, G.,Younis, F.A.: 1986, IEEE
Transactions On Nuclear Science, 33,755
The Basic Unit of the Imaging Plane of the Zebra Low-Energy Gamma-Ray Telescope
Bomer, L.,Antweiler, M.: 1990, IEEE Transactions On Information Theory, 36,411
2-Dimensional Perfect Binary Arrays With 64 Elements
Bomer, L.,Antweiler, M.: 1993, Signal Processing, 30,1
Optimizing the Aperiodic Merit Factor of Binary Arrays
The merit factor of an array specifies the ratio of the energy of its
autocorrelation function mainlobe to the energy of its autocorrelation function
sidelobes. The merit factor of both the periodic and the aperiodic
autocorrelaton function of binary arrays is investigated. The merit factor for
the periodic autocorrelation function is computed for known classes of binary
arrays, such as perfect arrays, shift-register arrays, Legendre arrays, Calabro-
Wolf arrays, Lempel arrays, difference set arrays and product arrays. By
applying invariance operations to these arrays, the merit factor of the
aperiodic autocorrelation function is increased and the sidelobes of the
aperiodic autocorrelation function are decreased. The resulting maximal merit
factors and minimal sidelobes are tabulated.
Bomer, L.,Antweiler, M.,Schotten, H.: 1993, Frequenz, 47,190
Quadratic Residue Arrays
In this paper, a new construction method for synthesizing two- and higher-
dimensional quadratic residue arrays is introduced. The construction is mainly
based on addressing the elements of an m-dimensional array by the elements of
Galois Field GF(p(m)), where p denotes an odd prime and m denotes an integer.
With a following mapping, the elements of the m-dimensional array, except the
leading element, are set to either + 1 or - 1. The dimensions of the resulting
m-dimensional arrays have the size p. It is shown that the periodic
autocorrelation function of these quadratic residue arrays are two- or three-
level, depending on whether the number of elements is N = 1 mod 4 or N = 3 mod
4. With these quadratic residue arrays, new classes of two- and higher-
dimensional pseudonoise and Legendre arrays are obtained.
Borozdin, K.,Gilfanov, M.,Syunyaev, R.,Churazov, E.,Loznikov, V.,Yamburenko, N.,
Skinner, G.K.,Patterson, T.G.,Willmore, A.P.,Emam, O.,Brinkman, A.C.,Heise, J.,
In 't Zand, J.J.M.,Jager, R.: 1990, Soviet Astronomy Letters, 16,804
KS1947+300 - A New Transient-X-Ray Source in Cygnus
While observing the transient x-ray source GS 2023 + 338 on June 1989 with the
TTM telescope aboard the Kvant module on the Mir space station, we detected a
new transient source, KS 1947 + 300 (Skinner, 1989). On the first day it was
observed, the flux from this object in the 2-27 keV band was 70 +/- 10 mCrab.
The flux subsequently declined, and on 19 August, the 3-sigma upper limit on the
flux was 10 mCrab.
Braga, J.,Covault, C.E.,Grindlay, J.E.: 1989, IEEE Transactions On Nuclear
Science, 36,871
Calibration and Performance of the Energetic X-Ray-Imaging Telescope Experiment
Braga, J.,Covault, C.E.,Manandhar, R.,Grindlay, J.E.: 1990, Revista Mexicana De
Astronomia Y Astrofisica, 21,633
Hard X-Ray Arcmin Imaging With the EXITE Telescope
In this paper we describe the Energetic X-ray Imaging Telescope Experiment
(EXITE) and show the first results obtained. We discuss the coded-aperture
technique for imaging of cosmic X-ray sources, used by EXITE.
Braga, J.,Villela, T.,Jayanthi, U.B.,D'Amico, F.,Neri, J.A.: 1991, Experimental
Astronomy, 2,101
A New Mask-Antimask Coded-Aperture Telescope for Hard X-Ray Astronomy
A new imaging balloon-borne telescope for hard X-rays in the energy range from
30 to 100 keV is described. The imaging capability is provided by the use of an
extended URA-based coded mask. With only one motor and suitable stop bins, we
can rotate a carbon-fibre wheel with most of the mask elements attached to it by
180 deg, and a bar, which is also part of the mask pattern and is allowed to
rotate freely over the wheel, by 90 deg; this combined rotation creates an
antimask of the original mask, except for the central element. This is a novel
and elegant manner of providing an antimask without additional weight and
complex mechanical manipulations. We show that the use of antimasks is a very
effective method of eliminating systematic variations in the background map over
the position sensitive detector area. The expected sensitivity of the instrument
for the 30-100 keV range is of the order of 7X10;-5 photons cm;-2 s;-1 keV;-1,
for an integration time of 10;4 seconds at a residual atmosphere of 3.5 g cm;-2.
This telescope will provide imaging observations of bright galactic hard X-ray
sources with an angular resolution of ~2 deg. in a 10 deg by 10 deg FOV, which
is defined by a collimator placed in front of the detector system. We are
particularly interested in the galactic center region, where recent imaging
results in X-rays have shown the presence of an interesting source field.
Results of computer simulations of the imaging system are reported.
Brown, C.M.: 1972, Ph.D. Thesis, University of Chicago
Multiplex Imaging With Random Arrays
The signal-to-noise ratio in the image from a pinhole camera can be improved by
replacing the single pinhole with many pinholes. Pictures from such cameras are
subjected to a posteriori interpretation (postprocessing) which collects the
images from all the pinholes into a single, stronger image. When the images from
individual pinholes overlap on the film, we say they are multiplexed; advantages
can then accrue both from better utilization of information gathering and
storage resources and from nonlinear detector response. While the latter effect
is best explored experimentally, the linear phenomena in such a system may be
treated theoretically. The system is an example of a multiplexing system using
correlation coding and decoding methods. Multiplexing systems have in common the
goal of increasing the rate in a noisy channel by sending through it a
superposition of several encoded messages. The imaging process is equivalent to
encoding and decoding messages by correlation with binary arrays. In the absence
of a priori information about the messages to be sent, this coding can induce a
loss of information, an uncertainty inherent to the technique. Promising methods
for synthesis of code arrays inducing low uncertainty are reviewed, and no
better two-dimensional codes are found for aperiodic correlation than random
arrays whose characteristics have been improved slightly by iterative methods.
In the imaging application, the coding induces uncertainty in the form of two
kinds of intensity inaccuracies: one of low and one of high spatial frequency.
The usual postprocessing technique (optical matched filtering) is unsatisfactory
in multiplexing systems. Although it has some optimal noise-rejection
properties, in multiplexing it can cause an unacceptable amount of low spatial
frequency inaccuracy. Two new postporcessing schemes are introduced (mismatched
filtering and pseudomatched filtering involving image subtraction) which can
remove this low spatial frequency inaccuracy, at the same time lessening the
inaccuracies of high spatial frequency. Detailed models of the inherent
uncertainty are developed for the three postprocessing schemes. The uncertainty
produced by correlation coding methods is modelled as a quasi- statistical nosie
process whose amplitude is proportional to the signal strength. Two common
physical processes, proportional to the square root of the signal and
independent of the signal, are mentioned and their effects evaluated. The most
promising coding schemes (nonmultiplexing, aperiodic correlation coding,
psuedoperiodic correlation coding with multiplexing) are compared using an
expression which includes the effects from all the noise processes. The
conditions are found under which each scheme is to be preferred. Multiplexing is
known to yield and advantage if signal-independent noise is dominant; it is
found that in the imaging system, multiplexing can yield an advantage even if
other forms of noise are dominant. Technniques are illustrated and qualitative
and quantitative predictions of the theory are tested.
Brown, C.: 1974, Journal of Applied Physics, 45,1806
Multiplex Imaging With Multiple-Pinhole Cameras
When making photographs in x rays or gamma rays with a multiple-pinhole camera,
the individual images of an extended object such as the sun may be allowed to
overlap; then the situation is in many ways analogous to that in a multiplexing
device such as a Fourier spectroscope. Some advantages and problems arising with
such use of the camera are discussed, and expressions are derived to describe
the relative efficacy of three exposure/postprocessing schemes using multiple-
pinhole cameras.
Brunol, J.,de Beaucoudrey, N.,Fonroget, J.: 1979, Optics Communications, 29,31
Sur La Statistique Et L'imagerie Dans Les Processus De Poission Codes
Bidimensionnel: Application a L'imagerie Nucleaire
Butler, R.C.,Caroli, E.,Dicocco, G.,Maggioli, P.P.,Spizzichino, A.,Charalambous,
P.M.,Dean, A.J.,Drane, M.,Gil, A.,Stephen, J.B.,Perotti, F.,Villa, G.,Badiali,
M.,Lapadula, C.,Polcaro, F.,Ubertini, P.: 1984, Nuclear Instruments & Methods in
Physics Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 221,41
An Evaluation of the Background Introduced from the Coded Aperture Mask in the
Low-Energy Gamma-Ray Telescope Zebra
The background which arises from the presence of a coded aperture mask is
evaluated. The major contributions which have been considered here are the
interactions with the mask of the isotropic gamma ray background, a parallel
gamma ray beam, neutrons and the effect of the mask element profile. It is shown
that none of these factors contribute to a significant excess or modulation in
the background counting rate over the detection plane. In this way the use of a
passive rather than an active coded aperture mask is seen to be suitable for use
in a low energy gamma ray telescope.
Byard, K.: 1992, Nuclear Instruments & Methods in Physics Research Section A-
Accelerators Spectrometers Detectors and Associated Equipment, 322,97
On Self-Supporting Coded Aperture Arrays
Two new constructions for fully self-supporting coded aperture arrays are
presented, which produce apertures having equivalent imaging properties to those
of the pseudo noise product (PNP) arrays. These two constructions, called the M-
P and M-M constructions, increase the number of available self-supporting coded
aperture patterns by between 80% and 187% for unit pattern orders up to 10000.
Byard, K.: 1992, Nuclear Instruments & Methods in Physics Research Section A-
Accelerators Spectrometers Detectors and Associated Equipment, 313,283
An Optimized Coded Aperture Imaging-System
A new coded aperture system design for use with circular detectors is discussed,
whereby square element coded aperture unit patterns are mosaiced onto a circular
detector with a view to maximising the size of the unambiguous field of view for
any given detector radius. The results for these optimum configurations are
presented for all 50% transparency URA and MURA unit patterns of order v < 600.
Improvements in the FOV size over standard rectangular mosaicing are presented
with the available increase being found to be around 23% for large values of v.
Byard, K.: 1992, Experimental Astronomy, 2,227
Square Element Antisymmetric Coded Apertures
This paper describes a method for constructing square element coded aperture
patterns which possess 90 deg antisymmetry. The resulting patterns now make
possible the removal of systematic detector background noise from a square pixel
detector by means of 'antimask' imaging using a single aperture, and without
requiring full 180 deg aperture rotation
Byard, K.: 1993, Electronics Letters, 29,2011
Family of Binary Sequences With Useful Correlation-Properties
A method for the synthesis of an infinite family of binary sequences with
perfectly flat cross-correlation sidelobes is presented. The corresponding
postprocessing arrays are similarly two-valued, and so the sequences may be
particularly suited to applications in high noise environments.
Byard, K.: 1993, Nuclear Instruments & Methods in Physics Research Section A-
Accelerators Spectrometers Detectors and Associated Equipment, 336,262
Synthesis of Binary Arrays With Perfect Correlation-Properties -Coded-Aperture
Imaging
A new method for the synthesis of binary arrays which have perfect cross-
correlation properties is presented. The arrays, which are discussed with an
emphasis on coded aperture imaging, may also be of use in a number of other
applications, including signal processing, telecommunications and radio antenna
design. The new coded aperture configurations which are made available offer a
wider choice of possible aperture parameters, and conveniently fill a gap in the
system parameters that are currently available. The increased freedom of system
choice, which can be made for both one- and two-dimensional systems, includes
the size of the aperture array and its throughput value. The new two-dimensional
apertures have the further advantage of being fully self-supporting.
Byard, K.,Dean, A.J.,Goldwurm, A.,Hall, C.J.,Harding, J.S.J.,Lei, F.: 1990,
Astronomy and Astrophysics, 227,634
Imaging Using HURA Coded Apertures With Discrete Pixel Detector Arrays
Hexagonal URA (HURA) coded apertures have important properties for gamma-ray
imaging and they have been successfully used in conjunction with an Anger camera
for astronomical gamma-ray observations. However, when coupled to a detector
plane constructed from discrete pixels an inherent systematic noise due to the
non-perfect overlap between mask elements and detector pixels can cause
degradation of the image quality. Here we presents the results of computer
simulations designed to evaluate the basic performance of a system employing a
rotating HURA mask and two discrete detector pixel geometries: a square pixel
detector (SPD) and a hexagonal pixel detector (HPD). Intrinsic systematic noise
has been found to affect the quality of the system point spread function for
both detector geometries. The noise varies with the mask orientation, the
detector resolution and the source position, and is highly magnified by the
background level. Special configurations for the HPD geometry have been
identified for which a nearly perfect overlap of mask elements with detector
pixels occurs at two mask orientations. Under these conditions the systematic
noise is completely absent.
Byard, K.,Ramsden, D.: 1994, Nuclear Instruments & Methods in Physics Research
Section A-Accelerators Spectrometers Detectors and Associated Equipment, 342,
600
Coded-Aperture Imaging Using Imperfect Detector Systems
The imaging properties of a gamma-ray telescope which employs a coded aperture
in conjunction with a modular detection plane has been investigated. Gaps in the
detection plane, which arise as a consequence of the design of the position
sensitive detector used, produce artifacts in the deconvolved images which
reduce the signal to noise ratio for the detection of point sources. The
application of an iterative image processing algorithm is shown to restore the
image quality to that expected from an ideal detector. The efficiency of image
processing has enabled its subsequent application to a general coded aperture
system in order to gain a significant improvement in the field of view without
compromising the angular resolution.
Cannon, T.M.,Fenimore, E.E.: 1978, IEEE Transaactions On Nuclear Science, NS-25,
184
A Class of Near Perfect Coded Apertures
Cannon, T.M.,Fenimore, E.E.: 1979, Applied Optics, 18,1052
Tomographical Imaging Using Uniformly Redundant Arrays
No abstract
Cardini, D.,Badiali, M.,Emanuele, A.,Farina, G.,Gianni, G.,Ranieri, M.,Catanesi,
M.G.,Maggi, G.,Selvaggi, G.,Waldner, F.: 1983, Astronomy and Astrophysics, 127,
169
A Hard X-Ray-Imaging Experiment Using a Coded Mask Telescope Prototype
Caroli, E.,Butler, R.C.,Di Cocco, G.,Maggioli, P.P.,Natalucci, L.,Spizzichino,
A.: 1984, Il Nuovo Cimento, 7,786
Coded Masks in X- And Gamma-Ray Astronomy: The Problem of the Signal-To-Noise
Ratio Evaluation
Coded-mask telescopes are presently considered as one of the best solutions for
producing images of the sky in hard X-ray and gamma-ray astronomy, because they
can posses optimum signal-to-noise ratio (SNR), which is crucial in an energy
range in which the expected fluxes are generally low compared with the
background. For a given field of the sky, the values of the SNR, associated with
each pixel of the reconstructed image, depend on both the mask design and the
decoding technique employed. The expressions for the SNR of a variety of
replicated masks are derived for the cases of the inversion and the correlation
methods, in different conditions of background and source fluxes. For the
inversion method, the SNR is found to be simply inversely proportional to the
square root of the trace of the matrix associated with the mask, but generally
in the case of the correlation method the SNR is limited by an additional
systematic term due to the cross-talk between sources in the field of view. The
effect of this term can be avoided by choosing a uniformly redundant array
pattern.
Caroli, E.,Stephen, J.B.,Di Cocco, G.,Natalucci, L.,Spizzichino, A.: 1987, Space
Science Reviews, 45,349
Coded Aperture Imaging in X- And Gamma-Ray Astronomy
Coded aperture imaging in high energy astronomy represents an important
technical advance in instrumentation over the full energy range over X-rays till
gamma-rays and is playing a unique role in those spectral ranges where other
techniques become ineffective or impracticable due to limitations connected to
the physics of interactions of photons with matter. The theory underlying this
method of indirect imaging is of strong relevance both in design optimization of
new instruments and in the data analysis process. The coded aperture imaging
method is herein reviewed with emphasis on topics of mainly practicle interest
along with a description of already developed and forthcoming implementations.
Carter, J.N.,Charalambous, P.,Dean, A.J.,Stephen, J.B.,Butler, R.C.,Dicocco, G.,
Morelli, E.,Spada, G.,Spizzichino, A.,Barbareschi, L.,Boella, G.,Perotti, F.,
Villa, G.,Badiali, M.,Lapadula, C.,Polcaro, F.,Ubertini, P.: 1982, Nuclear
Instruments & Methods in Physics Research, 196,477
A Position-Sensitive Detector for a Gamma-Ray Imaging Telescope
Carter, J.N.,Ramsden, D.,Frye, G.M.,Jenkins, T.L.,Koga, R.: 1982, Monthly
Notices of the Royal Astronomical Society, 198,33
High-Resolution Gamma-Ray Telescope Using a Coded Aperture Mask and Drift
Chamber
Charalambous, P.M.,Dean, A.J.,Engel, A.R.,Simnett, G.: 1984, Proceedings of the
Society of Photo-Optical Instrumentation Engineers, 445,394
An Imaging Telescope for Gamma-Ray Astronomy - Tigar
Charalambous, P.M.,Dean, A.J.,Stephen, J.B.,Young, N.G.S.: 1984, Applied Optics,
23,4118
Aberrations in Gamma-Ray Coded Aperture Imaging
Laboratory test have been performed to investigate the quality of gamma-ray
images which may be obtained using the coded aperture mask technique. A number
of potential sources of image defects are examined both theoretically and
experimentally, and the methods in which these may be minimized eliminated are
studied. It is shown that good quality gamma-ray images may be produced by
efficient design and control of the imaging system.
Charalambous, P.M.,Dean, A.J.,Stephen, J.B.,Young, N.G.S.,Gourlay, A.R.: 1984,
Nuclear Instruments & Methods in Physics Research Section A-Accelerators
Spectrometers Detectors and Associated Equipment, 221,56
Aberrations in Gamma-Ray Imaging-Systems
The aberrations present in a coded aperture imaging system have a fundamentally
different origin to those found in a focused optical instrument. A series of
laboratory tests is described in which masks with carefully controlled defects
were employed to generate non-perfect gamma-ray images, so that the magnitude of
the aberrations introduced could be quantitively investigated. The results of
these test are presented and the extend to which they affect the design of a
practical gamma-ray imaging system is discussed.
Chen, Y.W.,Miyanaga, N.,Yamanaka, M.,Nakai, M.,Tanaka, K.,Nishihara, K.,
Yamanaka, T.,Nakai, S.: 1990, Journal of Applied Physics, 68,1483
3-Dimensional Imaging of Laser Imploded Targets
Chen, Y.W.,Yamanaka, M.,Miyanaga, N.,Azechi, H.,Ishikawa, S.,Yamanaka, T.,Nakai,
S.,Tamura, S.: 1989, Optics Communications, 73,337
Measurement of D-D Burn Region Using Proton Penumbral Coded Aperture Imaging
Chen, Y.W.,Yamanaka, M.,Miyanaga, N.,Yamanaka, T.,Nakai, S.,Yamanaka, C.,Tamura,
S.: 1989, Optics Communications, 71,249
3-Dimensional Reconstruction of Laser-Irradiated Targets Using URA Coded
Aperture Cameras
Chou, C.: 1984, Proceedings of the Society of Photo-Optical Instrumentation
Engineers, 454,457
Fourier Coded Aperture Imaging in Nuclear-Medicine
Chou, C.: 1994, IEE Proceedings-Science Measurement and Technology, 141,179
Fourier Coded-Aperture Imaging in Nuclear-Medicine
A Fourier aperture (FA) is composed of two sinusoidal gratings in contact. When
the two gratings rotate on the same axis in equal angles but opposite directions
a clear pattern of difference moire fringes is formed, the moire frequency
depending on the angle between the two gratings. This aperture of moire fringes
is used as a variable frequency grating which is able to scan the object
spectrum in the frequency domain. The summation-filtered back projection
algorithm with three different apodising functions was introduced in the
reconstruction. A Tc-99m gamma ray source and a 1 in-diameter NaI scintillation
detector were used in the experiment. The thyroid phantom images showed that
spatial resolution of FA agrees with the theoretical prediction. Three
dimensional image capability is also discussed. The matrix inversion algorithm
was used in the computer simulation of 3-D images. Although the depth resolution
of a FA is limited by the restricted view angle of the detector, two plane
objects free from noise at different depths were reconstructed.
Chou, C.,King, H.J.: 1984, Proceedings of the Society of Photo-Optical
Instrumentation Engineers, 454,465
Gamma-Ray Imaging By Single Grating Aperture
Chou, C.,King, H.J.: 1994, Japanese Journal of Applied Physics Part 1-Regular
Papers Short Notes & Review Papers, 33,2072
Quantum-Noise of Fourier-Coded Aperture Imaging-System
The single-grating aperture (SGA) and Fourier aperture (FA) both behave as
variable frequency gratings to record the object spectrum directly in a Fourier
domain when quantum noise is originally generated in this region. This is in
contrast to a stationary coded aperture in which the noise appears in the space
domain in the shadow-casting images. The noise properties of SGA and FA imaging
systems, using the summation filtered backprojection reconstruction algorithm,
have been determined. They are proportional to the square root of the intensity
distribution of the object. From the theoretical calculations, signal-to-noise
ratios of SGA and FA show the same performance as the SNR of a pinhole camera
for small objects. However, for larger objects, SGA and FA show better
performance than the pinhole camera. The calculated SNRs of a point and a disc
object agree with the experimental results.
Cook, W.R.,Finger, M.,Prince, T.A.,Stone, E.C.: 1984, IEEE Transactions On
Nuclear Science, 31,771
Gamma-Ray Imaging With a Rotating Hexagonal Uniformly Redundant Array
Cook, W.R.,Grunsfeld, J.M.,Heindl, W.A.,Palmer, D.M.,Prince, T.A.,Schindler,
S.M.,Stone, E.C.: 1991, Astrophysical Journal, 372,L75
Coded-Aperture Imaging of the Galactic-Center Region At Gamma-Ray Energies
The first coded-aperture images of the Galactic center region at energies above
30 keV have revealed two strong gamma-ray sources. One source has been
identified with the X-ray source 1E 1740.7-2942, located 0.8-degrees away from
the nucleus. If this source is at the distance of the Galactic center, it is one
of the most luminous objects in the galaxy at energies from 35 to 200 keV. The
second source is consistent in location with the X-ray source GX 354 + 0 (MXB
1728-34). In addition, gamma-ray flux from the location of GX 1 + 4 was
marginally detected at a level consistent with other post-1980 measurements. No
significant hard X-ray or gamma-ray flux was detected from the direction of the
Galactic nucleus (Sgr A*), or from the direction of the recently discovered
gamma-ray source GRS 1758-258.
Cook, W.R.,Palmer, D.M.,Prince, T.A.,Schindler, S.M.,Starr, C.H.,Stone, E.C.:
1988, Astrophysical Journal, 334,L87
An Imaging Observation of SN1987a At Gamma-Ray Energies
Cook, W.R.,Palmer, D.M.,Prince, T.A.,Schindler, S.M.,Starr, C.H.,Stone, E.C.:
1989, IAU Symposia,,581
Gamma-Ray Imaging of the Galactic-Center Region
Cordier, B.,Paul, J.,Mandrou, P.,Roques, J.P.: 1994, Nature, 368,698
Earth Occultation or Coded Mask
Covault, C.E.,Grindlay, J.E.,Manandhar, R.P.: 1992, Astrophysical Journal, 388,
L65
Hard X-Ray-Imaging of the Galactic Black-Hole Candidate GX339-4
Imaging and spectral observations in the energy range 20-250 keV of the black
hole candidate GX 339-4 have been obtained with the Energetic X-ray Imaging
Telescope Experiment (EXITE). Observations were made during a balloon flight
from Alice Springs, Australia on UT 1989 May 8-10. A single source of nearly 6-
sigma significance is detected near the center of the 3.4-degrees field of view
with a position consistent with GX 339-4. This is the first imaging observation
of GX 339-4 at hard X-ray energies. Our result confirms previously reported
results from nonimaging experiments showing significant hard X-ray flux up to
greater-than-or-similar-to 60 keV, with a power-law spectral fit similar to
other black hole candidates such as Cygnus X-1. The source may have been in an
outburst state similar to that recently detected with BATSE on GRO.
Covault, C.E.,Grindlay, J.E.,Manandhar, R.P.,Braga, J.: 1991, IEEE Transactions
On Nuclear Science, 38,591
Techniques for Removing Nonuniform Background in Coded-Aperture Imaging On the
Energetic X-Ray-Imaging Telescope Experiment
The coded-aperture technique for reconstructing images for a position-sensitive
detector looking through a stationary URA mask requires that the background
illumination be distributed uniformly across the surface of the detector. Non-
uniformities in the background are typical of balloon and space-borne detectors,
and introduce large artifacts into the reconstructed image, with a subsequent
loss of signal-to-noise. Here we describe a technique, employed for the
Energetic X-ray Imaging Telescope Experiment (EXITE) to remove the systematic
effects of non-uniform background. We explore the time dependence of intensity
and two-dimensional shape of the background detector image during the flight. We
construct a "flat field" image from observations where x-ray sources were absent
from the field of view. We demonstrate that this technique can successfully
reduce RMS fluctuations to within a few percent of ideal Poisson statistics.
Dallas, W.J.: 1979, Optics Communications, 30,155
Artifact-Free Region-Of-Interest Reconstruction from Coded Aperture Recordings
Dallas, W.J.,Linde, R.: 1983, Optica Acta, 30,1561
X-Ray Coded-Aperture Image-Reconstruction Using an Array of Kinoforms
Dean, A.J.,Badiali, M.,Chiappetti, L.,Caroli, E.,Court, A.,Dicocco, G.,Maggioli,
P.,Perotti, F.,Soggiu, E.,Spizzichino, A.,Stephen, J.B.,Ubertini, P.,Villa, G.,
Yearworth, M.: 1987, IEEE Transactions On Nuclear Science, 34,62
Laboratory Gamma-Ray Images Using the Zebra Telescope
Dicke, R.H.: 1968, Astrophysical Journal, 153,L101
Scatter-Hole Cameras for X-Rays and Gamma Rays
A pinhole camera for which the entrance area, covered with a very large number
of randomly distributed pinholes, is 50% open is shown to be a very effective
way of forming images of a complex of X-ray stars. A simple statistical trick is
used to reduce the multidunious overlapping images into a single image. Less
than forty detected photons are needed to form an image of a star.
Dicocco, G.,Butler, R.C.,Morelli, E.,Spada, G.,Spizzichino, A.,Villa, G.,
Barbareschi, L.,Boella, G.,Perotti, F.,Ubertini, P. (1981): The use of coded
aperture masks in low energy gamma-ray astronomy. In: Proceedings of the 17th
International Cosmic Ray Conference - Paris. Vol. 9. (: ) Commissariat a
l'Energie Atomique, Gif-sur-Yvette, France, 1-4.
(AE(CNR, Laboratorio di Tecnologie e Studio delle Radiazioni
Extraterrestri, Bologna, Italy) AI(CNR, Istituto de Fisica Cosmica, Milan,
Italy) AJ(CNR, Istituto di Astrofisica Spaziale, Frascati, Italy))
Ducros, G.,Ducros, R.: 1984, Nuclear Instruments & Methods in Physics Research
Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,49
Statistical-Analysis for Coded Aperture Gamma-Ray Telescope
We have developed a statistical analysis of the image recorded by a photon
sensitive detector associated with a coded mask for the French gamma ray
telescope SIGMA, in the energy range 20-2000 keV. The aperture of the telescope
is not limited to the size of the mask. In the first part, we describe the
principle of the image analysis based on the least squares method with a fit
function generated and tested term after term. The statistical test is performed
on the F distribution followed by the relative improvement of chi;2 when the fit
function has an additional term. The second part deals with digital processing
aspects: the adjustment on the method to reduce computation time, and the
analysis results of two simulated images.
Dunphy, P.P.,McConnell, M.L.,Owens, A.,Chupp, E.L.,Forrest, D.J.,Googins, J.:
1989, Nuclear Instruments & Methods in Physics Research Section A-Accelerators
Spectrometers Detectors and Associated Equipment, 274,362
A Balloon-Borne Coded Aperture Telescope for Low-Energy Gamma-Ray Astronomy
Durouchoux, P.,Bignami, G.,Dean, A.,Lund, N.,McBreen, B.,Schonfelder, V.,
Swanenburg, B.,Vedrenne, G.,Winkler, C.: 1989, IAU Symposia,,633
Mapping the Galactic-Center Region With GRASP
Dyer, S.A.,Harms, B.K.,Park, J.B.,Johnson, T.W.,Dyer, R.A.: 1989, Applied
Spectroscopy, 43,435
A Fast Spectrum-Recovery Method for Hadamard-Transform Spectrometers Having
Nonideal Masks
Ekstrom, M.P.,Woods, J.W. (1974): Application of digital image restoration in X-
ray astronomy. In: . (: ),, . (Proceedings EASCON '74; Electronics and Aerospace
Systems Convention, Washington, D.C.; 640-645; N)
(Lawrence Livermore National Lab., CA.)
Emanuele, A.,Badiali, M.,Cardini, D.,Ranieri, M.,Catanesi, M.G.,Maggi, G.,
Selvaggi, G.,Waldner, F.: 1984, Astronomy and Astrophysics, 132,33
Detection and Localization of a Hard X-Ray Solar-Burst With a Balloon-Borne
Coded Mask Telescope
Epstein, R.,Skupsky, S.: 1990, Journal of Applied Physics, 68,924
Anticipated Improvement in Laser-Beam Uniformity Using Distributed Phase Plates
With Quasirandom Patterns
Ervin, A.,Barrett, H.H.,Gindi, G.R.,Paxman, R.G.,Gmitro, A.F.,Giles, C.L.: 1982,
Journal of the Optical Society of America, 72,1803
Hybrid Coded-Aperture Pinhole Imaging-System for Nuclear-Medicine
(Rotating slit compared with pinhole)
Eyles, C.J.,Skinner, G.K.,Willmore, A.P.,Bertram, D.,Harper, P.K.S.,Herring,
J.R.H.,Ponman, T.J.: 1987, Journal of the British Interplanetary Society, 40,
159
Spacelab 2 Coded Mask X-Ray Telescope
The X-ray imaging telescope built by the University of Birmingham for flight on
the Spacelab 2 mission is described in detail. The instrument comprises dual
coded mask telescopes having angular resolutions of 3 and 12 arcmin and which
respond to X-rays with photon energies in the range 2. 5-30 keV. The telescopes
are mounted on an independent pointing system so that observations of targets of
interest can be made regardless of the Orbiter's attitude. An attitude
measurement system comprising a low light level TV camera and a 35 mm film
camera, both of which record the images of optical stars, and a gyro pack
enables the pointing direction of the telescopes to be determined to an accuracy
of approximately 30 arcsec. (Author abstract) 3 refs.
Eyles, C.J.,Watt, M.P.,Bertram, D.,Church, M.J.,Ponman, T.J.,Skinner, G.K.,
Willmore, A.P.: 1991, Astrophysical Journal, 376,23
The Distribution of Dark Matter in the Perseus Cluster
We report on the analysis of spatially resolved spectral images of the Perseus
cluster obtained with a coded-mask X-ray telescope flown as part of the Spacelab
2 mission. The data allow the temperature and density profiles of the
intracluster gas to be measured. From these the cluster potential and hence the
cluster mass as a function of radius can be traced. The results show that there
is significantly less dark matter in the cluster than implied by virial mass
estimates based on the galaxies. The mass-to-light ratio within 1.3h50 Mpc of
the cluster center is found to be approximately 100(M./L.). The dark matter is
more centrally condensed than the X-ray - emitting gas and probably more so than
the galaxies, contrary to expectations from most cosmogonic scenarios. We show
that the conclusions are rather robust and insensitive to different
parameterizations and assumptions about the X-ray structure and argue that they
favor models in which the dark matter is baryonic.
Fenimore, E.E.: 1978, Applied Optics, 17,3562
Coded Aperture Imaging: Predicted Performance of Uniformly Redundant Arrays
URA's have autocorrelation functions with perfectly flat sidelobes. The URA
combines the high transmission characteristics of the random array with the flat
sidelobe advantage of the non-redundant pinhole arrays. A general expression for
the SNR has been developed for the URA as a function of the type of object being
imaged and the design parameters of the aperture. The SNR expression is used to
obtain and expression for the optimum aperture transmission. Currently, the only
2-D URAs known have a transmission of 1/2. This, however, is not a severe
limitation because the use of the non-optimum transmission of 1/2 never causes a
reduction in the SNR of more than 30%. The predicted performance of the URA
system is compared to the images obtainable from a single pinhole camera.
Because the reconstructed image of the URA contains virtually uniform noise
regardless of the original object's structure, the improvement over the single
pinhole camera is much larger for the bright points than it is for the low
intensity points. For a detector with high background noise, the URA will always
give a much better image than the single pinhole camera regardless of the
structure of the object. In the case of a detector with low background noise,
the improvement of the URA relative to the single pinhole camera will have lower
limit of ~2f;-1/2, where f is the fraction of the field of view that is
uniformly filled with object.
Fenimore, E.E.: 1980, Applied Optics, 19,2465
Coded Aperture Imaging: The Modulation Transfer Function for Uniformly Redundant
Arrays
Coded aperture imaging uses many pinholes to increase the SNR for intrinsically
weak sources when the radiation can be neither reflected nor refracted.
Effectively, the signal is multiplexed onto an image and then decoded, often by
computer, to form a reconstructed image. We derive the modulation transfer
function (MTF) of such a system employing URAs. We show that the MTF of a URA
system is virtually the same as the MTF of an individual pinhole regardless of
the shape or size of the pinhole. Thus, only the location of the pinholes is
important for optimum multiplexing and decoding. The shape and the size of the
pinholes can then be selected based on other criteria. For example, one can
generate self-supporting patterns, useful for energies typically encountered in
the imaging of laser driven compressions or in soft X-ray astronomy. Such
patterns contain holes all of the same size, easing the etching or plating
fabrication efforts for the apertures. A new reconstruction method is introduced
called delta-decoding. It improves the resolution capabilities of a coded
aperture system ny mitigating a blur often introduced during the reconstruction
step.
Fenimore, E.E.: 1983, Applied Optics, 22,826
Large Symmetric Pi-Transformations for Hadamard Transforms
No abstract
Fenimore, E.E.: 1986, Applied Optics, 26,2760
Time-Resolved and Energy-Resolved Aperture Images With URA-Tagging
Coded aperture imaging with URAs is the standard technique for imaging above the
limit of grazing incident X-ray telescopes. It is an ideal technique for high-
energy astrophysics because it has a high throughput, excellent performance on
point sources, and the ability to simultaneously measure signal and background.
However, many sources of interest in high-energy astrophysics are time variable
or require detailed energy spectra. Until now, to obtain a single time (or
energy) sample, the photons from the particular time (or energy) interval must
be formed into an encoded pattern, then processed to obtain an image for that
sample. Therefore, massive computations are required to cover the entire time
and energy parameter space. We present a new method of coded aperture analysis
called URA-tagging, which provides time and/or energy resolved histories of
sources with known positions without using a correlation operation. It can
easily reduce the computation time by orders of magnitude compared to the next
fastest method, the fast delta Hadamard transform. URA-tagging can also correct
for improperly encoded images or motion blurred images. Whereas previous methods
for quantifying performance have not taken into account the finite resolution or
the quantized sampling, URA-tagging provides a SNR equation that includes all
such effects. URA-tagging analysis explains why delta-decoding has a somewhat
poorer SNR than balanced correlation: naively, one would expect the better
resolution to yield a better SNR. In addition, we show that complementary URAs
(exchanged opaque and transparent elements) have different properties, and those
with an even number of transparent elements should be preferred.
Fenimore, E.E.: 1987, Applied Optics, 26,2760
Time-Resolved and Energy-Resolved Coded Aperture Images With Ura Tagging
Fenimore, E.E.,Blake, R.L.: 1980, Rev. Sci. Instrum., 51,445
Random Array Grid Collimators
X-ray collimators using grid patterns which are random offer several significant
advantages over collimators using periodic grids. In particular, random array
grid collimators (RAGC's) eliminate the requirement that there be very closely
spaced grids if a wide field of obscuration outside the central peak is desired.
The RAGC should be less susceptibel to systematic off-axis leaks, and the RAGC
has a better high energy response than a periodic grid collimator. The random
array technique can also be used to produce converging or diverging collimators.
A general theory is presented which predicts the angular response of a RAGC. It
is shown that pure random arrays have two problems: there are strong wings in
the response function and the patterns are not self-supporting. Restrictions on
the randomness of the pattern are suggested which eliminate these problems but
at the price of putting an upper limit on the available throughput. However,
even in the worst case, the upper limit for a two-dimensional collimator is as
high as 23%. In other cases, throughputs the order of 40% are possible with two-
dimensional collimators and of 50% with one-dimensional collimators with a large
collecting area. Suggestions are presented for easing the fabrication effort of
the grids.
Fenimore, E.E.,Cannon, T.M.: 1978, Applied Optics, 17,337
Coded Aperture Imaging With Uniformly Redundant Arrays
URA's have autocorrelation functions with perfectly flat sidelobes. The URA
combines the high transmission characteristics of the random array with the flat
sidelobe advantage of the non-redundant pinhole arrays. This gives the URA the
capability to image low-intensity, low-contrast sources. Furthermore, whereas
the inherent noise in random array imaging puts a limit on the obtainable SNR,
the URA has no such limit. Computer simulations show that the URA with
significant shot and background noise is vastly superior to random array
techniques without noise. Implementation permits a detector which is smaller
than its random array counterpart.
Fenimore, E.E.,Cannon, T.M.: 1981, Applied Optics, 20,1858
Uniformly Redundant Arrays - Digital Reconstruction Methods
Several new digital reconstruction techniques for coded aperture imaging are
developed which are especially applicable to URAs. The techniques provide
improved resolution without upsetting the artifact-free nature of URAs. Two new
techniques are described; one which allows self-supporting arrays and one which
avoids (or at least mitigates) a blur which has been associated with previous
correlation analyses. Each of the methods and their resolution improvements are
demonstrated with reconstruction of a laser-driven compression. Particular
emphasis has been placed on the special sampling required of the encoded picture
and the decoding function if artifacts are to be avoided. For large URAs, it is
known that another new digital technique, periodic decoding, is much faster.
Periodic decoding does produce artifacts, but they usually are negligible.
Fenimore, E.E.,Cannon, T.M.,Miller, E.L.: 1978, SPIE Proceedings, 149,232
Comparison of Fresnel Zone Plates and Uniformly Redundancy Arrays
Several imaging systems in laser fusion, e-beam fusion, and astronomy employ a
Fresnel zone plate (FZP) as a coded aperture. The recent development of URAs
promises several improvements in these systems. The first advantage of URA is
the fact that its modulation transfer function (MTF) is the same as the MTF of a
single pinhole, whereas the MTF of an FZP is an erratic function including some
small values. This means that if inverse filtering is used, the URA will be less
susceptible to noise. If a correlation analysis is used, the FZP will produce
artifacts whereas the URA has no artifact (assuming planar sources). Both the
FZP and URA originated from functions which had flat MTFs. However, practical
considerations in the implementation of the FZP detracted from its good
characteristics whereas the URA was only mildly affected. The second advantage
of the URA is that it better utilizes the available detector area. With the FZP,
the aperture should be smaller than the detector in order to obtain the full
angular resolution corresponding to the thinnest zone. The cyclic nature of the
URA allows one to mosaic it in such a way that the entire detector area collect
photons from all of the sources within the field of view while maintaining the
full angular resolution. If the FZP is as large (or larger) than the detector,
all parts of the source will not be resolved with the same resolution. The FZP
does have some advantages, in particular its radial symmetry eases the alignment
problem; it has a convenient optical decoding method; and higher diffraction
order reconstruction might provide better spatial resolution.
Fenimore, E.E.,Cannon, T.M.,Van Hulsteyn, D.B.,Lee, P.: 1979, Applied Optics,
18,945
Uniformly Redundant Arrays Imaging of LAser Driven Compressions: Preliminary
Results
Fenimore, E.E.,Weston, G.S.: 1981, Applied Optics, 20,3058
Fast Delta-Hadamard Transform
In many fields (e.g. spectroscopy, imaging spectroscopy, photo-acoustic imaging,
coded aperture imaging) binary bit patters known as m sequences are used to
encode (by multiplexing) a series of measurements in order to obtain a larger
throughput. The observed measurements must be decoded to obtain the desired
spectrum (or images in case of coded aperture imaging). Decoding in the past has
used a technique called the fast Hadamard transform (FHT) whose chief advantage
is that it can reduce the computational effort from N;2 multiplies to NlogN
additions or subtractions. However, the FHT has the disadvantage that it does
not readily allow one to sample more finely than the number of bits used in the
m sequence. This can limit the obtainable resolution and cause confusion near
the sample boundaries (phasing errors). We have developed both 1-D and 2-D
methods (called fast delta Hadamard transforms, FDHT) which overcome both the
above limitations. Applications of the FDHT are discussed in the context of
Hadamard spectroscopy and coded aperture imaging with URAs. Special emphasis has
been placed on how the FDHT can unite techniques used by both of these fields
into the same mathematical basis.
Fiddy, M.A.,Brames, B.J.,Dainty, J.C.: 1983, Optics Letters, 8,96
Enforcing Irreducibility for Phase Retrieval in 2 Dimensions
Fienup, J.R.,Idell, P.S.: 1988, Optical Engineering, 27,778
Imaging Correlography With Sparse Arrays of Detectors
Fleming, J.S.,Goddard, B.A.: 1982, Medical & Biological Engineering & Computing,
20,7
Comparison of Techniques for Stationary Coded Aperture Imaging in Nuclear-
Medicine
Fleming, J.S.,Goddard, B.A.: 1984, Nuclear Instruments & Methods in Physics
Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 221,242
An Evaluation of Techniques for Stationary Coded Aperture 3-Dimensional Imaging
in Nuclear-Medicine
Flynn, M.J.,Neumann, D.R.,Wake, R.H.,Wiener, S.N.: 1982, Journal of Nuclear
Medicine, 23,P59
A Hybrid Coded-Aperture Parallel-Plate Collimator for Multiview Cardiac Imaging
Galper, A.M.,Lazarev, S.A.,Luchkov, B.I.,Zerov, I.V.,Prilutskii, O.F.: 1981,
Kosmicheskie Issledovaniia, 19,947
Calculation of the Characteristics of a Gamma-Ray Telescope With a Coded
Aperture
A theoretical analysis shows that the aperture coding technique makes it
possible to substantially improve the angular resolution of a gamma-ray
telescope. Even in a system where the coding mask is relatively close to the
detector, the improvement in angular resolution is at least six-fold. However,
this improvement is accompanied by the loss of the telescope's ability to
isolate faint discrete sources above the isotropic background. (In Russian).
Garcia, M.R.,Grindlay, J.E.,Burg, R.,Murray, S.S.,Flanagan, J.: 1986, IEEE
Transactions On Nuclear Science, 33,735
Development of the EXITE Detector - A New Imaging Detector for 20 - 300 KeV
Astronomy
Gehrels, N.,Cline, T.L.,Huters, A.F.,Leventhal, M.,MacCallum, C.J.,Reber, J.D.,
Stang, P.D.,Teegarden, B.J.,Tueller, J.: 1985, Proc Nth Cosmic Ray Conference;
OG9.2, OG9.2,303
A Coded Aperture Imaging System for Hard X-Ray and Gamma-Ray Astronomy
Giles, A.B.: 1981, Applied Optics, 20,3068
Self-Supporting Perfect Masks for 2-D Infrared and X-Ray-Imaging
Gilfanov, M.,Churazov, E.,Sunyaev, R.,Grebenev, S.,Pavlinsky, M.,Dyachkov, A.,
Kovtunenko, V.,Kremnev, R.,Goldwurm, A.,Ballet, J.,Laurent, P.,Paul, J.,
Jourdain, E.,Schimtzfraysse, M.C.,Roques, J.P.,Mandrou, P.: 1993, Advances in
Space Research, 13,695
Hard X-Ray Spectral Properties and Discovery of Narrow Annihilation Line in the
Spectrum of Nova-Muscae
The observations of X-ray Nova in Musca (GRS1124-684) by two coded mask
telescopes on board GRANAT observatory provided spectral data in broad 3 - 1300
keV band. During these observations, spanned over a similar to year, the Nova
was detected in a three apparently different spectral states, corresponding to
different epochs of the soft X-ray light curve: (1) A spectrum with two distinct
components (soft, below similar to 8 keV and hard power law tail with slope
similar to 2.5, detected up to similar to 300 keV). The soft emission changed
gradually with characteristic decay time around 30 days, while power law
component exhibited strong variability on the time scales of several hours and
decreased much more slowly. (2) A soft spectrum (without hard power law tail),
observed during the ''kick'' of the soft X-ray light curve. (3) A hard power law
spectrum with slope similar to 2.2. Thus, while the 3 - 300 keV luminosity
decreased by more than order of magnitude, the source passed through all
spectral states known for galactic black hole candidates (Cyg X-1, GX339-4,
1E1740.7-2942, GRS1758-258 etc.). On January 20-21 1991, the SIGMA telescope
aboard GRANAT detected a relatively narrow variable emission line near 500 keV
(Fig.l,2) with net flux x 6 10(-3)phot/s/cm(2), most probably related with
electron-positron annihilation processes, occurring in the source /1-4/.
Additional excess above power law continuum, centered around similar to 200 keV,
was found during this observation.
Gilfanov, M.,Syunyaev, R.,Churazov, E.,Loznikov, V.,Efremov, V.,Kaniovskii, A.,
Kuznetsov, A.,Yamburenko, N.,Melioranskii, A.,Skinner, G.K.,Alemam, O.,
Patterson, T.G.,Willmore, A.P.,Brinkman, A.C.,Heise, J.,In 't Zand, J.J.M.,Jager,
R.,Voges, W.,Pietsch, W.,Doebereiner, S.,Englhauser, J.,Truemper, J.,Reppin, C.,
Oegelman, H.,Kendziorra, E.,Mony, B.,Maisack, M.,Staubert, R.,Parmar, A.N.,
Smith, A.: 1989, Soviet Astronomy Letters, 15,291
Observations of X-Ray Pulsars With the Roentgen Observatory On the Kvant Module
Gindi, G.R.,Arendt, J.,Barrett, H.H.,Chiu, M.Y.,Ervin, A.,Giles, C.L.,Kujoory,
M.A.,Miller, E.L.,Simpson, R.G.: 1982, Medical Physics, 9,324
Imaging With Rotating Slit Apertures and Rotating Collimators
Gindi, G.R.,Barrett, H.H.,Paxman, R.G.: 1982, Journal of the Optical Society of
America, 72,1737
Can a 3-Dimensional Object Be Derived from a 2-Dimensional Coded Image
Gindi, G.R.,Paxman, R.G.,Barrett, H.H.: 1984, Applied Optics, 23,851
Reconstruction of an Object from Its Coded Image and Object Constraints
Golay, M.J.E.: 1971, Journal of the Optical Society of America, 61,272
Point Arrays Having Compact, Non-Redundant Autocorrelations
Goldwurm, A.,Byard, K.,Dean, A.J.,Hall, C.J.,Harding, J.S.J.: 1990, Astronomy
and Astrophysics, 227,640
Laboratory Images With HURA Coded Apertures
In this paper we consider the possibility of using hexagonally uniformly
redundant array (HURA) coded apertures for high energy gamma ray telescopes
where discrete pixel detectors with low positional resolution are generally
used. Results of laboratory tests carried out to study the performance of a
coded aperture system using both a stationary and rotating HURA mask with a
discrete pixel detector are presented and compared to computer simulations. The
tests confirm the simulation results indicating that such a system, when the
standard cross-correlation deconvolution is applied, suffers from an intrinsic
systematic noise due to the asymmetrical mismatch between the mask elements and
the detector pixels. To reduce this coding error which is inherent to the system
two techniques have been developed and tested. For a stationary mask, a special
configuration using hexagonal pixel detector has been identified for which mask
elements are binned nearly exactly by the pixels and no coding error is present.
An efficient and fast algorithm, based on mean count subtraction and weighted
deconvolution, has also been developed in order to reduce the coding error when
a proper design of the system is infeasible or when a rotating mask is used.
Both of the above techniques have been proved to be effective, the second being
more suitable for rotating masks for which the coding error is smoothed in the
convolution stage by the mask rotation.
Gorenstein, P.,Helmken, H.,Gursky, H.: 1976, Astrophysics and Space Science, 42,
89
Localization of Gamma-Ray Bursts With Wide Field Multiple Pinhole Camera System
in Near Earth Orbit
A multiple pinhole camera system has been designed and proposed for a small
satellite of the SAS type for the detection and localization of gamma-ray
bursts. The instrument consists of a three unit array of detectors each of which
includes a semi-cylindrical collimator surrounding a two-dimensional position-
sensitive detector. The collimator contains slits of 1 mm width that are cut
parallel to the axis of the cylinder. The slits are randomly arranged in azimuth
around the cylinder. X-rays may enter the counter through several surfaces. The
point at which photoelectric interaction takes place is determined in two
dimensions in a plane perpendicular to the cylinder axis. Each unit of the
system determines the position of a burst to a great circle. An intersection of
two (or three) great circles provides the precise positions. The field of view
of the instrument is 2.7pi ster, essentially the entire region of the sky not
occulted by the Earth. It is designed to operate in 20-100 keV. An instrument
sized to fit a SAS spacecraft has a sensitivity of better than 10;-erg cm;-2 for
bursts whose intense phase occur in less than a total of three seconds. For
stronger bursts (larger than 10;-5 erg cm;-2) the location precision is better
than a minute of arc.
Gottesman, S.R.,Fenimore, E.E.: 1989, Applied Optics, 28,4344
New Family of Binary Arrays for Coded Aperture Imaging
We introduce a new family of binary arrays for use in coded aperture imaging
which are predicted to have properties and sensitivity (SNR) equal to that of
the URA. The new arrays, called MURA (modified URA), have decoding coefficients
all of which are unimodular, resulting in a reconstructed image with noise terms
completely independent of image-source structure. Although the new arrays are
derived from quadratic residues, they do not belong to the cyclic difference set
or set of pseudo-noise sequences and consequently are constructable in
configurations forbidden for those designs, thus providing the user with a wider
selection of aperture patterns to match his particular needs. With the addition
of MURAs to the family of binary arrays, all prime numbers can now be used for
making optimal coded apertures, increasing the number of available square
patterns by more than a factor of 3.
Gottesman, S.R.,Schneid, E.J.: 1986, IEEE Transactions On Nuclear Science, 33,
745
PNP - A New Class of Coded Aperture Arrays
We report on a new class of coded aperture arrays which has all the desirable
imaging characteristics of the URA, yet is constructible in dimensions which are
forbidden to that design. In addition, the new arrays (called PNP arrays, for
pseudo-noise product) are of self-supporting geometry, simplifying fabrication
and making them ideal candidates for situations where active collimators are
employed, as for example in high-energy gamma-ray imaging. A unique and
important feature of all PNP arrays is the ability to produce reconstructed
images whose noise is uniform regardless of the original source structure. A
comparison of the predicted performance of the PNP, URA, GEOMETRIC, and PINHOLE
designs is presented.
Gourlay, A.R.,Stephen, J.B.: 1983, Applied Optics, 22,4042
Geometric Coded Aperture Masks
Gourlay, A.R.,Stephen, J.B.,Young, N.G.S.: 1984, Nuclear Instruments & Methods
in Physics Research Section A-Accelerators Spectrometers Detectors and
Associated Equipment, 221,54
Geometrically Designed Coded Aperture Mask Arrays
Gourlay, A.R.,Young, N.G.: 1984, Applied Optics, 23,4111
Coded Aperture Imaging - A Class of Flexible Mask Designs
A general class of coded aperture masks woth certain perfect decoding properties
are described. These masks are flexible in design in terms of both their shape
and openness ratio.
Grindlay, J.E.,Covault, C.E.,Manandhar, R.P.: 1993, Astronomy & Astrophysics
Supplement Series, 97,155
EXITE Observation of the Galactic-Center - A New Transient
The balloon-borne Energetic X-ray Imaging Telescope Experiment (EXITE) observed
the galactic center on May 9, 1989. Within the 3.4-degrees (FW H M) field of
view, imaged with 22' resolution at 20-250 keV, two sources were detected: the
'Einstein source' (1E1740.7-2942) and a possible second source approximately 40'
West (EXS1737.9-2952). This source was detected significantly at both 20-30 keV
and 83-111 keV, suggesting a double-backscattered 511 keV line source at 102 keV
and a soft excess, perhaps from a black hole candidate undergoing a transient
outburst.
Grindlay, J.E.,Garcia, M.R.,Burg, R.I.,Murray, S.S.: 1986, IEEE Transactions On
Nuclear Science, 33,750
The Energetic X-Ray-Imaging Telescope Experiment (EXITE)
Grindlay, J.E.,Murray, S.S.: UNKNOWN YEAR, Aip Conference Proceedings, 1982,477
Proposed Hard X-Ray-Imaging and Gamma-Ray Burst Studies for Xte
Groh, G.,Hayat, G.S.,Stroke, G.W.: 1972, Applied Optics, 11,931
X-Ray and Gamma-Ray Imaging With Multiple-Pinhole Cameras Using a Posteriori
Image Synthesis
Groh, G.,Stroke, G.W.: 1970, Optics Communications, 1,339
Information Retrieval from Coded Images Formed By Generalized Imaging Systems
Gunson, J.,Polychronopulos, B.: 1976, Monthly Notices of the Royal Astronomical
Society, 177,485
Optimum Design of a Coded Mask X-Ray Telescope for Rocket Applications
The paper considers an X-ray telescope based on a two-step imaging technique
that involves the formation of a shadowgram of the X-ray source by means of a
coded mask built up from opaque and transparent elements. With this technique,
the shadowgram is recorded on a suitable position-sensitive detector, and the
recording is processed by computer to reconstruct the desired image of the
source. These procedures are analyzed, technical problems are discussed, and it
is shown that periodic masks with convolution patterns completely free from
spurious peaks are optimum. Theoretical as well as practical design
considerations are examined for rocket applications of an X-ray telescope system
utilizing one- or two-dimensional optimum masks. An autocollimating mask is
described in detail, the effect of photon noise on image quality is evaluated,
and mask parameters are computed which give the best discrimination against
noise for a given set of viewing conditions. A computer simulation of a
shadowgraph and source image is provided as an example. It is concluded that
coded-shadowmask telescopes are useful in noisy situations only if the field of
view under observation is sparsely populated with point sources or extended
sources of small angular spread.
Gurker, N.: 1985, X-Ray Spectrometry, 14,74
X-Ray Mapping Using a New Coded Irradiation Technique
Gurov, A.Y.,Fedotov, S.N.: 1990, Instruments and Experimental Techniques, 33,
1060
Comparison of Gamma-Telescope Sensitivities in the Energy-Range of 1-5 MeV
The sensitivities of a Compton gamma telescope (CGT) and a coded-aperture
telescope (CAT) in the range of gamma-quantum energies of 1-5 MeV are compared.
The effects of the energy resolution of the detectors for the CGT and of the
finite transparency of the coded mask for the CAT are taken into account in the
calculations. Sensitivity calculations are performed for various measurement
times and background levels. The sensitive area of the instruments is assumed to
be 10(4) cm2. The sensitivities of the telescopes are compared with the
sensitivity of a collimated total-absorption spectrometric detector.
Haaker, P.,Klotz, E.,Koppe, R.,Linde, R.,Moller, H.: 1985, Medical Physics, 12,
431
A New Digital Tomosynthesis Method With Less Artifacts for Angiography
Haberl, F.: 1984, - Thesis, MPI-Garching
Untersuchungen an Einer Kodierten Lochkamera Fuer Astronomische Messungen Im
Harten Roentgenbereich
Hammersley, A.P.: 1986, Ph.D. Thesis, University of Birmingham
The Reconstruction of Coded Mask Data Under Conditions Realistic to X-Ray
Astronomy Observations
Hammersley, A.P.: 1991, Computer Journal, 34,362
Efficient 2-Dimensional Fast Fourier-Transform Subroutines for Real-Valued or
Hermitian Data
Hammersley, A.,Ponman, T.,Skinner, G.: 1992, Nuclear Instruments & Methods in
Physics Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 311,585
Reconstruction of Images from a Coded-Aperture Box Camera
Methods for the reconstruction of images from coded-aperture box cameras are
discussed. A fast reconstruction method for unbiased reconstruction is presented
and examples of its application to simulated and real data are given. An
interative procedure to further reduce coding noise is proposed and its
effectiveness quantified.
Hammersley, A.P.,Skinner, G.K.: 1984, Nuclear Instruments & Methods in Physics
Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 221,45
Data-Processing of Imperfectly Coded Images
The theory of mask coding is well established for perfect coding systems, but
imperfections in practical situations produce new data processing problems. The
Spacelab 2 telescopes are fully coded systems, but some complications arise as
parts of the detector are obscured by a strengthening cross. The effects of this
sort of obscuration on image quality and ways of handling them will be
discussed.
Hanson, C.G.,Skinner, G.K.,Eyles, C.J.,Willmore, A.P.: 1989, Monthly Notices of
the Royal Astronomical Society, 240,P1
Coded Mask X-Ray Images of the Large Magellanic Cloud - Hard X-Ray-Emission from
EXO 053109-6609.2
Hanson, C.G.,Skinner, G.K.,Eyles, C.J.,Willmore, A.P.: 1990, Monthly Notices of
the Royal Astronomical Society, 242,262
Coded Mask X-Ray Images of the Virgo Cluster .1. Hard X-Rays from the Seyfert-
Galaxy Ngc-4388
Harper, P.K.S.,Skinner, G.K.,Eyles, C.J.,Wilmore, A.P.,Bertram, D.,Herring,
J.R.H.,Peden, J.C.M.,Pollock, A.M.T.,Ponman, T.J.: 1987, Journal of the British
Interplanetary Society, 40,163
Flight of the Spacelab X-Ray Telescope
The hard X-ray imaging telescope built at the University of Birmingham and
described elsewhere in this issue flew on the Spacelab 2 mission in July/August
1985. The instrument was primarily designed to study the diffuse X-ray emission
from clusters of galaxies. During the mission, observations were successfully
made of six clusters, a supernova remnant, and the region around the Galactic
Centre. This paper describes the preparations for the telescope's flight, and
the mission operations. (Author abstract) 3 refs.
Harvey, J.E.,Kotha, A.: 1994, Optics Communications, 106,178
Sparse Array Configurations Yielding Uniform Mtfs in Reciprocal Path Imaging
Applications
A method is presented for constructing both one-dimensional and two-dimensional
configurations of sparse subaperture arrays which result in uniform spatial
frequency response with arbitrarily high spatial resolution for reciprocal path
imaging applications (i.e., imaging laser radar applications).
Harvey, J.E.,Rockwell, R.A.: 1988, Optical Engineering, 27,762
Performance-Characteristics of Phased-Array and Thinned Aperture Optical
Telescopes
Harwit, M.,Sloane, N.J.A. (1979): Hadamard Transform Optics. 1st ed. Academic
Press, New York.
Heindl, W.A.,Cook, W.R.,Grunsfeld, J.M.,Palmer, D.M.,Prince, T.A.,Schindler,
S.M.,Stone, E.C.: 1993, Astrophysical Journal, 408,507
An Observation of the Galactic-Center Hard X-Ray Source, 1E 1740.7-2942 With the
Caltech Coded-Aperture Telescope
The Galactic center region hard X-ray source 1E 1740.7-2942 has been observed
with the Caltech Gamma-Ray Imaging Payload (GRIP) from Alice Springs, Australia,
on 1988 April 12 and on 1989 April 3 and 4. We report here results from the 1989
measurements based on 14 hr of observation of the Galactic center region. The
observations showed 1E 1740.7-2942 to be in its normal state, having a spectrum
between 35 and 200 keV characterized by a power law with an exponent of -2.2 +/-
0.3 and flux at 100 keV of (7.0 +/- 0.7) x 10(-5) cm-2 s-1 keV-1. No flux was
detected above 200 keV. A search for time variability in the spectrum of 1E
1740.7-2942 on one hour time scales showed no evidence for variability.
Herring, J.R.H.,Skinner, G.K.,Emam, O.: 1991, Nuclear Instruments & Methods in
Physics Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 310,341
A Cylindrical Surface MWPC for All-Round X-Ray Vision
We describe the design, construction and performance of a novel type of position
sensitive multiwire proportional counter intended for use in a proposed coded
mask all-sky X-ray monitor. The sensitive volume is in the form of a cylindrical
shell inside a tubular carbon fibre window. The electronic system uses
multichannel preamplifier chips developed at CERN, and includes logic and
digitising circuits for direct readout to a computer.
Hogge, C.B.,Schultz, J.F.,Mason, D.B.,Thompson, W.E.: 1988, Applied Optics, 27,
5127
Physical Optics of Multiaperture Systems
Hudson, H.S.: 1982, Advances in Space Research, 2,307
The Pinhole/Occulter Facility
The Pinhole/Occulter Facility concept uses a remote occulting mask to provide
high resolution observations of the solar corona and of astronomical X-ray
sources. With coded-aperture and Fourier-transform techniques, the Pinhole/
Occulter makes images at a resolution of 0.2 arc sec for 2-120 keV X-rays, using
a 50-m boom erected from the payload bay of the Space Shuttle or mounted on a
free-flying platform. The remote occulter also creates a large shadow area for
solar coronal observations; the Pinhole/Occulter concept includes separate
optical and ultraviolet telescopes with 50-cm apertures. These large telescopes
will provide a new order of resolution and sensitivity for diagnostic
observations of faint structures in the solar corona. The Pinhole/Occulter is a
powerful and versatile tool for general-purpose X-ray astronomy, with excellent
performance in a broad spectral band complementary to that accessible with AXAF.
The large collecting area of 1.5 sq m results in a 5 sigma detection threshold
of about 0.02 microJy for the 2-10 keV band.
Indebetouw, G.: 1986, Optics and Laser Technology, 18,268
Scanning Heterodyne Reconstruction of Coded Aperture Images
Indebetouw, G.,Shing, W.P.: 1981, Journal of the Optical Society of America, 71,
1627
Optical Reconstruction of Coded Aperture Images
Indebetouw, G.,Shing, W.P.: 1981, Applied Optics, 20,3996
Optical-Scanning Reconstruction of Fresnel Zone Plate Coded Images
Indebetouw, G.,Shing, W.P.: 1982, Applied Physics B-Photophysics and Laser
Chemistry, 27,69
Scanning Optical Reconstruction of Coded Aperture Images
In 't Zand, J.J.M.: 1992, Ph.D. Thesis, University of Utrecht
A Coded-Mask Imager As Monitor of Galactic X-Ray Sources
In 't Zand, J.J.M.,Heise, J.,Jager, R.: 1994, Astronomy and Astrophysics, 288,
665
The Optimum Open Fraction of Coded Apertures With an Application to the Wide
Field X-Ray Cameras of SAX
We consider issues that concern the mathematical description of coded aperture
patterns. Primarily this involves the relation between the open fraction of such
patterns and the signal-to-noise ratio of imaged point sources. A refinement of
the corresponding theory is introduced, taking into account the spatial response
of the coded aperture camera. From this we predict that patterns with an open
fraction of less than 0.5 can enhance the performance of coded aperture cameras
to bright sources, as opposed to what was previously thought. As an application
of the refined theory, we tested candidate open fractions in the instrumental
configuration of two identical, wide field, coded aperture X-ray cameras (1.8-30
keV), that will be part of the X-ray satellite SAX (to be launched in late
1995). These tests consisted of numerical simulations of several types of
observations, and show that open fractions between 0.25 and 0.33 are to be
favored for the SAX cameras. The improvement in signal-to-noise ratio with
respect to the commonly used open fraction of 0.5 is up to 30%. WHenever
telemetry limits the data coverage, this profit may well be larger. We also
address additional aperture constraints as applied to the SAX cameras, such as
the aperture geometry and pattern. From this analysis we propose a new type of
coded aperture pattern for the SAX cameras with an open fraction equal to 0.33,
which possesses near-ideal mathematical properties.
In 't Zand, J.J.M.,Pan, H.C.,Bleeker, J.A.M.,Skinner, G.K.,Gilfanov, M.R.,
Sunyaev, R.A.: 1992, Astronomy and Astrophysics, 266,283
The Spectral Variability in 2-28 Kev of GS2023+338 During Its 1989 Outburst
The X-ray transient GS2023+338 (=V404 Cyg in the optical band), a close binary
containing a black hole candidate, was observed with the coded mask X-ray camera
TTM of the Rontgen observatory on the Kvant module of Mir during June-August
1989, when it was in outburst. We report here the results of an analysis of
these observations, which mainly addresses the SPECTRAL variability of the
transient on time scales between minutes and months. The spectral signatures of
this variability were found to consist of a fluctuating low-energy absorption
with a time scale of approximately 1 1/2 h, whose amplitude decreased on a time
scale of approximately 1 month, and a slowly decreasing Compton-reflected
component, on top of a power-law spectrum with essentially a constant photon
index of 1.6-1.7. The fluctuating low-energy absorption could be satisfactory
modeled by a varying column density of cold matter, with a dynamical range of at
least a factor of - 40 and ranging up to N(H) almost-equal-to 4.5 x 10(23) H cm-
2. This variability most probably originated in dynamical processes. Apart from
spectral variability, a wavelength-independent variability is apparent, which
had time scales down to at least minutes, on top of a general decay with an e-
folding decay time of 32 days. The long-term trends suggest that the environment
of the compact object became progressively more transparent by accretion of the
circumstellar matter onto the compact object. The total mass transferred to the
compact object during the complete outburst was, through equivalence with the
radiated energy during the total outburst, found to be approximately 2 x 10(-9)
(D/1 kpC)2 M. This is equivalent to an average mass transfer rate from the
companion during the quiescent stage since the last outburst of the optical
counterpart of (4-12) x 10(15) (D/1 kpc)2 g s-1, which is similar to that
observed in other transient low-mass X-ray binaries, as long as D < 3 kpc. In
many of its spectral aspects, GS2023+338 resembles the galactic black hole
candidate Cyg X-1 in its 'hard' state.
Islam, M.K.,Fitzgerald, L.T.,Bova, F.J.,Mauderli, W.: 1993, Physics in Medicine
and Biology, 38,1403
A Coded-Aperture Device for Online Imaging With Megavoltage Photon Beams
A prototype coded aperture device based upon a liquid-filled strip ion chamber
has been investigated as an on-line imaging unit for portal imaging of
megavoltage photon beams. The strip ion chamber was used to collect integrated
data for a series of pixels along a line across the field of view. By
translating the detector, in equal steps in a direction perpendicular to its
length, the data for a complete projection of the image were collected.
Multiple-projection data, corresponding to different angular views, were
collected by sequentially rotating the detector in equal angular steps and then
translating through the field. The portal image was reconstructed from the
multiple-projection data by a convolution-filtered back-projection algorithm.
The phantom images taken with a cobalt-60 radiation source were found to be of
similar contrast to film images. The signal-to-noise ratio, including the noise
propagation of the reconstruction process for an image of 101 x 101 pixels, was
207:1. For a translational step of 2 mm the spatial resolution of the system was
found to be 4.2 mm, as determined from the full width at half maximum of the
point spread function.
Jacroux, M.,Notz, W.: 1983, Annals of Statistics, 11,970
On the Optimality of Spring Balance Weighing Designs
Jager, R.,Heise, J.,In 't Zand, J.J.M.,Brinkman, A.C.: 1993, Advances in Space
Research, 13,315
Wide-Field Cameras for Sax
SAX is an Italian X-ray satellite with a Dutch contribution that will be placed
in orbit in 1994. The prime scientific object of SAX is to cover an energy
bandwidth that ranges from 0.1 keV upto 200 keV. Among other instruments, SAX
will consist of two X-ray Wide Field Cameras built by the Space Research
Organisation Netherlands at Utrecht. The WFCs are based on the coded mask
principle, the reconstruction of the image takes place on ground. The field of
view is 20 degrees square full width at half maximum (FWHM), the angular
resolution 5 arcminutes (FWHM) and the energy band ranges from 1.8 to 30 keV
with a resolution of 18% at 6 keV. The sensitive area is 200 cm(2) at 6 keV. The
mask pattern is based on a pseudo random array with 255 x 257 elements of 1
mm(2), 50% of which are transparent.
Jayanthi, U.B.,Braga, J.: 1991, Nuclear Instruments & Methods in Physics
Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 310,685
Physical Implementation of an Antimask in Ura Based Coded Mask Systems
X- and gamma-ray astronomy experiments which employ rectangular URA coded masks
alone show artifacts in the images reconstructed due to nonuniform background
levels in the detector plane. The employment of a separate antimask in addition
to the mask in observations is useful to eliminate this problem. We propose here
a method to implement the antimask with the same mask, utilizing the
antisymmetric properties in the mask pattern, thereby avoiding the need for a
separate antimask in an experiment. Simulations performed with this mask-
antimask system are presented to show its advantages.
Jedwab, J.,Mitchell, C.: 1988, Electronics Letters, 24,650
Constructing New Perfect Binary Arrays
Jedwab, J.,Mitchell, C.J.: 1990, Electronics Letters, 26,294
Infinite Families of Quasiperfect and Doubly Quasiperfect Binary Arrays
Jedwab, J.,Mitchell, C.,Piper, F.,Wild, P.: 1994, Discrete Mathematics, 125,241
Perfect Binary Arrays and Difference Sets
A perfect binary array is an r-dimensional array with elements +/- 1 such that
all out-of-phase periodic autocorrelation coefficients are zero. Such an array
is equivalent to a Menon difference set in an abelian group. We give recursive
constructions for four infinite families of two-dimensional perfect binary
arrays, using only elementary methods. Brief outlines of the proofs were
previously given by three of the authors. Although perfect binary arrays of the
same sizes as two of the families were constructed earlier by Davis, the sizes
of the other two families are new.
Jenkins, T.L.,Frye, G.M.,Owens, A.,Carter, J.N.,Ramsden, D. (1981): Accelerator
test of the coded aperture mask technique for gamma-ray astronomy. In:
Proceedings of the 17th International Cosmic Ray Conference - Paris. Vol. 9. (:
) Commissariat a l'Energie Atomique, Gif-sur-Yvette, France, 283-286.
(Case Western Reserve University, Cleveland; Southampton, University,
Southampton, England)
Jenkins, T.L.,Frye, G.M.,Owens, A.,Carter, J.N.,Ramsden, D.: 1984, Nuclear
Instruments & Methods in Physics Research Section A-Accelerators Spectrometers
Detectors and Associated Equipment, 221,278
A Gamma-Ray Telescope With Arc Minute Resolution
Jimenez, J.,Olmos, P.,Depablos, J.L.,Perez, J.M.: 1991, Applied Optics, 30,549
Gamma-Ray Imaging Using Coded Aperture Masks - A Computer-Simulation Approach
The gamma-ray imaging using coded aperture masks as focusing elements is an
extended technique for static position sensitive detectors. Several transfer
functions have been proposed to implement mathematically the set of holes in the
mask, the uniformly redundant array collimator being the most popular design. A
considerable amount of work has been done to improve the digital methods of
deconvolve the gamma-ray image, formed at the detector plane, with this transfer
function. Here we present a study of the behavior of these techniques when
applied to the geometric shadows produced by a set of point emitters. Comparison
of the shape of the object reconstructed from these shadows with that resulting
from the analytical reconstruction is performed, defining the validity ranges of
the usual algorithmic approximations reported in the literature. Finally,
several improvements are discussed.
Johansson, A.,Beron, B.L.,Campbell, L.,Eichler, R.,Hofstadter, R.,Hughes, E.B.,
Wilson, S.,Gorodetsky, P.: 1980, IEEE Transactions On Nuclear Science, NS-27,
375
The Use of an Active Coded Aperture for Improved Directional Measurements in
High Energy Gamma-Ray Astronomy
The coded aperture, a refinement of the scatter-hole camera, offers a method for
the improved measurement of gamma-ray direction in gamma-ray astronomy. Two
prototype coded apertures have been built and tested. The more recent of these
has 128 active elements of the heavy scintillator BGO. Results of tests for
gamma-rays in the range 50-500 MeV are reported and future application in space
discussed.
Johnson, T.W.,Park, J.B.,Dyer, S.A.,Harms, B.K.,Dyer, R.A.: 1989, Applied
Spectroscopy, 43,746
An Efficient Method for Recovering the Optimal Unbiased Linear Spectrum-Estimate
from Hadamard-Transform Spectrometers Having Nonideal Masks
Jorgenson, M.B.,Fattouche, M.,Nichols, S.T.: 1991, IEE Proceedings - H
Microwaves Antennas and Propagation, 138,441
Applications of Minimum Redundancy Arrays in Adaptive Beamforming
It is shown, through analysis and simulation, that the use of a minimum
redundancy array (MRA) in conjunction with an adaptive beamformer results in
performance superior to that attained by a comparable system based on an array
with uniformly spaced elements, or uniform array (UA) in terms of rejecting
interferences located in close angular proximity to the look direction. Further,
it is demonstrated that choosing the adaptive elements of a thinned adaptive
array (TAA) based on a minimum spatial redundancy criterion, rather than spacing
them uniformly, results in improved rejection of main lobe interferences, with
negligible degradation in sidelobe interference rejection capabilities.
Jourdain, E.,Bassani, L.,Roques, J.P.,Mandrou, P.,Ballet, J.,Laurent, P.,Lebrun,
F.,Paul, J.,Finogenov, A.,Churazov, E.,Gilfanov, M.,Sunyaev, R.,Dyatchkov, I.,
Khavenson, N.,Novikov, B.,Kuleshova, N.: 1993, Advances in Space Research, 13,
705
The Observations of AGNs in the 40-1300 KeV Energy-Range By the Sigma-Telescope
SIGMA telescope realizes images of the sky in the hard X-ray domain (40 keV-1.3
MeV) through a coded mask system. The extragalactic study was one of the main
objectives and has brought new results in our knowledge of the Active Galactic
Nuclei behavior at high energy. In fact, the variability in the most important
factor as all these objects have been showed to display strong evolution in
intensity or/and spectral shape. Moreover, the discovery of a new hard X-ray
source close to 3C273 and probably strongly absorbed below 40-50 keV could have
many consequences in the extragalactic field.
Jupp, I.D.,Byard, K.,Dean, A.J.: 1994, Nuclear Instruments & Methods in Physics
Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 345,576
An Improved Sampling Configuration for a Coded-Aperture Telescope
The sensitivity of a gamma-ray coded aperture telescope has been studied in
order to investigate the trade-off between angular resolution and the
reconstructed image signal to noise ratio (SNR) that occurs when a discrete
pixel detector is used. Without fine sampling of the coded mask by the detector
plane, the reconstructed SNR is seriously compromised if the source under
observation lies close to sky pixel boundaries, falling to as low as 25% of the
maximum SNR. Fine sampling partially restores the image SNR, but at the expense
of the telescope angular resolution. However, it is shown that the use of a non-
integer fine sampling value, for example 1.5 X 1.5 detector pixels per mask
element, can be used to achieve high image SNR whilst retaining good angular
resolution.
Kelly, J.G.,Stalker, K.T.: 1981, Transactions of the American Nuclear Society,
38,379
Status of the Coded Aperture Imaging Fuel Motion System (Cais)
Kendziorra, E.,Kretschmar, P.,Pan, H.C.,Kunz, M.,Maisack, M.,Staubert, R.,
Pietsch, W.,Trumper, J.,Efremov, V.,Sunyaev, R.: 1994, Astronomy and
Astrophysics, 291,L31
Evidence for Cyclotron Line Features in High-Energy Spectra of A0535+26 During
the March/April-1989 Outburst
The X-ray pulsar A 0535+26 has been observed during its March/April 1989
outburst with the Coded Mask Telescope TTM and the High Energy X-ray Experiment
HEXE on board the Mir space station at energies between 4 and 156 keV. Pulsed
emission (P=103.26 s for JD 244 7626) has been detected up to at least 100 keV.
Above 20 keV the time averaged pulse profiles show a clear double peak structure
with an asymmetric main pulse and a more symmetric secondary pulse. The spectrum
of the main pulse is significantly harder than that of the secondary pulse. The
phase resolved spectra can only be fitted by a power law with exponential cutoff
modified by two absorption lines around 50 and 100 keV. We interpret these
features as the fundamental and first harmonic cyclotron resonances. The
corresponding strength of the magnetic field of the neutron star is 4.3 x 10(12)
Gauss.
Klemperer, W.K.: 1974, Astronomy & Astrophysics Supplement Series, 15,449
Very Large Array Configurations for the Observaions of Rapidly Varying Sources
Klotz, E.,Weiss, H.: 1974, Optics Communications, 11,368
Three Dimensional Codewd Aperture Imaging Using Nonredundant Point
Distributions
A nonredundant distribution of ten point sources is used for coded aperture
imaging. The coded image of a three dimensional X-ray object is decoded by means
of an incoherent projection system in all its layers. This decoding process
avoids all the adjustement problems of coherent processing systems.
Kohman, T.P.: 1989, Review of Scientific Instruments, 60,3396
Coded-Aperture X-Ray or Gamma-Ray Telescope With Least-Squares Image-
Reconstruction .1. Design Considerations
Kohman, T.P.: 1989, Review of Scientific Instruments, 60,3410
Coded-Aperture X-Ray or Gamma-Ray Telescope With Least-Squares Image-
Reconstruction .2. Computer-Simulation
Kopilovich, L.E.: 1984, Optica Acta, 31,1409
Non-Redundant Aperture Mask Systems for Interferometric Image Synthesis - A
Regular Method of Construction
Kopilovich, L.E.: 1988, Optics Communications, 68,7
Construction of Nonredundant Masks Over Square Grids Using Difference Sets
Kopilovich, L.E.: 1988, Electronics Letters, 24,566
On Perfect Binary Arrays
Kopilovich, L.E.: 1988, Radiotekhnika I Elektronika, 33,1918
Optimization of Two-Dimensional Aperture Synthesis Systems
Kopilovich, L.E.: 1989, Cybernetics, 25,153
Difference Sets in Noncyclic Abelian-Groups
Kopilovich, L.E.: 1992, IEE Proceedings-F Radar and Signal Processing, 139,365
New Approach to Constructing 2-Dimensional Aperture Synthesis Systems
The problem of constructing aperture synthesis (AS) systems which cover a given
rectangular domain of spatial frequencies with a minimum of receiving elements
is considered. A method for obtaining two-dimensional AS systems by multiplying
linear minimum redundancy AS systems is proposed. On the basis of difference
sets, AS systems for large domains are suggested. The redundancy of such systems
reaches 32-33%, whereas that of T systems for square domains is 50% and for
rectangular domains not less than The general estimates of the minimum-41%.
redundancy two-dimensional AS systems indicate that the construction suggested
in this work can be regarded as a step towards optimal AS systems.
Kopilovich, L.E.,Sodin, L.G.: 1989, Radiotekhnika I Elektronika, 34,2059
Linear Aperiodic Antenna-Arrays Based On Difference Sets
Kopilovich, L.E.,Sodin, L.G.: 1991, IEE Proceedings - H Microwaves Antennas and
Propagation, 138,233
2-Dimensional Aperiodic Antenna-Arrays With a Low Sidelobe Level
A method for the synthesis of two-dimensional aperiodic antenna arrays with a
low sidelobe level is suggested and studied. It extends Leeper's approach to the
synthesis of linear arrays based on cyclic difference sets. The method reported
here is based on a new combinatorial construction called generalised two-
dimensional difference sets. Ways of constructing such sets and the basic
features of the antennas obtained are considered.
Kopilovich, L.E.,Sodin, L.G.: 1993, Astronomy Letters, 19,457
Synthesis of Coded Masks for X-Ray and Gamma-Ray Telescopes
We suggest that coded masks for x-ray and gamma-ray telescopes be synthesized
using two-dimensional difference sets in square and rectangular apertures. In
comparison to the constructions now used, this considerably expands the
possibilities for choosing mask dimensions and the fraction of ''open''
sections, i.e., for improving the telescope resolution and sensitivity, without
any degradation of image quality. We also point out the possibility of
developing masks based on generalized two-dimensional difference sets,
additionally augmenting the set of feasible versions.
Kopilovich, L.E.,Sodin, L.G.: 1994, Radiotekhnika I Elektronika, 39,380
Synthesis of 2-Dimensional Nonequidistant Antenna-Arrays Using Difference Set-
Theory
Kopilovich, L.E.,Sodin, L.G.: 1994, Monthly Notices of the Royal Astronomical
Society, 266,357
Synthesis of Coded Masks for Gamma-Ray and X-Ray Telescopes
We propose the synthesis of coded masks for gamma-ray and X-ray telescopes with
square or rectangular apertures, using two-dimensional difference sets. Compared
with masks employed at present, these facilitate a significant increase in the
capability to choose both the size and the fraction of the 'open' pixels, i.e.
the telescope resolution and sensitivity. We also point out the possibility of
constructing masks on the basis of two-dimensional generalized difference sets,
which considerably increases the number of feasible variants.
Kujoory, M.A.,Miller, E.L.,Barrett, H.H.,Gindi, G.R.,Tamura, P.N.: 1980, Applied
Optics, 19,4186
Coded Aperture Imaging of Gamma-Ray Sources With an Off-Axis Rotating Slit
Laudet, P.,Roques, J.P.: 1988, Nuclear Instruments & Methods in Physics Research
Section A-Accelerators Spectrometers Detectors and Associated Equipment, 267,
212
Correction for Detector Uniformity of a Gamma-Ray Telescope Using Coded Aperture
Imaging
Laudet, P.,Roques, J.P.: 1988, Applied Optics, 27,4226
Resolution of Strong Sources for a Gamma-Ray Telescope Using Coded Aperture
Imaging
Laudet, P.,Roques, J.P.: 1989, Applied Optics, 28,755
Iterative Algorithm to Improve the Separating Power On Coded-Aperture Images
Lefkopoulos, D.,Danet, B.,Guilhem, J.B.,Morucci, J.P.,Guiraud, R.: 1983,
Proceedings of the Society of Photo-Optical Instrumentation Engineers, 312,188
Attainment of 3-D Images in Nuclear-Medicine By Coded-Aperture Devices
Lempel, A.: 1979, Applied Optics, 18,4064
Hadamard and M-Sequence Transforms Are Permutationally Similar
Linebarger, D.A.: 1992, IEEE Transactions On Antennas and Propagation, 40,1109
A Fast Method for Computing the Coarray of Sparse Linear Arrays
A fast algorithm for computing the coarray of sparse linear arrays is presented.
Deriving linear minimum redundancy arrays or linear minimum hole arrays involves
huge searches over candidate arrays to determine which arrays have the desired
coarray characteristics. Since the number of candidate arrays grows very large
with increasing numbers of sensors, it is important to be able to check each
array's coarray quickly so that the search does not take too long. The method
presented herein for computing coarrays is considerably faster than existing
methods. This algorithm is well suited to implementation on a digital computer-
it exploits the fact that integer multiplication is equivalent to convolution of
the integer's representations.
Linebarger, D.A.,Sudborough, I.H.,Tollis, I.G.: 1993, IEEE Transactions On
Information Theory, 39,716
Difference Bases and Sparse Sensor Arrays
Difference bases are discussed and their relevance to sensor arrays is
described. Several new analytical difference base structures that result in near
optimal low-redundancy sensor arrays are introduced. Algorithms are also
presented for efficiently obtaining sparse sensor arrays and/or difference
bases. Lastly, new bounds, related to arrays that have both redundancies and
holes in their coarray are presented. Also, some extensions to the idea of
difference bases that may yield useful results for sensor array design are
discussed.
Liu, L.: 1982, Applied Optics, 21,2817
Quasi-Interferometry With Coded Correlation Filtering
Luke, H.D.: 1988, IEEE Transactions On Aerospace and Electronic Systems, 24,287
Sequences and Arrays With Perfect Periodic Correlation
Luke, H.D.,Bomer, L.,Antweiler, M.: 1989, Signal Processing, 17,69
Perfect Binary Arrays
Lum, K.S.K.,Manandhar, R.P.,Eikenberry, S.S.,Krockenberger, M.,Grindlay, J.E.:
1994, IEEE Transactions On Nuclear Science, 41,1354
Initial Performance of the EXITE2 Imaging Phoswich Detector Telescope for Hard
X-Ray Astronomy
We have developed, tested, and flown a large-area imaging phoswich detector/
telescope for hard X-ray astronomy. This second-generation Energetic X-ray
Imaging Telescope Experiment (EXITE) is designed to detect and image cosmic X-
ray sources in the 20-600 keV energy range from a high-altitude balloon. Imaging
is accomplished via the coded-aperture technique. Laboratory tests have shown
that the detector achieves 14% (FWHM) energy resolution and approximately 10 mm
(FWHM) spatial resolution at 60 keV, and that the pulse-shape discrimination
(PSD) circuit effectively distinguishes between NaI(T1) and CsI(Na) events from
approximately 40-400 keV. The first flight of the instrument was from Palestine,
Texas, on 13-14 June 1993. In this paper, we present details of the laboratory
performance of the system and some flight results.
Maggioli, P.P.,Caroli, E.,Natalucci, L.,Spizzichino, A.: 1984, Nuclear
Instruments & Methods in Physics Research, 221,82
A Numerical Method for Recognition of Virtual Images in Coded Mask Telescopes
A Numerical Method for Recognition of Virtual Images in Coded Mask Telescopes" A
problem with telescopes utilizing replicated structure coded masks is the
possible occurrence of virtual images. A numerical method to discriminate
virtual from real images, and to determine their correct location in the field
of view, is described. The performance and reliability of this method, based on
eight "ad hoc" modifications of the coding array, have been investigated by
Monte Carlo simulations.
Maggioli, P.P.,Caroli, E.,Natalucci, L.,Spizzichino, A.,Badiali, M.: 1984,
Nuclear Instruments & Methods in Physics Research Section A-Accelerators
Spectrometers Detectors and Associated Equipment, 221,82
A Numerical-Method for Recognition of Virtual Images in Coded Mask Telescopes
Maisack, M.,Kendziorra, E.,Pan, H.C.,Skinner, G.K.,Pietsch, W.,Reppin, C.,
Efremov, V.,Sunyaev, R.: 1994, Astronomy and Astrophysics, 283,841
Thermal Comptonization in 4U1700-377
We present results of a broad band X-ray observation of the high-mass X-ray
binary 4U 1700-377 (HD 153919) with the Kvant observatory in the energy range 4-
100 keV. We find that a simple bremsstrahlung spectrum, which has been suggested
by previous hard X-ray observations, is not a good description of the 4-100 keV
spectrum. We suggest thermal Comptonisation of blackbody photons by a hot plasma
on the sur-face of the neutron star as the emission mechanism. The parameters of
the plasma are kT almost-equal-to 30 keV and optical depth tau almost-equal-to
2. The spectral shape of this model gives a good fit to the data and can explain
why observations at slightly different energy ranges mimic bremsstrahlung
spectra of different temperatures, since its shape can be approximated by
bremsstrahlung spectra of different temperatures in different energy intervals.
Marthon, P.,Bon, P.,Bruel, A.: 1983, Proceedings of the Society of Photo-Optical
Instrumentation Engineers, 312,148
Numerical-Method of Adapted Deconvolution - Application to the Tomography By
Coded Aperture
McConnell, M.L.,Dunphy, P.P.,Forrest, D.J.,Chupp, E.L.,Owens, A.: 1987,
Astrophysical Journal, 321,543
Gamma-Ray Observations of the Crab Region Using a Coded-Aperture Telescope
McConnell, M.L.,Forrest, D.J.,Chupp, E.L.,Dunphy, P.P.: 1982, IEEE Transactions
On Nuclear Science, 29,155
A Coded Aperture Gamma-Ray Telescope
A gamma ray telescope is being developed to operate in the energy range 100 keV
to 5 MeV utilizing coded aperture imaging. The design incorporates a mask
pattern based on a Uniformly Redundant Array (URA), which has been shown to have
ideal imaging characteristics. A mask anti-mask procedure is used to eliminate
the effects of any possible systematic variations in detector background rates.
The detector array is composed of 35 elements of the high-Z material Bismuth
Germanate (BGO). Results of laboratory testing of the imaging properties will be
presented. A southern hemisphere balloon flight is planned for 1982 with the
goal of observing the 0.511 MeV radiation from the Galactic Center. Computer
calculations show that a point source of this radiation can be located to within
+/- 1 degree.
McConnell, M.L.,Forrest, D.J.,Owens, A.,Dunphy, P.P.,Vestrand, W.T.,Chupp, E.L.:
1989, Astrophysical Journal, 343,317
Gamma-Ray Observations of Cygnus-X-1 and Cygnus-X-3 Using a Coded-Aperture
Telescope
Miyamoto, S.: 1977, Space Science Instrumentation, 3,473
Hadamard Transform X-Ray Telescope
A Hadamard transform X-ray telescope is a type of Dicke's random hole X-ray
camera for observing the X-ray sky. Instead of making a random pattern mask, a
cyclic Hadamard matrix or PN sequence is used to make the mask pattern for this
telescope. With this mask and a position sensitive X-ray detector, one can get
Hadamard transformed image data of the X-ray sky and easily reconstruct the X-
ray sky image from the observed data. The Hadamard matrix can be used to make
one dimensional X-ray telescope as well as two-dimensional telescopes. In the
case that spurious counts on the detector are predominant over image counts and
background counts, the SNR advantage of this telescope is sqrtN/2 compared to
the slat type X-ray telescope of the same angular resolution, where N is the
number of position sensitive detector cells and N+1 is the order of the cyclic
Hadamard matrix employed to make this mask.
Miyamoto, S.,Tsunemi, M.,Tsuno, K.: 1981, Nuclear Instruments & Methods in
Physics Research, 180,557
Some Characteristics of Hadamard Transform X-Ray Telescopes
The characteristics of the Hadamard transform X-ray telescope (HTXT) are
investigated and the following results are obtained: (1) the statistical error
of the image, reconstructed by the HTXT, is uniform all over the image, which is
different from the case of a pinhole camera. (2) The SNR of the HTXT is much
better than that of the pinhole camera in the case that spurious counts are
predominant over the counts due to the X-ray image. (3) The statistical error of
the image, which is obtained by summing of several image elements of an HTXT of
a finer angular resolution to get a fixed angular resolution is worse that
obtained by the HTXT which is designed to the final angular resolution
beforehand. (4) Even in the case that data of some detector cells are lost, the
image can be reconstructed. (5) All detector cells of the HTXT must see the same
X-ray image through the Hadamard mask, otherwise the error due to the
fluctuating number of mask holes is introduced. (6) The image reconstructed by
the HTXT becomes obscure by the amount of the positional resolution of the X-ray
detector in the case that the positional resolution is larger than the cell of
the detector. (7) The Hadamard transform imaging system described in this paper
is also applicable to other fields such as plasma and a medical diagnoses with
slight alteration of the system and is expected to have the same characteristics
as the HTXT.
Nelson, E.D.,Fredman, M.L.: 1970, Journal of the Optical Society of America, 60,
1664
Hadamard Spectroscopy
The basic concept of Hadamard spectroscopy is presented. General methods are
given for the construction of cyclic measurement matrices. A new algorithm,
which permits adaptation of the fast HAdamard transform to the calculation of
spectral intensities when the measurement matrices are cyclic, is introduced.
Some applications are also briefly discussed.
Neumann, D.R.,Flynn, M.J.,Gottschalk, S.,Wiener, S.N.: 1983, Journal of Nuclear
Medicine, 24,P25
Comparative Tomographic Imaging Performance of a Hybrid Coded-Aperture Parallel-
Plate Stationary Collimator and a Rotating Camera
Nottingham, M.R.: 1993, Ph.D. Thesis, University of Birmingham (UK)
X-Ray Observations of the Galactic Centre Utilising a New Analytical Technique
A new technique for the analysis of data from coded mask telescopes is
introduced. It is shown that this new technique called 'Maximum Likelihood
Fitting' (MALF), has several advantages over conventional techniques espacially
in the reduction of coding noise from the 'box cameras' design of coded mask
telescopes. The new technique is then used with data obtained by the TTM coded
mask instrument when the instrument was pointing in the direction of the
galactic centre region. Using the MALF technique it was possible to solve for
the intensity (in different energy channels) of the small scale (1 degree)
diffuse emission which is seen emanating from the galactic nucleus. This would
be the first time that accurate spectral measurements of this source have been
obtained, however no spatial information could be obtained as an assumed
distribution had to be used. All of the point sources which were in the field of
view of the instrument during the observations of the galactic centre were also
analysed using a variaty of spectral models to try and obtain as much
information about individual sources and also to investigate the differences
observed between the various groups of X-ray binaries.
Nottingham, M.R.,Skinner, G.K.,Willmore, A.P.,Borozdin, K.N.,Churazov, E.,
Sunyaev, R.A.: 1993, Astronomy & Astrophysics Supplement Series, 97,165
Observations of the Galactic-Center With the TTM Instrument
A new technique has been developed for the analysis of data from the TTM
instrument coded mask telescope. Preliminary spectral results are presented for
diffuse emission and point sources in the galactic centre.
Nugent, K.A.: 1987, Applied Optics, 26,563
Coded Aperture Imaging - A Fourier Space Analysis
Coded aperture imaging is analyzed in Fourier space and the conditions for
obtaining artifact-free 3-D images are obtained. It is deduced that an infinite
square array of coding apertures will obey these conditions. A finite array is
considered and it is shown that, after a certain coordinate transformation has
been performed, the finite aperture acts to bandlimit the spatial frequencies in
the image. This results is used to deduce a sampling theorem for coded apertures
which places limits on the artifact-free 3-D information that may be obtained.
It is thus deduced that 3-D information with a resolution greater than the
limits placed here may only be obtained by extrapolating the data to larger
viewing angles.
Nugent, K.A.: 1987, Optics Communications, 62,305
Maximum-Entropy Analysis of Coded Images
Nugent, K.A.: 1988, Review of Scientific Instruments, 59,1658
Coded Imaging of Thermonuclear Neutrons
Nugent, K.A.,Lutherdavies, B.: 1984, Optics Communications, 52,287
The Use of a Regular Array of Apertures in Penumbral Imaging
Nugent, K.A.,Lutherdavies, B.: 1986, Applied Optics, 25,1008
Potential and Limitations of Penumbral Imaging
Ohyama, N.,Endo, T.,Honda, T.,Tsujiuchi, J.,Matumoto, T.,Iinuma, T.A.,Ishimatsu,
K.: 1984, Applied Optics, 23,3168
Coded-Aperture Imaging-System for Reconstructing Tomograms of Human Myocardium
Ohyama, N.,Honda, T.,Tsujiuchi, J.: 1981, Optics Communications, 36,434
Tomogram Reconstruction Using Advanced Coded Aperture Imaging
Ohyama, N.,Honda, T.,Tsujiuchi, J.,Matumoto, T.,Iinuma, T.A.,Ishimatsu, K.:
1983, Applied Optics, 22,3555
Advanced Coded-Aperture Imaging-System for Nuclear-Medicine
Olmos, P.,Cid, C.,Bru, A.,Oller, J.C.,Depablos, J.L.,Perez, J.M.: 1992, Applied
Optics, 31,4742
Design of a Modified Uniform Redundant Array Mask for Portable Gamma Cameras
Uniform redundant-array masks have been reported as good lenses to form the
image of gamma sources, with the correlation between the mask-aperture matrix
and, the shadows projected on a static position-sensitive detector. We present a
modified uniform redundant-array configuration suitable for portable and small-
size gamma-cameras; its ability to reconstruct the image of several sources is
analyzed. We have carried out a Montecarlo simulation of the gamma interactions
in the mask, defining the expected response of the correlation process and
comparing it with that achieved with the usual uniform redundant-array
configurations.
Owens, A.: 1990, Nuclear Instruments & Methods in Physics Research Section A-
Accelerators Spectrometers Detectors and Associated Equipment, 292,706
Limiting Sensitivities of Coded-Aperture Telescopes for Gamma-Ray Astronomy -
Balloon-Borne Fixed-Mask Systems
Palmer, D.M.,Schindler, S.M.,Cook, W.R.,Grunsfeld, J.M.,Heindl, W.A.,Prince,
T.A.,Stone, E.C.: 1993, Astrophysical Journal, 412,203
Gamma-Ray Continuum and Line Observations of SN 1987a
The Caltech gamma-ray imaging telescope observed the hard X-ray and gamma-ray
emission from SN 1987A as it evolved between 1987 May and 1989 April, in a
series of four balloon flights from Alice Springs, NT, Australia. Observations
of the Crab Nebula and Pulsar provided in-flight data on pointing accuracy and
instrument function for each flight. Results presented here include our
measurements on 1987 November 18 (D268) and 1988 April 12 (D414) of both line
emission at 847 and 1238 keV from the decay of Co-56, and Compton-scattered
continuum above 50 keV. Upper limits for both line and continuum emission were
obtained on 1987 May 20 (D86) and 1989 April 4 (D771). For the D268 and D414
continuum measurements, our results are best-fit by a differential power law of
the form dN/dE = kappaE(-gamma)(cm-2 s-1 keV-1) for the energy range 50-800 keV.
Our corresponding line measurements were fit with Gaussian profiles, containing
additional terms for the underlying continuum. We compare our flux measurements
and upper limits to those from other experiments and to predictions of
theoretical models.
Palmieri, T.M.: 1974, Astrophysics and Space Science, 28,277
Multiplex Methods and Advantages in X-Ray Astronomy
The multiplex advantage is defined and applied in considering various techniques
presently used in X-ray astronomy. It is concluded that the multiplex advantage
will be useful in evaluating future techniques to be used in X-ray astronomy.
Palmieri, T.M.: 1974, Astrophysics and Space Science, 26,431
An X-Ray Telescope Sensitive At High Energies
A telescope is described which is capable of producing images of point sources
of x-rays without recourse to reflection optics. A mathematical approach to the
operation and to the SNR properties of the telescope is presented. This is
followed by several examples of its response and a discussion of detectors that
could be used with the device.
Pan, H.C.,In 't Zand, J.J.M.,Skinner, G.K.,Borozdin, K.N.,Gilfanov, M.R.,Sunyaev,
R.A.: 1993, Astronomy & Astrophysics Supplement Series, 97,273
Observations of X-Ray Transient Source GS2023+338 With the TTM Coded Mask
Telescope
We present results from TTM observations in which we monitored the bright X-ray
transient source GS2023+338 (= V404 Cyg) in the period 1989 June-August.
Park, J.B.,Johnson, T.W.,Dyer, S.A.,Harms, B.K.,Dyer, R.A.: 1990, Applied
Spectroscopy, 44,219
On the Mean-Square Error of Various Spectrum-Recovery Techniques in Hadamard-
Transform Spectrometry
Pasedach, K.,Haase, E.: 1981, Optics Communications, 36,423
Random and Guided Generation of Coherent 2-Dimensional Codes
Patterson, T.G.: 1990, Ph.D. Thesis, University of Birmingham
A Survey of the Galactic Bulge, Large Magellanic Cloud and Cygnus Region With A
Simple Configuration Coded Mask X-Ray Telescope
Paul, J.,Lebrun, F.,Mandrou, P.,Roques, J.P.: 1993, Acta Astronautica, 30,261
2 Years of Successful Operations of the Coded-Mask Telescope Sigma for Hard X-
Ray and Soft Gamma-Ray Astronomy
At the beginning of the previous decade, it was recognized that a possible means
of improving existing hard X-ray and gamma-ray telescopes, where focusing
techniques are totally impracticable, is the incorporation of the coded-aperture
technique to actually image celestial sources. The primary advantage of such a
technique is to maintain the angular resolution of a single pinhole camera,
while increasing the overall effective area of the instrument. Moreover, the
coded-mask principle includes the simultaneous measurement of the sky and
detector background, systematic effects due to temporal variations in the
background are removed. This paper reports on the French SIGMA telescope, the
first coded-aperture telescope sensitive to radiation in the energy range from
35 KeV to 1.3 MeV to be operated in space. The SIGMA telescope is one of the
main devices on board the astronomy satellite GRANAT, successfully launched on
December 1, 1989 from Baikonour, Kazakhstan. After a comprehensive description
of the instrument, a report is given on the most relevant inferences which can
be drawn from two years of successful in-orbit operations, in order to better
define the next generation of gamma-ray instruments.
Paxman, R.G.,Barrett, H.H.,Smith, W.E.: 1985, Acta Polytechnica Scandinavica-
Applied Physics Series,,285
Object Dependent System-Design in Coded-Aperture Imaging
Paxman, R.G.,Barrett, H.H.,Smith, W.E.,Milster, T.D.: 1985, Journal of the
Optical Society of America A-Optics Image Science and Vision, 2,501
Image-Reconstruction from Coded Data .2. Code Design
Paxman, R.G.,Gindi, G.R.,Barrett, H.H.: 1982, Journal of the Optical Society of
America, 72,1737
Tomography With Coded Apertures - The Case for Continuous Objects
Paxman, R.G.,Smith, W.E.,Barrett, H.H.: 1984, Journal of Nuclear Medicine, 25,
700
2 Algorithms for Use With an Orthogonal-View Coded-Aperture System
Pearson, D.,Pillai, S.U.,Lee, Y.J.: 1990, IEEE Transactions On Information
Theory, 36,1280
An Algorithm for Near-Optimal Placement of Sensor Elements
Ponman, T.J.,Bertram, D.,Church, M.J.,Eyles, C.J.,Watt, M.P.,Skinner, G.K.,
Willmore, A.P.: 1990, Nature, 347,450
The Distribution of Iron in the Perseus Cluster
Ponman, T.J.,Hammersley, A.P.,Skinner, G.K.: 1987, Nuclear Instruments & Methods
in Physics Research, A262,419
Error Analysis for a Noncyclic Imaging System
The imaging properties of the `coded aperture box camera', a noncyclic coded
mask system in which mask and detector are the same size, are investigated under
the assumption of random positioning of the mask holes. Each source in the field
of view generates noise due to the imperfect coding, in addition to the Poisson
and detector noise present in a cyclic coded mask imager. Equations are
presented for the magnitude and spatial variation of each of these three sources
of noise, and their validity is confirmed by simulations. For a small number of
sources the coding variance from each can simply be superposed to a good
approximation. In the case of many sources the coding variance is less than the
superposition value. The box camera has advantage over a collimated cyclic
imager, particularly for wide field imaging, provided that coding errors are not
too large compared to Poisson and detector noise.
Proctor, R.J.,Skinner, G.K.,Willmore, A.P.: 1979, Monthly Notices of the Royal
Astronomical Society, 187,633
The Design of Optimum Coded Mask X-Ray Telescopes
Considerations involved in the construction and operation of an optimum coded-
mask X-ray telescope are discussed. The coded-mask imaging technique is
described, along with mask design and construction, telescope geometry, the
detector in a coded-mask telescope, attitude determination and control, and data
analysis. Specific attention is given to the SL 1501 coded-mask telescope and
results obtained with that instrument. It is shown that all the problems
associated with the design of coded-mask telescopes are soluble and that X-ray
images can be produced at wavelengths shorter than those that can be handled
with grazing-incidence optics.
Ranieri, M.,Badiali, M.,Cardini, D.,Emanuele, A.,Auriemma, G.: 1981, Journal of
the British Interplanetary Society, 34,135
Coded Aperture Telescopes for Hard X-Ray Astronomy
The coded aperture signal processing reconstruction technique, and its
application to a balloon-borne hard X-ray and gamma-burst telescope useful for
high-resolution mapping where numerous X-ray sources are present, are described.
The coded mask principle, telescope design, background noise, and detector
specifications are discussed, as are the results of a Monte Carlo computer
simulation of the system.
Ress, D.,Bell, P.M.,Bradley, D.K.: 1993, Review of Scientific Instruments, 64,
1404
A Time-Resolved X-Ray Ring Coded-Aperture Microscope for Inertial Confinement
Fusion Applications
For energetic x rays (hv greater-than-or-equal-to 3 keV), ring coded-aperture
imaging gives better signal-to-noise ratio than equivalent-resolution pinhole
cameras for inertial confinement fusion (ICF) targets. We have created a time-
resolved ring coded-aperture microscope by combining a 4 X 3 array of annular
apertures with a gated microchannel-plate x-ray imager. The new instrument can
produce 500-ps duration sequences of images with a temporal resolution of 80 ps
and a spatial resolution of 5 to 6 mum. In demonstration experiments, coded
images of imploded targets directly driven by the Omega laser at the Laboratory
for Laser Energetics showed the formation and dissolution of the target cores
with improved detail. Contour plots of the images indicate that the laser
illumination pattern is imprinted in the imploded core region. The gated ring-
aperture microscope will be useful in detailed studies of ICF target
hydrodynamics.
Rogers, W.L.,Adller, R.S.: 1982, Applied Optics, 21,324
Time-Coded Aperture Design for Nuclear-Medicine Imaging - A Study of Signal-To-
Noise Ratio
Roques, J.P.: 1987, Applied Optics, 26,3862
Fast Decoding Algorithms for Uniformly Redundant Arrays
Coded mask aperture imaging techniques are now used in various fields, in
particular in X-ray and gamma-ray astronomy. With such systems it is possible to
construct apertures which have autocorrelation functions with perfectly flat
sidelobes. For quadratic residue arrays (URAs), we have developed fast
deconvolution algorithms based on conventional decoding methods but taking
advantage of the mathematical properties of the decoding matrices. Balanced
decoding, delta decoding, and finely sampled decoding are discussed.
Ruf, C.S.: 1993, IEEE Transactions On Antennas and Propagation, 41,85
Numerical Annealing of Low-Redundancy Linear Arrays
An algorithm is developed that estimates the optimal distribution of antenna
elements in a minimum redundancy linear array. These distributions are used in
thinned array interferometric imagers to synthesize effective antenna apertures
much larger than the physical aperture. The optimal selection of antenna
locations is extremely time consuming when large numbers of antennas are
involved. This algorithm uses a numerical implementation of the annealing
process to guide a random search for the optimal array configuration. Highly
thinned low-redundancy arrays are computed for up to 30 array elements. These
arrays are equivalent to the optimal solutions that are known for up to 11
elements. The arrays computed for 12-30 elements have the least redundancies
reported to date.
Rothschild, R.E., Matteson, J.L., Heindl, W.A., et al.: 1995
SPIE
The Continuous Hard X-ray Imager for Astrophysics (CHIP)
(proposed coded aperture imaging mission between 2 and 100 keV with CdZnTe
detectors and an array of flat coded apertures)
Salotti, L.,Ballet, J.,Cordier, B.,Lambert, A.,Bonazzola, S.,Mereghetti, S.,
Mandrou, P.,Roques, J.P.,Sunyaev, R.,Gilfanov, M.,Churazov, E.,Chulkov, I.,
Kuznetsov, A.,Dyachkov, A.,Khavenson, N.,Novikov, B.: 1992, Astronomy and
Astrophysics, 253,145
Soft Gamma-Ray Observations of Cygnus X-1 With the Coded-Aperture Sigma
Telescope
The galactic black-hole candidate Cygnus X-1 was observed by the soft gamma ray
orbiting SIGMA telescope during March 23/24, 1990. This coded-aperture
instrument records images of the sky in the 35 keV-1.3 MeV energy range. Data
have been collected in imaging mode and in fast-timing mode. In about one day of
image accumulation the source has been detected up to almost-equal-to 500 keV
with high statistical significance. The derived photon spectrum has been fitted
with various analytical shapes. The best fit corresponds to a Comptonized model
with an electron temperature of kT(e) = 62.3 +/- 4.5 keV and an optical depth
tau = 2.02 +/- 0.13. Our flux value at 100 keV, combined with simultaneous X-ray
measurements, suggests that the source was in a typical gamma-2 state. Timing
data, which benefit from the millisecond resolution, have been analysed in order
to confirm the variability down to short timescales (80 ms) already detected by
HEAO-1 (Nolan et al. 1981b). Shot-noise behaviour has been detected even for E >
80 keV.
Seidler, P.: 1981, Electronics Letters, 17,96
Mismatched Filtering for Coded Aperture Imaging With Minimum Sidelobes
Sembay, S.,Gehrels, N.: 1990, Nuclear Instruments & Methods in Physics Research
Section A-Accelerators Spectrometers Detectors and Associated Equipment, 295,
477
Design Criteria for Small Coded Aperture Masks in Gamma-Ray Astronomy
Silva, R.,Rogers, G.L.: 1981, Optica Acta, 28,1125
Coded Aperture Imaging - A Noncoherent Optical Approach
Silva, R.,Rogers, G.L.: 1981, Pattern Recognition, 14,3
Coding and Decoding Pictures in Nuclear-Medicine
Silva, R.,Rogers, G.L.: 1982, Optica Acta, 29,257
Tomographical Possibilities in Coded Aperture Imaging Optical Simulations
Sims, M.: 1981, Ph.D. Thesis, University of Leicester
A Wide Field Camera for X-Ray Astronomy
Sims, M.,Turner, M.J.L.,Willingale, R.: 1980, Space Science Instrumentation, 5,
109
A Wide Field X-Ray Camera
A Wide Field of View Camera based on the Dicke or Coded Mask principle is
described. It is shown that this type of instrument is more sensitive than a
pinhole camera, or than a scanning survey of a given region of sky for wide
field conditions. The design of a practical camera is discussed and the
sensitivity and performance of the chosen design are evaluated by means of
computer simulations. The Wiener Filter and Maximum Entropy Methods of
deconvolution are described and these methods are compared with each other and
cross-correlation using data from the computer simulations. It is shown that the
analytic expressions for sensitivity used by other workers are confirmed by the
simulations, and that ghost images caused by incomplete coding can be
substantially eliminated by the use of the Wiener Filter and the MAximum Entropy
Method, with some penalty in computer time for the latter. The cyclic mask
configuration is compared with the simple mask camera. It is shown that when the
diffuse X-ray background dominates, the simple system is more sensitive and has
the better angular resolution. When sources dominate the simple system is less
sensitive. It is concluded that the simple coded mask camera is the best
instrument for wide field imaging of the X-ray sky.
Sims, M.,Turner, M.J.L.,Willingale, R.: 1985, Nuclear Instruments & Methods in
Physics Research, 228,512
The Influence of Disturbing Effects On the Performance of a Wide Field Coded
Mask X-Ray Camera
The coded aperture telescope, or Dicke camera, is seen as an instrument suitable
for many applications in X-ray and gamma ray imaging. In this paper the effects
of a partially obscuring window mask support or collimator, a detector with
limited spatial resolution, and motion of the camera during image integration
are considered using a computer simulation of the performance of such a camera.
Cross correlation and the Wiener filter are used to deconvolve the data. It is
shown that while these effects cause a degradation in performance this is in no
case catastrophic. Deterioration of the image is shown to be greatest where
strong sources are present in the field of view and is quite small (~10%) when
diffuse background is the major element. A comparison between the cyclic mask
camera and the simple mask camera is made under various conditions and it is
shown that the simple mask camera has a moderate advantage particularly when
imaging a wide field of view.
Sims, M.R.,Willingale, R.,Turner, M.J.L.: 1984, Nuclear Instruments & Methods in
Physics Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 221,77
Computer-Simulations of the Performance of Practical Designs of Coded Aperture
Cameras
The coded aperture camera is an instrument suitable for many applications in X-
and gamma-ray imaging. In this paper the effect of a partially obscuring window
support is considered using a computer simulation technique. This allows the
signal to noise in the decoded image to be evaluated for practical designs of
camera, a process which is difficult to carry out using an analytical approach.
The sensitivity of simple and cyclic forms of camera is determined for real
celestial X-ray source distributions under both source and diffuse background
dominated conditions. The image obtained is shown to be degraded but not
destroyed by the interference of the window support, and the simple form of
camera is shown to be more sensitive than the cyclic form for wide fields of
view.
Skinner, G.K.: Sept. 1980, Journal of the British Interplanetary Society, 33,
333
Imaging of Cosmic X-Ray Sources Using Coded Mask Telescopes
Mask designs which can be used for coded mask telescopes are discussed, and
methods of recovering the image are considered. The paper compiles information
from different fields and shows how the data is useful in the construction and
application of telescopes for X-ray astronomy. The description of a large dual
telescope system which is being constructed for flight on the Spacelab 2 mission
of the Space Shuttle is included.
Skinner, G.K.: 1984, Nuclear Instruments & Methods in Physics Research Section
A-Accelerators Spectrometers Detectors and Associated Equipment, 221,33
Imaging With Coded-Aperture Masks
Coded-MAsk imaging systems may be considered as generalizations of the pinhole
camera in which the `coding-plane' contains a carefully chosen pattern of
transparent and opaque regions instead of a single pinhole. A variety of
instruments result from selecting different coding patterns and from simple
geometrical variations on the theme. The various schemes which have been
proposed and used and the methods of interpreting the data obtained with them
are reviewed and compared. Emphasis is placed on systems for X-ray astronomy.
Skinner, G.K.: 1988, Scientific American, 259,84
X-Ray-Imaging With Coded Masks
Skinner, G.K.,Eyles, C.J.,Willmore, A.P.,Bertram, D.,Church, M.J.,Herring,
J.R.H.,Ponman, J.,Watt, M.P.: 1988, Astrophysical Letters & Communications, 27,
199
The Spacelab-2 X-Ray Telescope - Coded Mask Imaging in Orbit
Skinner, G.K.,Foster, A.J.,Willmore, A.P.,Eyles, C.J.: 1990, Monthly Notices of
the Royal Astronomical Society, 243,72
Localization of One of the Galactic-Center X-Ray Burst Sources
Skinner, G.K.,Grindlay, J.E.: 1993, Astronomy and Astrophysics, 276,673
Coded Masks With 2 Spatial Scales
A new design is proposed for masks for wide-band coded aperture X-ray/gamma-ray
telescopes. The masks contain both elements with a coarse spatial scale, which
are opaque at all energies at which the telescope is to operate, and elements
with finer structure which provide good angular resolution at low energies but
which become transparent in the upper part of the energy range. It is shown that
patterns exist which have very satisfactory imaging properties and that the
sensitivity which is sacrificed to obtain the improvement in angular resolution
is very small, even at intermediate energies where the fine mask is partially
absorbing.
Skinner, G.K.,Harper, P.K.S.,Herring, J.R.H.,Ramsey, B.D.: 1988, Nuclear
Instruments & Methods in Physics Research Section A-Accelerators Spectrometers
Detectors and Associated Equipment, 273,682
The Spacelab 2 Xrt Xenon-Filled Position-Sensitive Proportional-Counters
Skinner, G.K.,Nottingham, M.R.: 1993, Nuclear Instruments & Methods in Physics
Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 333,540
Analysis of Data from Coded-Mask Telescopes By Maximum-Likelihood
Coded mask telescopes have proved of great utility in X- and gamma-ray
astronomy. A coded mask telescope of a non-cyclic ''box-camera'' design can in
some circumstances have a sensitivity advantage over an optimally coded cyclic
configuration, but images reconstructed by a simple correlation technique are
subject to various imperfections. A new method, maximum likelihood fitting
(MALF), for the analysis of data from non-cyclic coded mask telescopes is
presented. MALF avoids artifacts due to strong sources and handles in an optimum
way data affected by small-number statistics, by partial coding and by aspects
of real systems such as finite detector depth and obscurations of parts of the
detector.
Skinner, G.K.,Pan, H.C.,Maisack, M.,Staubert, R.,Borozdin, K.N.,Brinkman, A.C.,
Englhauser, J.,Gilfanov, M.R.,Kaniovsky, A.C.,Pietsch, W.,Sunyaev, R.A.,In 't Zand,
J.J.M.: 1991, Astronomy and Astrophysics, 252,172
The Spectrum and Position of the Hard Galactic-Center Source 1E1740.7-2942
The remarkable hard X-ray and gamma-ray source close to the galactic centre, 1E
1740.7-2942, was observed with two of the instruments of the Rontgen Observatory
on the Kvant module of MIR. We present observations made with the TTM coded-mask
imager and the HEXE phoswich instrument which together provide spectral coverage
from approximately 2 to 200 keV. The spectrum can be well described by a hard
power-law with a high energy cut-off and absorption at low energies.
Similarities with the spectra of Cyg X-1 and other black hole candidates suggest
that 1 E1740.7-2942 may, too, be a black hole binary. With a view to
establishing the counterpart of this source in other wavebands, the position of
this source was determined with an uncertainty of 12", a significant improvement
on the precision of earlier measurements. We consider constraints on the nature
of the source imposed by limits on optical and near IR objects within the new
error circle.
Skinner, G.K.,Ponman, T.J.: 1987, Journal of the British Interplanetary Society,
40,169
Coded Mask Telescopes for X-Ray Astronomy
The Department of Space Research has made extensive use of coded mask
techniques, many aspects of which were pioneered in Birmingham. We describe here
the technique and some instruments using it. (Author abstract) 8 refs.
Skinner, G.K.,Ponman, T.J.: 1994, Monthly Notices of the Royal Astronomical
Society, 267,518
On the Properties of Images from Coded-Mask Telescopes
We consider coded-mask telescopes with cyclic mask patterns that are 'optimum',
i.e. patterns that are based on uniformly redundant arrays (URAs), which can be
derived using cyclic difference sets. The properties of images obtained with
different reconstruction arrays are compared to find the best options. In the
usual case where the detector background is imperfectly known, it is easily
shown that, although the elements of an image reconstructed by any of the usual
algorithms are nearly independent of each other and of the detector background,
they cannot be perfectly so. The correlation between image elements that results
is evaluated for various reconstruction algorithms and the circumstances in
which it may be important are discussed. Although the effect is small when point
sources are considered, it may be significant where sources of emission cover an
appreciable fraction of the field of view. Masks based on 'modified URAs' lead
to slightly worse interdependence of image pixels.
Skinner, G.K.,Ponman, T.J.,Hammersley, A.P.,Eyles, C.J.: 1987, Astrophysics and
Space Science, 136,337
Techniques for the Analysis of Data from Coded-Mask X-Ray Telescopes
Several techniques useful in the analysis of data from coded-mask telescopes are
presented. Methods of handling changes in the instrument pointing direction are
reviewed and ways of using FFT techniques to do the deconvolution considered.
Emphasis is on techniques for optimally-coded systems, but it is shown that the
range of systems included in this class can be extended through the new concept
of 'partial cycle averaging'.
Skinner, G.K.,Willmore, A.P.,Eyles, C.J.,Bertram, D.,Church, M.J.,Harper,
P.K.S.,Herring, J.R.H.,Peden, J.C.M.,Pollock, A.M.T.,Ponman, T.J.,Watt, M.P.:
1987, Nature, 330,544
Hard X-Ray Images of the Galactic-Center
Skinner, G.K.,Willmore, A.P.,Eyles, C.J.,Bertram, D.,Church, M.J.,Harper,
P.K.S.,Herring, J.R.H.,Peden, J.C.M.,Pollock, A.M.T.,Ponman, T.J.,Watt, M.P.:
1987, Nature, 330,544
Hard X-Ray Images of the Galactic-Center
Smith, W.E.,Barrett, H.H.: 1988, Journal of the Optical Society of America A-
Optics Image Science and Vision, 5,315
Linear-Estimation Theory Applied to the Evaluation of A-Priori Information and
System Optimization in Coded-Aperture Imaging
Smith, W.E.,Barrett, H.H.,Paxman, R.G.: 1983, Optics Letters, 8,199
Reconstruction of Objects from Coded Images By Simulated Annealing
Smith, W.E.,Barrett, H.H.,Paxman, R.G.: 1984, Journal of Nuclear Medicine, 25,
P55
The Consequences of Multiplexing and Limited View Angle in Coded-Aperture
Imaging
Smith, W.E.,Paxman, R.G.,Barrett, H.H.: 1985, IEEE Transactions On Nuclear
Science, 32,758
Application of Simulated Annealing to Coded-Aperture Design and Tomographic
Reconstruction
Smith, W.E.,Paxman, R.G.,Barrett, H.H.: 1985, Journal of the Optical Society of
America A-Optics Image Science and Vision, 2,491
Image-Reconstruction from Coded Data .1. Reconstruction Algorithms and
Experimental Results
Stalker, K.T.,Kelly, J.G.: 1981, Proceedings of the Society of Photo-Optical
Instrumentation Engineers, 294,135
Design of a Coded Aperture Imaging-System for Simulated Reactor Accident
Experiments
Steer, D.G.,Dewdney, P.E.,Ito, M.R.: 1984, Astronomy and Astrophysics, 137,159
Enhancements to the Deconvolution Algorithm Clean
Steinbach, A.,Macovski, A.: 1979, Journal of Physics D, 12,2079
Improved Depth Resolution With One Dimensional Coded Aperture Imaging
Stephen, J.B.,Caroli, E.,Dicocco, G.,Maggioli, P.P.,Natalucci, L.,Spizzichino,
A.: 1987, Astronomy and Astrophysics, 185,343
The Identification of Vignetted Sources in Coded Aperture Imaging
The next generation of gamma-ray telescopes will utilize the technique of coded
apertures in order to provide high resolution images of the celestial sphere.
This method, however, suffers from a disadvantage wherein vignetted sources are
reconstructed in false positions with incorrect intensities. Most techniques of
identifying these sources involve the use of time consuming iterative computer
algorithms. One recent suggestion, however, allows fast decoding which is also
accurate when there are a limited number of sources in the field of view and a
high background level, as is the case for contemporary low energy gamma-ray
instruments. This method has been examined in detail by means of Monte Carlo
simulation in order to assess its accuracy and sensitivity.
Stroke, G.W.: 1968, Physics Letters, 28A,252
A New Class of Optical Imaging Systems Achieving 'Aperture Synthesis' from Non-
Conventional Optics By a Posteriori Lensless Fourier Transform Holography
Stroke, G.W.,Hayat, G.S.,Hoover, R.B.,Underwood, J.H.: 1969, Optics
Communications, 1,138
X-Ray Imaging With Multiple-Pinhole Cameras Using a Posteriori Holographic Image
Synthesis
Sunyaev, R.,Churazov, E.,Gilfanov, M.,Terekhov, O.,Dyachkov, A.,Khavenson, N.,
Kovtunenko, V.,Kremnev, R.,Claret, A.,Lebrun, F.,Goldwurm, A.,Paul, J.,Pelaez,
F.,Atteia, J.L.,Mandrou, P.,Vedrenne, G.: 1993, Astronomy & Astrophysics
Supplement Series, 97,85
A Search for Weak Gamma-Ray Bursts With Granat/Sigma
During more than two years of GRANAT mission, the Gamma Ray Burst (GRB) cell of
the narrow-aperture coded mask telescope SIGMA was operated for approximately
5300 hours (see Sunyaev et al., 1992a for more details). The coding system of
SIGMA is capable of localizing to within arcmin accuracy the GRB events detected
in the 18.1-degrees by 16.8-degrees coded field of view. Inspite of the high
sensitivity of the cell to the on-axis events (3 x 10(-8) and 8 x 10(-8) erg/cm2
in the 40-90 keV band for 0.25 and 2.0 sec integration time) no bursts were
actually found within the coded field of view. For about 950 hours SIGMA was
pointed towards the Galactic Center (GC) and more than 1.5 x 10(10) M. of
Galactic matter was within the telescope coded FOV. For an object placed at 8.5
kpc distance, the threshold burst luminosity in the 40-90 keV band
(approximately 3 X 10(38) erg/sec) is comparable with the Eddington limit for a
neutron star. The absence of weak GRB events from the GC direction indicates
that either the luminosity of a typical GRB is below approximately 10(38) ergs/
sec and GRB are of local origin or, alternatively, that the luminosity is as
high as approximately 10(40) ergs/sec or greater and most of GRB come from a
massive Galactic ''hale or are of cosmological origin. The lack of weak GRB
events observed by SIGMA from all directions is inconsistent with an
extrapolation of the KONUS data if the integral GRB counts slope is -3/2.
Sunyaev, R.,Kaniovsky, A.,Efremov, V.,Gilfanov, M.,Churazov, E.,Grebenev, S.,
Kuznetsov, A.,Melioranskiy, A.,Yamburenko, N.,Yunin, S.,Stepanov, D.,Chulkov,
I.,Pappe, N.,Boyarskiy, M.,Gavrilova, E.,Loznikov, V.,Prudkoglyad, A.,Rodin, V.,
Reppin, C.,Pietsch, W.,Engelhauser, J.,Trumper, J.,Voges, W.,Kendziorra, E.,
Bezler, M.,Staubert, R.,Brinkman, A.C.,Heise, J.,Mels, W.A.,Jager, R.,Skinner,
G.K.,Alemam, O.,Patterson, T.G.,Willmore, A.P.: 1987, Nature, 330,227
Discovery of Hard X-Ray-Emission from Supernova-1987a
Sunyaev, R.A.,Kaniovsky, A.S.,Borozdin, K.N.,Efremov, V.V.,Arefev, V.A.,
Melioransky, A.S.,Skinner, G.K.,Pan, H.C.,Kendziorra, E.,Maisack, M.,
Doebereiner, S.,Pietsch, W.: 1993, Astronomy and Astrophysics, 280,L1
Broad-Band X-Ray Observations of the GRO-J0422+32 X-Ray Nova By the Mir-Kvant
Observatory
Observations of GRO J0422+32 X-Ray Nova with the instruments of the ''Mir-
Kvant'' observatory show that the X-ray spectrum is similar to that of the well-
known black-hole candidate Cyg X-1 in its ''low'' state. In the standard 2-20
keV X-ray range both have power law spectra with no strong soft component while
at energies higher than 100 keV an exponential cutoff is clearly seen in the
spectrum in both cases. Such cutoffs are typical of thermal comptonization of
low-frequency photons in the high-temperature plasma of accretion disks.
Syunyaev, R.A.,Arefev, V.A.,Borozdin, K.N.,Gilfanov, M.R.,Efremov, V.V.,
Kaniovskii, A.S.,Churazov, E.M.,Kendziorra, E.,Mony, B.,Kretschmar, P.,Maisack,
M.,Staubert, R.,Dobereiner, S.,Englhauser, J.,Pietsch, W.,Reppin, C.,Trumper,
J.,Skinner, G.K.,Nottingham, M.R.,Pan, H.,Willmore, A.P.: 1991, Soviet Astronomy
Letters, 17,409
Broad-Band X-Ray-Spectra of Black-Hole Candidates, X-Ray Pulsars, and Low-Mass
Binary-X-Ray Systems - Kvant Module Results
The broadband spectra of the brightest x-ray sources obtained by the TTM, Hexe,
and Pulsar X-1 instruments of the Kvant module demonstrate differences in the
hardness of the spectrum of the weak magnetic field neutron star Sco X-1, the x-
ray pulsars A 0535 + 26, Vela X-1, and LMC X-4, and the blackhole candidates Cyg
X-1, GS 2023 + 338, GS 2000 + 25, and 3C 273.
Syunyaev, R.,Gilfanov, M.,Churazov, E.,Loznikov, V.,Yamburenko, N.,Skinner,
G.K.,Patterson, T.G.,Willmore, A.P.,Emam, O.,Brinkman, A.C.,Heise, J.,In 't Zand,
J.J.M.,Jager, R.: 1990, Soviet Astronomy Letters, 16,59
The New X-Ray Transient Burster KS1731-260
Syunyaev, R.,Gilfanov, M.,Churazov, E.,Loznikov, V.,Yamburenko, N.,Skinner,
G.K.,Patterson, T.G.,Willmore, A.P.,Emam, O.,Brinkman, A.C.,Heise, J.,In 't Zand,
J.J.M.,Jager, R.: 1990, Soviet Astronomy Letters, 16,55
X-Ray Observations of the Large Magellanic Cloud By the TTM Telescope On Board
the Kvant Module from November 1988 to June 1989
Syunyaev, R.A.,Gilfanov, M.R.,Churazov, E.M.,Yamburenko, N.S.,Brinkman, A.C.,
Heise, J.,In 't Zand, J.J.M.,Jager, R.,Skinner, G.K.,Alemam, O.,Patterson, T.G.,
Willmore, A.P.: 1988, Soviet Astronomy Letters, 14,296
Stabilization of Mir-Kvant - The TTM X-Ray Data
Syunyaev, R.A.,Gilfanov, M.R.,Churazov, E.M.,Yamburenko, N.S.,Brinkman, A.C.,
Heise, J.,In 't Zand, J.J.M.,Jager, R.,Skinner, G.K.,Alemam, O.,Patterson, T.G.,
Willmore, A.P.: 1988, Soviet Astronomy Letters, 14,252
Upper Limits On the 2-32 Kev Emission of Supernova-1987a in June August 1987
Syunyaev, R.A.,Kaniovskii, A.,Efremov, V.,Gilfanov, M.,Churazov, E.,Grebenev,
S.A.,Kuznetsov, A.V.,Melioranskii, A.S.,Yamburenko, N.S.,Yunin, S.,Stepanov, D.,
Chulkov, I.,Pappe, N.,Boyarskii, M.N.,Gavrilova, E.A.,Loznikov, V.M.,
Prudkoglyad, A.,Rodin, V.G.,Reppin, C.,Pietsch, W.,Engelhauser, J.,Trumper, J.,
Voges, W.,Kendziorra, E.,Bezler, M.,Staubert, R.,Brinkman, A.C.,Skinner, G.K.,
Alemam, O.,Patterson, T.G.,Willmore, A.P.,Heise, J.,Mels, W.A.,Jager, R.: 1987,
Soviet Astronomy Letters, 13,431
Detection of Hard X-Rays from Supernova 1987a - Preliminary Mir-Kvant Results
Teegarden, B.J.,Cline, T.L.,Gehrels, N.,Porreca, G.,Tueller, J.,Leventhal, M.,
Huters, A.F.,MacCallum, C.J.,Stang, P.D.: 1985, Proc Nth Cosmic Ray Conference;
OG9.2, OG9.2,307
The Gamma-Ray Imaging Spectrometer (GRIS): A New Balloon-Bornne Experiment for
Gamma-Ray Line Astronomy
Ubertini, P.: 1993, Astronomy & Astrophysics Supplement Series, 97,389
X-Ray Monitor On Integral - Astrophysics in the 4-100 Kev Band
The X-Ray Monitor on INTREGAL will provide images with arcminute angular
resolution in the 4-100 keV band, simultaneously with the main gamma ray
instruments. The limiting sensitivity for a typical 10(5) second observation
will be better than one millicrab. The baseline photon detection system is a
high pressure imaging proportional counter behind a coded mask (focal length 4
meters; FOV 6 degrees FWHM to match the other instruments). In addition to its
support role on INTEGRAL (providing fine imaging and simultaneous X-Ray flux
measurements) the spectral resolution and sensitivity are sufficient to make it
a useful stand-alone instrument. In particular it will be able to monitor the
iron lines seen in both Galactic and extra-Galactic sources, and relate these to
the behavior of the hard continuum, seen in the other instruments. It will also
enable the study of hard X-Ray continua of many Galactic and extra-Galactic
sources: specifically the search for cyclotron lines in Galactic binaries,
Compton 'humps', and other features in AGN spectra, perhaps evidence for pair
processes. Because of its high sensitivity it will be used to scan the Galactic
plane once every few days to detect the onset of transients (potential 'hard
tail' objects), which can then be observed in detail by the Gamma ray
instruments.
Vangiessen, J.W.,Viergever, M.A.,Degraaf, C.N.: 1986, IEEE Transactions On
Medical Imaging, 5,222
Time-Coded Aperture Tomography - Experimental Results
Vertatschitsch, E.J.,Haykin, S.: 1991, IEEE Transactions On Antennas and
Propagation, 39,576
Impact of Linear-Array Geometry On Direction-Of-Arrival Estimation for a Single
Source
The impact of the linear array geometry on the direction of arrival estimation
accuracy is examined assuming a single source of illumination and additive white
Gaussian system noise. The analysis was conducted using the Cramer-Rao lower
bound (CRLB), simulation and performance modeling of maximum likelihood
estimation (MLE). Particular attention is paid to the implementation of the MLE,
the threshold signal-to-noise ratio (SNR), probability of outlier and high SNR
mean-squared error (MSE) performance which are evaluated and compared for
uniform and nonuniform arrays. The conditions under which trade-offs exist in
choosing a particular geometry and their significance are determined.
Villa, G.,Bussini, A.,Perotti, F.,Santambrogio, R.,Rampini, A.,Dicocco, G.,
Butler, R.C.,Caroli, E.,Stephen, J.B.,Traci, A.,Donati, A.,Ubertini, P.,
Lapadula, C.,Mastropietro, M.,Patriarca, R.,Dean, A.J.,Court, A.J.,Younis, F.A.,
Maggioli, P.,Yearworth, M.,Graham, G.: 1987, IEEE Transactions On Nuclear
Science, 34,26
The Structure of the Zebra Telescope, the Integration Tests and the 1st
Calibration Results
Villela, T.,Braga, J.,Damico, F.,Jayanthi, U.B.,Neri, J.A.: 1994, Astrophysics
and Space Science, 214,161
A Balloon-Borne Imaging Telescope for High-Energy Astrophysics
We describe an imaging telescope for observations of celestial sources in the
energy range between 30 keV and 1.8 MeV onboard stratospheric balloons. The
detector is a 41 cm diameter, 5 cm thick NaI(Tl) crystal coupled to 19
photomultipliers in an Anger camera configuration. It is surrounded by a plastic
scintillator 15 cm thick on the sides, 0.2 cm thick at the top and 20 cm thick
at the bottom. The imaging device is based upon a 19 x 19 element square MURA
(Modified Uniformly Redundant Array) coded mask mounted in an one-piece mask-
antimask configuration. The detector's spatial resolution is about 10 mm at 100
keV. This is the first experiment to use such a mask pattern and configuration
for astrophysical purposes. The expected 3sigma sensitivity for an on-axis
source observed for 104 s at a residual atmosphere of 3.5 cm-2 is 1.44 x 10(-5)
photons cm-2 s-1 keV-1 at 100 keV and 1.00 x 10(-6) photons cm-2 s-1 keV-1 at 1
MeV. The angular resolution is approximately 14 arcminutes over a 13-degrees
field of view. The instrument is mounted in an automatic platform with a
capability for pointing and stabilization in both azimuth and elevation axis
with 2 arcmin accuracy.
Wagner, R.F.,Brown, D.G.,Metz, C.E.: 1981, Proceedings of the Society of Photo-
Optical Instrumentation Engineers, 314,72
On the Multiplex Advantage of Coded Source Aperture Photon Imaging
Watt, M.P.,Ponman, T.J.,Bertram, D.,Eyles, C.J.,Skinner, G.K.,Willmore, A.P.:
1992, Monthly Notices of the Royal Astronomical Society, 258,738
The Morphology and Dark Matter Distribution of the Coma Cluster of Galaxies from
X-Ray Observations
The analysis of a spectral image of the Coma cluster obtained with a coded mask
telescope flown as part of the Spacelab 2 mission is presented. The main cluster
emission is elongated east-west and extends to a radius of at least 50 arcmin,
while an additional region of X-ray emission is detected approximately 50 arcmin
to the south-west of the cluster centre. The energy range of the instrument and
its imaging capabilities allow the temperature and density of the intracluster
gas to be determined as a function of radius, and thus allow the total cluster
mass profile to be determined. We find that the gas temperature profile is
consistent with an isothermal model, and derive a cluster binding mass of 4.2-
5.2 x 10(14) h50(-1) M. within 1 h50(-1) Mpc (24 arcmin) of the cluster centre,
the most accurate determination to date. We find no evidence for variation of
metallicity with radius. This result differs from that obtained for the Perseus
cluster; we suggest that the two clusters have different evolutionary histories,
and that the Coma cluster has recently undergone a merger which has disrupted
the pre-existing cluster conditions.
Weiss, H.: 1981, Ntz Archiv, 3,329
Imaging With Coded Aperture
Wild, P.: 1988, Electronics Letters, 24,845
Infinite Families of Perfect Binary Arrays
Wild, W.J.: 1983, Optics Letters, 8,247
Dilute Uniformly Redundant Sequences for Use in Coded-Aperture Imaging
Wild, W.J.: 1987, Sky and telescope,,126
A Gamma-Ray Pinhole Camera
Wild, W.J.,Barber, H.B.,Barrett, H.H.,Woolfenden, J.M.: 1982, Journal of the
Optical Society of America, 72,1814
Medical Coded-Aperture Imaging With a Miniature Probe
(15 or 31 element coded aperture rotated and moved axially;single NaI detector
with fibre-optic link)
Willingale, R.,Sims, M.R.,Turner, M.J.L.: 1984, Nuclear Instruments & Methods in
Physics Research Section A-Accelerators Spectrometers Detectors and Associated
Equipment, 221,60
Advanced Deconvolution Techniques for Coded Aperture Imaging
The standard deconvolution technique for coded aperture imaging is cross
correlation with the relevant mask pattern. In practice such an imaging system
is imperfect, giving incomplete coding, and direct cross correlation with the
mask introduces `ghosting' and enhanced noise fluctuations. This paper describes
the application of image processing techniques such as the Wiener Filter and
Maximum Entropy Method to deconvolve the recorded shadow pattern and illustrates
the advantage of such methods using a computer simulation of a wide field camera
for X-ray astronomy.
Willmore, A.P.,Bertram, D.,Watt, M.P.,Skinner, G.K.,Ponman, T.J.,Church, M.J.,
Herring, J.R.H.,Eyles, C.J.: 1992, Monthly Notices of the Royal Astronomical
Society, 258,621
Image Correction in a Coded Mask X-Ray Telescope
A large coded mask telescope was flown on the Spacelab 2 mission in 1985. This
was the first time that large amounts of data from such an instrument had been
obtained and much effort was devoted to optimizing the methods of reducing
detector background effects and of correcting and co-adding images. An
unexpected problem was encountered in that small errors in energy calibration
led to a large apparent detector background in the presence of bright sources.
To provide background information for the scientific results from this
instrument, and also because of their relevance to the analysis of data from
other coded mask telescopes, we describe the data processing procedures adopted.
They have led to an overall performance for the instrument which is close to
that theoretically achievable.
Willmore, A.P.,Eyles, C.J.,Skinner, G.K.,Watt, M.P.: 1992, Monthly Notices of
the Royal Astronomical Society, 254,139
Hard X-Ray-Emission from the Vela Supernova Remnant
We report the first hard (2.5-25 keV) X-ray images of the Vela supernova remnant
(SNR), resulting from observations with the University of Birmingham coded mask
telescope flown on the Spacelab 2 mission in 1985. The emission from the region
around the pulsar is resolved; the diffuse emission extends approximately 1-
degrees to the north-east and south-west, roughly aligned along the direction of
the pulsar spin axis, and produces about 48 per cent of the total emission in
the 4-25 keV band. We suggest that this region, which overlaps the peak of the
Vela-X radio source, is a synchrotron nebula. The power required to produce the
relativistic electrons in the nebula is estimated to be 75 per cent of the
rotational energy loss of the pulsar. Emission from a number of bright knots in
the shell is also detected; whilst these generally correlate with bright
features in the lower energy Einstein Observatory and the H-alpha-images, the
features at different wavelengths are not coincident, suggesting the presence of
blobs of material at a wide range of temperatures.
Willmore, A.P.,Skinner, G.K.,Eyles, C.J.,Ramsey, B.: 1981, Space Science
Reviews, 30,601
A Pseudo Random Mask Telescope for Spacelab
Willmore, A.P.,Skinner, G.K.,Eyles, C.J.,Ramsey, B.: 1984, Nuclear Instruments &
Methods in Physics Research Section A-Accelerators Spectrometers Detectors and
Associated Equipment, 221,284
A Coded Mask Telescope for the Spacelab-2 Mission
A dual coded mask telescope for the Spacelab 2 mission is now in the final
stages of preparation at Birmingham University. It is due for launch in late
1984/early 1985 and will be by far the largest and most sophisticated such
instrument to be flown in this time-frame. The design and capabilities of the
telescope will be described.
Winkler, C.,Laurance, R.J.,Tomaschek, G.: 1988, ESA Bulletin,,31
GRASP - Gamma-Ray Astronomy With Spectroscopy and Positioning
Winkler, C.,Tomaschek, G.,Bignami, G.F.,Villa, G.,Dean, A.J.,Ramsden, D.,
Durouchoux, P.,Hurley, K.,Vedrenne, G.,Lund, N.,McBreen, B.,Schonfelder, V.,
Swanenburg, B.N.: 1988, Space Science Reviews, 49,173
Mission Aspects of GRASP, ESAs Prospective Gamma-Ray Astronomy Satellite
Yamanaka, C.,Yamanaka, M.,Niki, H.,Yamada, A.,Yamamoto, Y.,Yamanaka, T.: 1984,
IEEE Transactions On Nuclear Science, 31,490
A URA Coded Aperture Camera for the Inertial Confinement Fusion Experiments
Zhang, S.N.,Fishman, G.J.,Harmon, B.A.,Paciesas, W.S.: 1994, Nature, 368,698
Earth Occultation or Coded Mask - Reply
Zirker, J.B.: 1989, Solar Physics, 120,253
Interferometric Imaging .2. Two-Dimensional Non-Redundant Arrays
Zirker, J.B.,Brown, T.M.: 1986, Journal of the Optical Society of America A-
Optics and Image Science, 3,2077
Phase Recovery With Dual Nonredundant Arrays
Zoltowski, M.D.,Silverstein, S.D.,Mathews, C.P.: 1993, IEEE Transactions On
Signal Processing, 41,2502
Beamspace Root-Music for Minimum Redundancy Linear Arrays
Beamspace Root-MUSIC is a computationally efficient beamspace implementation of
Root-MUSIC developed recently for use in conjunction with a uniformly spaced
linear array (ULA). Computationally efficient methods for employing beamspace
Root-MUSIC in conjunction with a minimum redundancy linear array (MRLA) for both
the narrow-band and wide-band cases are developed. The MRLA is attractive in
that it offers enhanced detection performance and enhanced resolution capability
relative to a ULA having the same number of elements.
These pages have been compiled by
Jean in 't Zand.
They are intended to provide
general information for those interested in coded aperture imaging.
Any citations should reference original papers as noted in the bibliography,
and requests for further information about any of the papers should be
directed to the authors thereof.
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