bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging Spectrograph for the Hubble Space Telescope
Authors: Bottema Murk
Published: February 2023

The Space Telescope Imaging Spectrograph (STIS) has been selected by NASA as a second-generation instrument for the Hubble Space Telescope (HST). Its main advantage over the first-generation spectrographs, i.e., the Faint-Object Spectrograph (FOS) and the Goddard High-Resolution Spectrograph (GHRS), lies in the use of area detectors. Two of these are 51.2 mm × 51.2 mm, 2048 × 2048 pixel Multiple-Anode Microchannel Arrays (MAMA), covering the wavelength ranges 105 nm - 170 nm (Band I, CsI photocathode) and 170 nm - 300 nm (Band II, CsTe photocathode). The other two are 55.3 mm × 55.3 mm, 2048 × 2048 pixel CCDs for the wavelength ranges 300 nm - 600 nm (Band III) and 550 nm - 1100 nm (Band IV). Each detector serves five or six different modes of operation, including low and medium-resolution first-orderspectral imaging (R = 1000 and R = 14,000), medium and high-resolution echelle modes (R = 15,000 and R = 120,000) and also a 50 arcsec × 50 arcsec camera. The optical system consists of a collimator, a grating/mirror wheel and separate refocussing optics for each individual mode. The collimator is an off-axis elliptical toroid, preceded by a 25-position slit selector.
Cross-Dispersed IR Spectrometer for Atmospheric Sounding
Authors: Pagano Robert J. , Vaughan Arthur H.
Published: February 2023

Accurate knowledge of the Earth's vertical atmospheric temperature structure is fundamental to numerical weather prediction. The National Weather Services (NWS) have stated an ultimate goal for temperature measurement of 1 degree accuracy and 1 km vertical resolution throughout the troposphere. To approach this goal next generation temperature sounders must have increased spectral coverage and increased spectral resolution. Extensive simulations indicate that a temperature sounder with spectral resolving power (λ/Δλ) of 1200 and wavelength coverage from 3.4 - 17.0 µm will significantly improve the rms temperature retrieval accuracy.
Overview of JPL Study of Optical Imaging Interferometry in Space
Authors: Synnott S. P.
Published: February 2023

JPL is currently engaged in a study for NASA of possible post-HST high resolution imaging systems in space. A near term goal of the study is to develop a technology development plan for NASA Headquarters, the implementation of which could help enable future interferometric space missions.
On the Threshold: Astrometric Optical Interferometry in Space with POINTS
Authors: Reasenberg Robert D.
Published: February 2023

POINTS (Precision Optical INTerferometry in Space) would measure the angular separation of two stars, separated by about 90 deg on the sky, with a nominal measurement error of 5 microarcseconds (μas). See Figure 1 for an artist’s rendition of the instrument mounted on the NASA MMS. A discussion of some astrophysical applications of POINTS is given by Reasenberg et al. (1988) and in less detail by Reasenberg (1984). For a pair of mag 10 stars, an observation would require about 10 minutes; the instrument would measure daily the separation of two stars for each of about 60 pairs of stars. A random sequence of such measurements, if suitably redundant, contains the closure information necessary to detect and correct time-dependent measurement biases to well below the nominal measurement accuracy. The 90 deg target separation permits absolute parallax to be determined, obviating the need for adjacent zero-parallax objects and making possible parallax measurements in all directions.
POINTS: A Stringent Test of General Relativity
Authors: Chandler J.F. , Babcock R.W. , Reasenberg R.D.
Published: February 2023

We present the results of several numerically simulated missions of an orbiting astrometric dual optical interferometer (Reasenberg, in this Digest). The second-order relativistic light deflection, that is, the part associated with terms in the metric proportional to the second power of the solar potential, has been shown to be about 10 microarcseconds (μas) for a Sun-grazing ray (Epstein and Shapiro [1980], Fischbach and Freeman [1980], Richter and Matzner [1982]). Thus, the 5-μas nominal measurement accuracy of POINTS would bring us to the threshold of a new kind of test of general relativity.
Full Aperture Metrology for High Precision Astrometry
Authors: Babcock R. W. , Marshall H.W. , Reasenberg R.D. , Reasenberg S.
Published: February 2023

POINTS (Precision Optical INTerferometry in Space) is a proposed dual astrometric interferometer with a nominal measurement accuracy of 5 microarcseconds for pairs of stars approximately 90 degrees apart. Each interferometer measures the arc-second-scale offset of its optical axis from a target star, and a metrology system, described by Phillips and Reasenberg (in this Digest), measures the approximately 90 degree angle between the two interferometers. To achieve the nominal accuracy will require monitoring the positions of the critical optical elements to a few picometer (pm). Even with the most stable materials and active temperature control, the larger optical elements, especially the 25 cm primaries, will experience thermal distortions much larger than this limit. In one subsystem, required in both interferometers, a novel technique called full aperture metrology is used to measure the appropriate average optical path length and correct for any changes. Laser light is injected into the interferometer at the primary beamsplitter and follows the starlight paths, but in the reverse direction, illuminating the active area of each optical element back to the primary mirrors. Most of the metrology light is sent out toward the target stars, but shallow phase-contrast zone plates on the primaries focus a few percent of the metrology light to axial points near the specular foci of the mirrors. The two metrology beams are collimated by athermal lenses and interfere at an auxiliary beamsplitter. The phase of the interference measures the path length difference between the two arms of the interferometer and is used to drive a null servo.
Instrumentation for Ultraviolet Spectroscopy of the Extended Solar Corona
Authors: Kohl John L.
Published: February 2023

Instrumentation and plasma diagnostic techniques are being developed to obtain a detailed empirical description of solar wind acceleration regions at heights between the coronal base and about 10 solar radii from sun center (R⊙). The goal of this work is to determine a sufficient number of observational parameters to constrain, significantly, theories of solar wind acceleration, coronal heating and solar wind composition. Although a substantial amount of data on the electron density structure of the corona already exists, there are only isolated measurements of other critical plasma parameters, except for observations of regions near the base of the corona. Ultraviolet spectroscopy provides a capability to expand greatly the number of plasma parameters that can be specified by means of remote sensing techniques. Ultraviolet measurements of spectral line profiles determine the random velocity distributions and effective temperature of protons, minor ions and electrons. Ion densities, and chemical abundances are derivable from the collisional component of the observed resonant line intensities. Outflow velocities can be determined from Doppler shifts and Doppler dimming of spectral lines. The instruments which are being developed for remote sensing of the extended corona, consist of an occulted telescope system and a high resolution spectrometer. The basic design was proven on three sounding rocket flights. Initial data on proton temperatures, and solar wind outflow velocities for heliospheric heights between 1.5 and 3.5 solar radii from sun center have been obtained. More powerful instruments are being developed for Spartan (a shuttle deployed subsatellite) and for the SOHO Mission.
Optics for Lyman, The Far Ultraviolet Spectroscopic Explorer
Authors: Cash Webster
Published: February 2023

Lyman, the Far Ultraviolet Explorer, is a space astrophysics mission designed to explore the spectra of celestial sources in the ultraviolet from 100 to 1250Å, the gap between the Hubble Space Telescope and the Advanced X-ray Astrophysics Facility. Lyman was recently selected by NASA as one of four missions to enter Phase A studies with a goal of launch in the mid-1990’s. It is envisioned as a community observatory in the tradition of the International Ultraviolet Explorer.
A High Efficiency Coronagraph for Astronomical Applications
Authors: Ftaclas Christ , Siebert Edward T. , Terrile Richard J.
Published: February 2023

Direct detection of extra-solar planetary systems is one of a class of astronomical problems requiring a significant reduction of diffracted light within a few arcseconds of a bright point source. Traditional approaches to diffraction reduction control have included pupil plane apodization, which extracts enormous penalties in effective collecting area to obtain small angle performance, and coronagraphs, in which high efficiency requires extensive occultation of the central source giving up a valuable portion of the field of view. We have developed a hybrid, high efficiency, coronagraph which is optimized for diffraction reduction within a few Airy radii of a bright unresolved source. The coronagraph utilizes a graded, or apodized transmission mask to occult the central source. Theoretical models have shown that the mask renders the Lyot stop more efficient while allowing some transmission very close to the parent star. For targets near the parent star we have found that the coronagraphic efficiency remains virtually independent of radius even when transmission losses through the mask are taken into account. Instead of being used to reduce the wings of a focal plane diffraction pattern, apodization is used in this design to reduce the diffraction wings of the pupil plane image. With a more compact pupil plane image, the application of a Lyot stop becomes much more efficient resulting in greatly improved performance without the loss of a valuable portion of the field of view. Theoretical results will be presented as well as data from a breadboard experiment.
Optics for the Extreme Ultraviolet Explorer Satellite
Authors: Finley David S. , Bowyer Stuart , Malina Roger F.
Published: February 2023

The mission of the Extreme Ultraviolet Explorer (EUVE) will be to perform an all-sky survey and produce a map of the sky in different EUV wavelength bands in the range of 70 to 900 A. Subsequent to the survey phase, pointed observations will be used for spectroscopic investigations of selected objects. The complement of scientific instruments consists of four telescopes, which are being produced by the University of California, Berkeley. The telescope optics use Wolter-Schwarzschild grazing incidence mirrors in order to achieve high throughput in the EUV, as well as good off-axis imaging.
The X-ray Large Array: A Large Scale X-ray Detector for the Space Station
Authors: Hertz Paul , Wood Kent S. , Michelson Peter F.
Published: February 2023

The Naval Research Laboratory, Stanford University, and The University of Washington have proposed a large (100 square meters) array of X-ray detectors, the X-ray Large Array (XLA), to be built at the NASA Space Station and used there for X-ray astrophysics observations. A Pre-Phase A engineering study of XLA has been completed by NASA Marshall Space Flight Center.
Calibration of the Hubble Space Telescope Faint Object Camera
Authors: Greenfield P. , Giaretta D. , Heaps C.
Published: February 2023

We will briefly describe the Hubble Space Telescope Faint Object Camera (FOC) and its operation, and the problems and solutions in calibrating it. The FOC is a photon counting imaging system with two different detectors in two different optical relays capable of f/96, f/288, or f/48 mode imaging, the last mode having a long slit spectrograph capability also (Ref. 1). The detectors (shown schematically in Figure 1), by and large the source of calibration difficulties, detect and store photons by using a three stage image intensifier with bialkalii photocathodes coupled with a television tube followed by signal processing electronics to recognize photon events. As photon events are recognized, they are stored in a digital memory which accumulates the image. The detector is capable of imaging sections of the focal plane photocathode in a wide variety of sizes and offsets (referred to as video formats). The largest has dimensions of 512 by 1024 pixels and covers a 44” by 44” area of the sky (f/48 relay).
Optical Components For Infrared And Submillimeter Wave Cryogenic Remote Sensors
Authors: Heaney J.B. , Stewart K.P. , Boucarut R.A. , Alley P.W. , Korb A.R.
Published: February 2023

The spectroscopic instruments that will go into space aboard the Cosmic Background Explorer (COBE) satellite cover the electromagnetic spectrum from 1μm to about 10cm in wavelength. Two of the instruments - the Far Infrared Absolute Spectrometer (FIRAS) and the Diffuse Infrared Background Experiment (DIRBE) - will operate at temperatures below 10K. The combined challenges of broad wavelength coverage and low temperature operation drove component design across several technology frontiers in both spectral and temperature regimes. This report will discuss the design and test of the filters, polarizers and dichroic beamsplitters that have been selected to satisfy the cryogenic sensor performance requirements in response to the broad wavelength and temperature demands.
Proposed Wavemeter for Spaceborne Laser Tuning Applications
Authors: Goad Joseph H.
Published: February 2023

A wavemeter is being developed to measure the wavelength centroids of two tunable Alexandrite lasers. These lasers are tuned on-line and off-line in a DIAL experiment to measure the vertical profiles of atmospheric water vapor and aerosols. The LASE (NASA-Lidar Atmospheric Sensing Experiment) instrument will be operated in a down-looking mode from a NASA ER-2 aircraft.
First-Order Optical Design Considerations for Spaced-Based Array Telescopes
Authors: Hochberg Eric B. , Page Norman A.
Published: February 2023

For the purpose of comparing the various optical design approaches for a space-based array telescope, the following performance goals will be used: The UV operational goal is motivated by the desire to obtain information inaccessible to the ground based astronomer while the 30 meter baseline obtains from the desire for milliarc-second class angular resolution;
Findings of Hubble Independent Optical Review Panel
Authors: Moore Duncan
Published: February 2023

Summary not available
On Orbit Performance of the HST Optical Control System
Authors: Basedow R. , Crout R. , Ftaclas C. , Nonnenmacher A.
Published: February 2023

The function of the Optical Control System (OCS) was to align the Optical Telescope Assembly (OTA) to achieve a λ/20 on-axis wavefront Its existence was dictated by the error budgets for aligning the Secondary Mirror (SM) to the Primary (PM) on the ground and for stability of the PM figure, and by the need to accomodate moisture desorption of the Metering Truss Assembly (MTA). The alignment system needed to accomodate the large OPD error which could, under worst case conditions, have been present immediately after launch, while also achieving measurement accuracies of λ/80 in the aligned state. This was to be accomplished by using a Fine Guidance Sensor (FGS) for coarse alignment, and an interferometric Wavefront Sensor (WFS) for fine alignment, both working in conjunction with the Actuator Control System (ACS). Since the final OTA wavefront error requirement was with reference to a perfect surface, an absolute reference was needed on-orbit, or equivalently, the system had to be calibrated on the ground, and thereafter had to remain stable for the life of the mission. To the extent that can be determined from a variety of on-orbit measurements, the OCS hardware and software is capable of these exacting requirements. However, the OCS does not measure to the accuracy required, apparently because spherical aberration in the PM has rendered the coma component of the ground calibration invalid.
A combined approach to HST wave-front distortion analysis
Authors: Claude  , Roddier François
Published: February 2023

Stellar images taken by the Hubble Space Telescope (HST) at various focus positions have been analysed to estimate the wave-front distortion. Rather than using a single algorithm, we found that better results were obtained by combining the advantages of different algorithms, which also permitted us to avoid some of their pitfalls. Each algorithm was thoroughly tested on computer simulations and its performance was evaluated. Gershberg-Saxton iterations were used to recover the pupil geometry appropriate to each image. Error minimization algorithms were found to be more efficient to recover low-order Zemike aberration terms and were used to estimate defocus and spherical aberration. Phase retrieval techniques including a modification of the Misell algorithm were used to refine our wave-front error estimate. These algorithms are described in details in a JPL contract report [1], We summarize here the results obtained so far.
Reflective Correctors for the HST Axial Instruments
Authors: Bottema Murk
Published: February 2023

Soon after it was established that the spherical aberration in the HST was due to excessive asphericity of the primary mirror, a group of astronomers and optical experts was formed (the HST Strategy Panel*) to investigate possible means of correction. After reviewing some twenty-five different ideas, the Strategy Panel recommended individual reflective correctors for three of the axial scientific instruments (ASI), namely, the Faint Object Camera (FOC), the Faint Object Spectrograph (FOS), and the Goddard High Resolution Spectrograph (GHRS), be installed during the first scheduled refurbishment mission. The fourth ASI, the High Speed Photometer (HSP), was to be replaced by a new module, the Corrector Optics Space Telescope Axial Replacement (COSTAR), to form a basis for deployment of the corrector systems. Replacement in the same mission of the fifth instrument, the Wide Field and Planetary Camera (WF/PC) by a new version was already planned by NASA. Its optics are modified to compensate the spherical aberration internally.
Science Recovery with the HST WFPC-2 Camera System
Authors: Trauger John
Published: February 2023

The second Wide Field and Planetary Camera (WFPC-2) was already in development when the large surface figure error was discovered in the HST primary mirror. The WFPC-2 was envisioned as a backup for the original WFPC launched aboard the HST, designed for on-orbit replacement of the WFPC during a Shuttle servicing mission. WFPC-2 incorporates evolutionary improvements in the CCD sensor technology, the complement of 48 photometric filters, and sensitivity at far-ultraviolet wavelengths. A servicing mission now scheduled for late 1993 will be our first opportunity to correct the HST aberrations through modified science instruments and to commence science programs which require high quality imaging. The success of this servicing mission in the eyes of the science community will require imaging capabilities close to those originally promised for HST.
Evaluation of a silicon carbide telescope mirror for the vacuum ultraviolet
Authors: Leviton Douglas B. , Saha Timo T. , Wright Geraldine A. , Keski-Kuha Ritva , Boucarut Rene A.
Published: February 2023

Evaluations of the SiC demonstration telescope mirror for the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument for the Solar and Heliospheric Observatory (SOHO) mission have been carried out at the Diffraction Grating Evaluation Facility (DGEF)1 at Goddard Space Flight Center. These evaluations include: image quality at 124 nm; scatter into off-specular angles at 124 nm; visible image quality; figure assessment using a ZYGO Mark IV interferometer; microroughness evaluation of the surface using a WYKO optical interference heterodyne profilometer; and scatter photographs of the mirror surface illuminated with a collimated beam at off-specular angles. An analytical model of the vacuum ultraviolet experiments has been developed2 to predict the experimental outcomes. Experiments are described and results are compared to analytical predictions based on the surface metrologic data gathered.
On-Orbit Performance of the HST Fine Guidance Sensors
Authors: Eaton David J. , Whittlesey Richard , Allen Bruce , Stoll Roy , Abramowicz-Reed Linda , Basedow Robert , Margulies Marcel
Published: February 2023

The three Fine Guidance Sensors (FGS's) of the Hubble Space Telescope (HST) have two principal functions: 1) providing an absolute pointing reference to the telescope pointing control system, and 2) serving as an astrometry instrument.
Ultra-Violet Calibration Sources for the Hubble Space Telescope Wide Field Planetary Camera II
Authors: Majorana L. N. , Morrow W. H.
Published: February 2023

The recent difficulties with GOES satellites underline the importance of reliable calibration sources for space use. Even though the calibration component is a small fraction of the budget of any space qualified instrument, it's failure can result in a catastrophic loss of data.
Technique for vacuum ultraviolet image dissection
Authors: Leviton Douglas B.
Published: February 2023

Image evaluation for optical components in the vacuum ultraviolet (VUV) having subarcsecond resolution has been developed at the Goddard Space Flight Center's Diffraction Grating Evaluation Facility (DGEF)1 using raster scan image dissection. A microscopic, rectangular aperture2 is discretely positioned along scan lines throughout an image area and the light passing through it is detected to build up an image irradiance map. The technique simulates a "one pixel at a time," VUV-sensitive, photon counting, area array detector with high dynamic range and pixel sizes down to below 2 um. Image statistics provide encircled energy and angular resolution profiles for imaging systems in the VUV. Comparisons of raytrace data and experimentally obtained images are presented.
NASA's Future Plans for Space Astronomy and Astrophysics
Authors: Kaplan Mike
Published: February 2023

This paper presents NASA's plans for future space astronomy and astrophysics through the first decade of the next century. We will discuss specific missions and mission concepts, as well as plans to develop optics and sensors technology to enable these missions.
Cryogenic Optical Testing of a Fused Quartz Mirror
Authors: Melugin Ramsey K. , Augason Gordon C. , Howard Steven D. , Young Jeffrey A.
Published: February 2023

The Space Infrared Telescope Facility (SIRTF) is an orbital, great observatory planned by NASA to enable diffraction-limited astronomical studies in the infrared from 2 μm to 700 μm. The telescope must be cryogenically cooled by Superfluid Helium at 2.5 K to provide the extreme sensitivity required for natural-background-limited observations. Concern about the image quality of the telescope operating at the extremely low temperature led to a cryogenic optics technology program.
Absolute phasing of segmented mirrors using the Polarization Phase Sensor
Authors: Klumpe Herbert W. , Lajza-Rooks Barbara , Blum James
Published: February 2023

To achieve optimum performance with segmented mirror systems, the individual mirror segments must be aligned with respect to each other. This alignment is often referred to as phasing, and two mirror segments which have met this condition are termed in-phase. Mirror phasing requires that accurate tip, tilt, and piston measurements be made. The Polarization Phase Sensor (PPS) demonstrates a novel approach to mirror segment alignment.
Predicted X-Ray Performance of the AXAF Outer Mirror Pair
Authors: Van Speybroeck Leon P.
Published: February 2023

The recently polished outer AXAF mirror pair soon will be tested at Marshall Space Flight Center's new x-ray facility. The expected performance is discussed.
Effects of Ion Beam Deposition on the Optical Scattering of Metal Coatings
Authors: Raouf Nasrat A. , Al-Jumaily Ghanim A. , Coulter Daniel R.
Published: February 2023

Reduction of optical scattering is becoming a concern in the space and astronomical applications. Substrate surface roughness, substrate bulk material and the film coating microroughness contribute to the scattering. In the case of metallic coated substrates: only the substrate surface roughness and the coating roughness will contribute to the increase of optical scattering. In this paper we examine the effects of ion beam processes on the optical scattering and surface microroughness of super polished substrates coated with metallic Platinum.
PEARLSS, A Sensor System Simulation of the Effects of Contaminants
Authors: Whitlock L. A. , Jackson J.L.
Published: February 2023

Space-borne optical systems have become increasingly important in recent history. Contamination of such sensors in space is a critical issue because it degrades the capability to detect or identify objects of interest through stray light scatter into the field-of-view (FOV), signal attenuation, false targeting, defocussing of the target image, etc. The magnitude and structure of the noise contribution from contamination must be weighed against the magnitude and structure of other noise components in order to determine its importance. Clearly, the problem is system design dependent and a flexible means of simulation is required to address the issue. Many previous models have dealt only with pieces of the problem; PEARLSS (Particulate Effects Analysis on Response Levels of Space-borne Sensors) is a model which deals with contamination generation, migration, deposition, and resulting optical degradation in a single 'end-to-end' code.
Polishing Mechanism of Fused Silica Glass
Authors: Izumitani Tetsuro , Adachi Shoji
Published: February 2023

We showed the polishing mechanism of optical glass. It is that the hydrated layer formed by the chemical reaction between glass and polishing slurry is scratched and removed by the polishing grains, so the polishing rate is determined by the formation rate and the hardness of the hydrated layer and is dependent upon the chemical durability and the hardness of glass, therefore, it can be said that polishing of glass is a kind of chemico-mechanical process.
Comparison of Polishing with Cerium Oxide and Diamond
Authors: Parks R. E. , Thurston Timothy , Attwood Deborah , Kreischer Cody B.
Published: February 2023

A series of 3cm diameter, BK-7 glass samples were ground down through a series of loose abrasives ending with 12µ aluminum oxide. Half of the samples were then polished using "Liquid 85" cerium oxide compound and pitch for various times. The balance of the samples were polished with 10µ diamond in an epoxy dot matrix and water containing 5% water soluble oil coolant. Identical pressures (about 0.3psi) and velocities (about eight inches per second) were used in both cases. This paper compares the polish obtained, the speed of polish and the apparent residual surface damage as exposed by hydrofluoric acid etching.
Electric Field-Assisted Fine Finishing Using Electrophoresis Phenomenon
Authors: Kurobe Toshiji , Imanaka Osamu
Published: February 2023

Novel finishing method has been exceedingly required in the fields of electronics and precision machinary associated with the progress of technology. A variety of polishing methods [1,2,3] have been hitherto developed in such fields. A newly-developed polishing method is devised on the basis of the electrophoresis phenomenon of a grain in the liquid, which is able to move in the electric field. This polishing method is named " Field-assisted Fine Finishing ". It is found from the theoretical analysis that the moving mode of a grain has been influenced by the dielectric constant and the viscosity of the liquid, δ-potential and the supplied potential. It has been found from experiments that the new polishing method has possibilities of flexible surface finishing and the stock removal rate by varying the current or potential to the electrode.
Damage Susceptibility of Ring Laser Gyro Class Optics
Authors: Stowell W. Kent
Published: February 2023

The surface quality of optics used in an extremely sensitive laser instrument, such as a Ring Laser Gyro (RLG), is critical. Experimental evidence is presented on the damage to this class of optics that results from the typical processing and handling. Also presented is a possible solution to this problem.
Geometric Deconvolution of Artifacts in Limited View Computed Tomography
Authors: Rangayyan Rangaraj M. , Gordon Richard
Published: February 2023

Images reconstructed using a limited number of projections measured over a narrow angle range are characterized by elliptic distortions along the directions of the raws used, and poor contrast at angles not used (anisotropic resolution). Thus, for example, a reconstruction computed using a few views measured about the vertical would have a vertical ellipsoidal distortion and poor resolution along the horizontal. We are interested in this particular case in connection with our experiments to achieve computed tomography from a few radiographs acquired at different angles using an ordinary overhead or mammographic x-ray unit. The aim is to transmit these images over telephone lines to provide inexpensive computed tomography to people living in remote areas. The angular coverage is restricted to the range 55-125 degrees. We are also attempting to compute high resolution tomographic images of the breast from a few film mammograms. Similar cases arise in industrial non-destructive testing and electron microscopy of biological macromolecules.
Tomographic Imaging with Limited View Angle Using an Expansion on A Set of Eigenfunctions Adapted to Space-Limited Objects
Authors: Garnero Line , Brunol Jean
Published: February 2023

In many radiation imaging applications, such as X-ray computerized tomography or nuclear medicine, tomographic systems have been recently developped, which image an object from an angulary restricted number of projections. It is well known that in such a case, some Fourier components are missing {1}, and thus analytical reconstructions, such as Fourier synthesis can no longer be used. But, the algebraic methods allow to take advantage of "a priori" informations on the object, in order to recover the missing data. Many authors have proposed different reconstruction techniques, that combine limited projection data with a priori object information through iterative revisions in both image and transform spaces {2-3}. These methods in general consume much computer time.
Linear Estimation with a Size Constraint
Authors: Lahart M. J.
Published: February 2023

Least squares estimation has been used in image processing since Helstrom showed several years ago that Wiener filters could be used to deblur images1. In its most usual application, the technique uses the image data and the object and noise autocorrelation functions to compute the object that corresponds to the minimum of the sum of the squares of the noise values. We show here how least squares techniques can also be used to estimate spectral components when the size and shape of an object are known. Examples of missing components are high frequency Fourier components of an object that has been subjected to low pass filtering (blurring) and transforms of missing projections of an object that is to be restored through computed tomography.
The Phase Problem in Object Reconstruction and Interferometry
Authors: Ferwerda H.A.
Published: February 2023

In this contribution I shall review phase problems from different fields of optics which can be handled with similar techniques. In all cases the problem is to reconstruct the phase of a function from its modulus. In object reconstruction we have to know the complex image wave function (w.f.) while the intensity distribution only gives its modulus. In speckle interferometry only the autocorrelation of the brightness distribution of the source (or equivalently the modulus squared of its Fourier transform) is measurable. In interference microscopy often only the visibility of the interference fringes formed in a Michelson interferometer can be observed, yielding the absolute value of the complex degree of temporal coherence. But we also need its phase for the calculation of the spectral distribution of the source.
A Sufficient Condition for Phase Retrieval in Two Dimensions
Authors: Fiddy M. A. , Brames B. J. , Dainty J. C.
Published: February 2023

Eisenstein's criterion for irreducibility is used to modify an object function, thus ensuring uniqueness of phase retrieval in two dimensions.
Dependent and Independent Constraints for a Multiple Objective Iterative Algorithm
Authors: Mait Joseph N. , Rhodes William T.
Published: February 2023

Constrained iterative algorithms have been applied primarily to single objective applications,1 where by objective we mean that distribution that is to be reconstructed from partial information or synthesized with desired characteristics. In a recent work by the authors,2 Fienup's error-reduction algorithm was extended to multiple objectives, as shown in Fig. 1, and was applied to a specific synthesis problem with two objectives. In this paper, we illustrate an important characteristic of multiple objective iterative algorithms, dependent constraints.
Singular Value Analyses of Inversion of Laplace and Optical Imaging Transforms
Authors: Bertero M , Pike E R
Published: February 2023

The use of the eigenvalues and eigenfunctions of the first order Fredholm equations describing optical imaging has long been known. The eigenvalues and eigenfunctions of the first order Fredholm equation of the Laplace transform have only recently been discovered and similarly used (McWhirter and Pike 1978). Let us consider for simplicity the one dimensional case with magnification unity. For an eigenfunction to be defined the linear mapping A:f → g of the "object" f into its "image" g must define a compact bijective operator A of, say, L2 (−1,+1) into itself.
A technique for the calculation of the global extremum of a function of several variables
Authors: Slump C.H. , Hoenders B. J.
Published: February 2023

The determination of the global extremum of a function is a notorious numerical problem when there are local extrema present. The numerical algorithm which has to determine the global extremum iteratively is in this case very likely to produce a local extremum in the neighborhood of the initial guess of the solution. Moreover, usually one cannot be sure not to have missed an extremum, i.e. various procedures together with various initial values might still overlook the global extremum.
Mathematical Results of the Phase Retrieval Problem for Bandlimited Functions of Several Variables
Authors: Lawton Wayne M.
Published: February 2023

The purpose of this paper is to answer the following questions concerning bandlimited functions F(x) and G(x) of a vector variable x = (x1,…, xN) ϵ RN.
Speckle Interferometry Image Reconstruction Techniques Proceeding from the Phase of the Fourier Transform
Authors: Bruck Yuri M. , Sodin Leonid G.
Published: February 2023

The familiar methods of image reconstruction employed in the speckle interferometry require measurements of both the transfer function modulus [1] and phase [2] with the aid of a reference point object. In case the scattering is isotropic, the phase can be measured with a better accuracy than the modulus which makes suggestive image reconstruction from the phase alone. Hayes et al. [3] and Bruck and Sodin [4] have put forward techniques for reconstructing one- and two-dimensional images from either exact [3] or approximate [4] knowledge of the phase. In this paper we suggest reconstruction algorithms for those cases where the spectrum phase is known to a limited accuracy and no data exist as to the size and position of the image. Considered are the uniqueness and accuracy of the reconstruction, and image identification.
Signal Deconvolution Using Frequency and Time Domain Magnitude Constraints
Authors: Trussell H.J. , Sura P.N.
Published: February 2023

In many signal restoration problems we have very limited knowledge about the statistics required for implementation of the most common restoration techniques, for example, Wiener filtering. We do, however, possess some practical a priori knowledge about the nature of the signal we week to estimate. Because of this a priori knowledge, it may be suboptimal to use methods which make few assumptions about the nature of the ideal signal, for example, maximum entropy restoration [1]. Iterative restoration methods can be easily modified to incorporate such a priori knowledge while requiring little statistical information [2].
A Simple Method for Superresolution
Authors: De Santis P. , Gori F. , Guattari G. , Palma C.
Published: February 2023

Since the invention of superresolving pupils by Toraldo di Francia in 1952 [1] , superresolution has attracted the attention of many authors. As it is well known, the possibility of superresolution rests on some "a priori" information about the object. In the case of superresolving pupils, the only prior information is that the object has a finite extent. Elegant as they are from the theoretical point of view, the superresolving pupils [2] seem difficult to fabricate. As a matter of fact, rather severe tolerance conditions should be met in the fabrication and, to our knowledge, no practical superresolving pupil has been produced so far.
Iterative Restoration of Images with Missing High-Frequency Components Using Adaptive Regularization
Authors: Maeda Junji , Murata Kazumi
Published: February 2023

The problem of restoring the details of bandlimited images of spatial finite extent or recovering the missing high-frequency components has recently been discussed extensively. Since the present problem is ill-conditioned, certain types of regularization techniques are required [1-5]. Moreover, some types of a priori information or constraints are used to overcome the ambiguity and instability of the solution [6-9].
Super-Resolution and Signal Recovery Using Models of Neural Networks
Authors: Farhat Nabil H. , Miyahara Sunji
Published: February 2023

Content addressable memory (CAM) based on models of neural networks [1], [2], offer capabilities that are useful in information processing, signal recovery, and pattern recognition. These include speed (stemming from their inherent parallelism and massive interconnectivity), robustness (stemming from their fault tolerant and soft-fail nature) and most significantly, relative to the subject matter of this meeting, their ability to recognize a partial input i.e., when the initializing input is an incomplete version of one of the stored entities. The latter two features are in fact synonymous with the realization of super-resolution where a function is recovered from a noisy or imperfect part. These attractive features are traceable to the highly nonlinear and iterative nature of feedback employed in such CAMs.
Phase Retrieval Algorithm Using a Convolution Based Hilbert Space
Authors: Cetin A. Enis , Ansari Rashid
Published: February 2023

A phase retrieval algorithm using the method of projection onto convex sets (POCS) [1,2] in a new Hilbert Space framework which is based on convolution is described. In this space, the set of sequences with a prescribed Fourier Transform magnitude constitute a closed convex set, which is not true in (or L2) Hilbert space. This property of the constraints ensures convergence in the POCS method. Examples of phase retrieval for 2-D sequences are presented.
Three-dimensional Optical Microscopy of Biological Specimens
Authors: Agard David A. , Hiraoka Yashushi , Sedat John W.
Published: February 2023

The ability to analyze biological specimens in three dimensions represents one of the major achievements of modern structural biology. For all but the simplest repeating structures, three-dimensional analysis is a crucial prerequisite for understanding complex biological assemblies. Near atomic resolution analysis of of crystalline proteins, nucleic acids, and viruses by X-ray crystallography approaches the routine. The current frontier focuses on the three dimensional analysis of non-crystalline, non-symmetric biological structures of cellular dimension. Electron microscope tomography and three dimensional optical microscopy are perhaps the most powerful methods for these studies.
Review of Some Inverse Methods in Electromagnetics
Authors: Mittra R. , Habashy T.M.
Published: February 2023

In this paper we present a brief review of some methods for solving the inverse problem in electromagnetics, methods that are useful for the problem of profile inversion of a layered medium whose complex refractive index varies as a function of depth or the radial distance. The scope of the paper is limited to a discussion of rigorous techniques only, and the numerical schemes based on the parameter estimation algorithms, or approximate methods, e.g., migration techniques and the ray methods, are not included.
Phase Retrieval Using Two Fourier Intensities
Authors: Kim Wooshik , Hayes Monson H.
Published: February 2023

The two-dimensional discrete phase-retrieval problem is concerned with the reconstruction of a signal, or image, x(m, n), from the magnitude (intensity) of its Fourier transform, |X(ω1,ω2)|- Phase retrieval is an important problem that arises in a variety of different applications including x-ray crystallography, astronomy, electron microscopy, optics, and signal processing [1-5]. There are three issues that need to be considered in the solution of the phase retrieval problem: the uniqueness of the solution, the development of phase retrieval algorithms that reconstruct a signal from its Fourier transform intensity and any á priori information that might be available, and the sensitivity of the reconstruction to computational noise and measurements errors. It is now well known that if a two-dimensional signal with finite support has a z-transform that is an irreducible polynomial then the signal is uniquely defined to within a trivial ambiguity by the intensity of its Fourier transform [6]. This result becomes important with the fact that it has been shown that “almost all” discrete two-dimensional signals with finite support have z-transforms that are irreducible [7]. In spite of this uniqueness of the solution, however, the reconstruction of a signal from its Fourier intensity remains a difficult problem.
Phase Retrieval for a Complex-Valued Object Using a Low-Resolution Image
Authors: Fienup J.R. , Kowalczyk A.M.
Published: February 2023

Phase retrieval from a single Fourier intensity distribution is very difficult for complex valued objects unless the object has a support that is very well known, has a special type of support, or has strong glints [1-3]. In this paper we show that even the most difficult types of complex objects can be reconstructed if one has a very low-resolution intensity image of the object to supplement the Fourier intensity data.
Two-Dimensional Phase Correction of Synthetic Aperture Radar Imagery
Authors: Ghiglia Dennis C. , Mastin Gary A.
Published: February 2023

A two-dimensional synthetic aperture radar (SAR) phase correction algorithm is described as a natural extension of a one-dimensional technique developed previously. It embodies many similarities to phase gradient speckle imaging and incorporates improvements in phase estimation. Diffraction limited performance has been obtained on actual SAR imagery regardless of scene content or phase error structure. The algorithm is computationally efficient, robust, and easily implemented on a general purpose computer or special purpose hardware.
A Filtering Approach to the Two-Dimensional Volume Conductor Forward and Inverse Problems
Authors: Xydis Thomas G. , Yagle Andrew E.
Published: February 2023

The volume conductor inverse problem is the problem of reconstructing a two-dimensional distributed voltage source from measurements of the electric field it produces at the surface of an intervening medium. The intervening medium may be homogeneous or horizontally layered, with differing conductivities in each layer. The problem is assumed to be quasistatic (a “snapshot” in time); this is reasonable for the impedances encountered in biological tissues.
Multiple Source Localization Via Redundancy Exploitation With Geometrically Redundant Planar Sensor Arrays
Authors: Stavrinides Demosthenis , Zoltowski Michael D.
Published: February 2023

A new scheme for estimating the respective radial directions of multiple radiating sources is introduced. The main contribution is the incorporation of a technique referred to as "Pseudo Forward Backward averaging" which judiciously exploits the inherent redundancy in a planar sensor array exhibiting the ESPRIT structure [2]. ESPRIT is a recently proposed bearing estimation algorithm that works with an array of M matched sensor pairs (2M sensors total) referred to as doublets, grouping one element of each doublet into an X array, and the other into a Y array. The displacement vector, denoted
d→, between the two members of a given doublet is assumed to be the same for each doublet and the two members of each doublet are required to possess identical radiation patterns. ESPRIT allows us to estimate the angle between
d→ and the unit normal to the i-th arriving wavefront, denoted by
r^
i
, i.e.,
d→⋅r^
i
. In contrast to spatial spectrum estimation algorithms such as MUSIC and Maximum Entropy which require the plotting and searching of a multi-modal, two dimensional surface, the estimates obtained via ESPRIT are simply found by solving for the generalized eigenvalues of a judiciously formed data pencil. More specifically, we shall employ a refinement of ESPRIT, referred to as PRO-ESPRIT [1], the development of which was predicated on exploiting the inherent redundancy built into the ESPRIT array structure described above.
Necessary and sufficient conditions for the existence and synthesis of bipolar incoherent pointspread functions
Authors: Mait Joseph N.
Published: February 2023

In 1978 Lohmann and Rhodes [1] presented a general two-channel hybrid system for bipolar incoherent spatial filtering. The work by Lohmann and Rhodes is significant in that it presented a unified and compact analysis of such filtering. Subsequent work by Mait [2,3] is also significant for its consideration of synthesis, or design, of such systems so as to produce a specific bipolar response.
Row and Block Action Projection Techniques for Image Restoration
Authors: Podilchuk Christine I. , Mammone Richard J.
Published: February 2023

The discrete image restoration problem consists of solving a set of linear equations where g represents the measured image, the M × N matrix H denotes the degradation operator and f represents the image to be determined. Since H is usually an ill-conditioned or rank-deficient matrix, solving the set of equations is not straightforward. In addition, the set of linear equations are inconsistent due to measurement errors, quantization noise, and inaccuracies in modeling. Therefore, direct inversion techniques are not applicable.
Statistical Methods for Image Restoration and Image Reconstruction
Authors: Chen Chin-Tu , Johnson Valen E. , Wong Wing H. , Hub Xiaoping , Metz Charles E.
Published: February 2023

This paper offers a general review of the application of statistical methods, including both maximum likelihood and Bayesian estimators, to problems in image restoration and image reconstruction.
Phase-Diverse Speckle Interferometry
Authors: Paxman Richard G. , Schulz Timothy J. , Fienup James R.
Published: February 2023

Imaging extended objects through atmospheric turbulence can be accomplished with stellar speckle interferometry, which requires the collection of many image frames of the same object. The exposure time for each frame must be short enough (≈ 10 msec) that the evolving atmosphere can be regarded as frozen during the exposure. Current stellar speckle interferometric approachs, including Labeyrie’s method, Knox-Thompson, and triple correlation, perform an averaging of the data in the process of individually estimating the Fourier modulus or the Fourier phase of the object. The final estimated object is constructed by combining the Fourier modulus and phase estimates and performing an inverse Fourier transform. In addition, a calibration procedure must be performed using images of an unresolved object through atmospheric turbulence having the same statistics.