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Showing papers on "Speckle imaging published in 1978"


Book ChapterDOI
TL;DR: Although the aim of the research is to develop techniques useful to the engineer, developments are also being made in the use of speckle patterns for information processing, where the pattern is employed as an optical carrier.
Abstract: Publisher Summary This chapter discusses the nature of the speckle pattern and defines some of its basic characteristics. The speckle effect in optics is the generation of a random intensity pattern formed when coherent light is scattered by a rough surface or is diffused by a medium containing scattering centers. The chapter concentrates on the instrumental aspects of speckle interferometry and their applications rather than a detailed theoretical treatment. It is seen that a considerable degree of ingenuity has had to be employed to overcome the inherent difficulties that occur when interference takes place among randomly distributed phase fields rather than among smoothly varying ones. Although the aim of the research is to develop techniques useful to the engineer, developments are also being made in the use of speckle patterns for information processing, where the pattern is employed as an optical carrier.

60 citations


Journal ArticleDOI
TL;DR: Photon-counting techniques have been applied to a study of the intensity fluctuations in the image of an unresolved star at the Cassegrain focus of the 91-cm telescope of the Royal Greenwich Observatory.
Abstract: Photon-counting techniques have been applied to a study of the intensity fluctuations in the image of an unresolved star at the Cassegrain focus of the 91-cm telescope of the Royal Greenwich Observatory. Time-averaged temporal autocorrelation functions and moments of intensity have been computed. The results are discussed in terms of atmospheric turbulence and in relation to stellar speckle interferometry.

38 citations


Journal ArticleDOI
TL;DR: In this article, the effects of wavelength, spectral bandpass, and exposure time on the speckle lens-atmosphere modulation transfer function have been measured using bright stellar sources, and the effect of the exposure time has been analyzed.
Abstract: The effects of wavelength, spectral bandpass, and exposure time on the speckle lens-atmosphere modulation transfer function have been measured using bright stellar sources.

32 citations




Proceedings ArticleDOI
07 Dec 1978
TL;DR: In this paper, an image processing technique that uses interferometer data (the modulus of the Fourier transform) to reconstruct diffraction limited images is discussed, which is an iterative method that finds a real, non-negative object that agrees with the modulus data.
Abstract: For telescopes operating at optical wavelengths, the turbulence of the atmosphere limits the resolution of space objects to about one second of arc, although the diffraction limit of the largest telescopes is many times as fine. We discuss an image processing technique that uses interferometer data (the modulus of the Fourier transform) to reconstruct diffraction limited images. Data from a stellar speckle interferometer or from an amplitude interferometer can be used. The processing technique is an iterative method that finds a real, non-negative object that agrees with the Fourier modulus data. For complicated two-dimensional objects, the solutions found by this technique are surprisingly unique. New results are shown for simulated speckle interferometer data having realistic noise present.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

24 citations


Journal ArticleDOI
TL;DR: In this paper, a sequence of plots of correlation versus spatial frequency in the image for 0.25, 0.5, 1.9, and 4.7 arc sec separation binary stars with different angular separations were obtained from optically produced spatial power spectra of short-exposure images.
Abstract: Measurements of isoplanatism for speckle interferometry and speckle imaging applications have been made at a 1.57 meter aperture telescope in Hawaii. The measurements were obtained from optically produced spatial power spectra of short-exposure images showing pairs of stars with different angular separations. The result of this process is a sequence of plots of correlation versus spatial frequency in the image for 0.25, 0.5, 1.9, and 4.7 arc sec separation binary stars. Substantial correlation is found to at least 0.6 of the diffraction limit cutoff for the 4.7 arc sec pair.

22 citations


Journal ArticleDOI
TL;DR: The epochs of 372 speckle observations obtained with the 4m Mayall telescope at KPNO during 1975-77 are given for 156 unresolved visual, astrometric, spectrum, occultation, and spectroscopic binary stars as discussed by the authors.
Abstract: The epochs of 372 speckle observations obtained with the 4-m Mayall telescope at KPNO during 1975-77 are given for 156 unresolved visual, astrometric, spectrum, occultation, and spectroscopic binary stars. Specified thresholds are set for detectible angular separations and magnitude differences so that the negative observations presented here can be used to place constraints on orbital parameters.

21 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental method was developed which permits estimation of this parameter in the presence of inherently large photon and detector noises as well as unequal double-star component brightnesses.
Abstract: The parameter characterizing nonisoplanatic effects in speckle interferometry can be measured by observing double stars. An experimental method is developed which permits estimation of this parameter in the presence of inherently large photon and detector noises as well as unequal double-star component brightnesses. Data are presented on five double stars ranging from 0.22 to 3.48 arc sec in separation. The results are compared to theory and the implications to both speckle interferometry and compensated imaging are discussed.

20 citations



Journal ArticleDOI
TL;DR: In this article, it was shown that the difference between the average autocorrelation of instantaneous speckle patterns and the average cross correlation of such patterns is proportional to the autocorerelation of the image effectively uninfluenced by a turbulent atmosphere.
Abstract: It is shown that the difference between the average autocorrelation of instantaneous speckle patterns and the average cross correlation of such patterns is proportional to the autocorrelation of the image effectively uninfluenced by a turbulent atmosphere. This result leads to a useful method for the reduction of astronomical speckle data.


Journal ArticleDOI
TL;DR: Theoretical transfer functions for astronomical speckle interferometry, through a defocused telescope, have been computed assuming a log-normal complex amplitude for the incoming wavefront as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, a method for the calibration of power spectra of nonstellar astronomical objects, by the use of changes in seeing conditions during speckle-interferometric measurements, is described.
Abstract: A method is described for the calibration of power spectra of nonstellar astronomical objects, by the use of changes in seeing conditions during speckle-interferometric measurements. Results are given for an application of this technique to solar granulation. The correction of 40 analyses, determined with Fried’s parameter r0 ranging between 2.5 and 11.5 cm, provides satisfactory convergence, and thus permits estimation of the solar granulation power spectrum for frequencies up to 2.5 arc sec−1.

Journal ArticleDOI
TL;DR: In this article, it was shown how it should be possible to image star clusters, whose apparent angular extension is less than the seeing disc, by combining Labeyrie's original speckle interferometry and the extension of it due to Lynds, Worden and Harvey together with Patterson analysis as developed by X-ray crystallographers.

Journal ArticleDOI
TL;DR: In this article, a value of the wave correlation scale r0 can be obtained from the short-exposure lens-atmosphere MTF using Korff's calculations, and also show how the power spectra can be corrected so that r0 values can be extracted from resolvable object data.
Abstract: Stellar speckle interferometry of unresolved objects yields the short-exposure lens–atmosphere MTF. Using Korff’s calculations, a value of the wave correlation scale r0 can be obtained from the MTF. We demonstrate this, and also show how the power spectra can be corrected so that r0 values can be extracted from resolvable object data. Assuming the validity of Korff’s calculations for speckle interferometry, unresolved and resolved object data can be then used to test calculations for short-and long-exposure imaging. Tests with field data show only a weak distinction in speckle interferometry between short- and long-exposure imaging. A Gaussian image shape does not agree with the data.

Journal ArticleDOI
TL;DR: In this article, the amplitude and phase of the mechanical signal are obtained with a high sensitivity using synchronous detection, which is applied for studying vibrations of a piezoelectrically driven Mason horn.

Journal ArticleDOI
TL;DR: In this paper, the Fourier filtering of the double-exposed speckle pattern with small magnification change was studied and it was shown that contour fringes of equivalent in-plane displacement along the direction of filtering are obtained and that the fringe density is linearly proportional to the magnification change incurred.
Abstract: When double-exposure speckle photography is used for stress analysis of solids, displacement along the line of sight arises naturally as a consequence of specimen deformation such as Poisson’s effect, etc. This displacement causes magnification change of the speckle pattern recorded. In the this paper a model is proposed to analyze this effect. It is shown that, upon Fourier filtering of the double-exposed speckle pattern with small magnification change, contour fringes of equivalent in-plane displacement along the direction of filtering are obtained and that the fringe density is linearly proportional to the magnification change incurred. The phenomenon is quite analogous to the moire fringes created when identical gratings are superimposed with a gap between them.


Journal ArticleDOI
TL;DR: In this paper, the authors studied the error in measuring displacements of an object by speckle interferometry and showed that cameras with focal plane shutters displace to some extent, regardless of ways of mounting.

Proceedings ArticleDOI
07 Dec 1978
TL;DR: In this paper, a non-linear integral equation is solved using principle value decomposition to restore speckle images in the presence of atmospheric turbulence, and the restoration algorithm is discussed and its performance is illustrated.
Abstract: Obtaining diffraction limited images in the presence of atmospheric turbulence is a topic of current interest. Two types of approaches have evolved: real-time correction and speckle imaging. Using an "optimal" filtering approach, we have developed a speckle imaging reconstruction method. This method is based on a non-linear integral equation which is solved using principle value decomposition. The method has been implemented on a CDC 7600 for study. The restoration algorithm is discussed and it's performance is illustrated.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Proceedings ArticleDOI
18 Apr 1978
TL;DR: The use of birefringent systems permits the recording, in a single exposure, of several different granularity figures as discussed by the authors, which can be used to obtain, in the focal plane of the recording plate of A and B exactly superposed, the profile of the interference fringes which would be given in fact by three exposures, made by alternating the images (A, B, A, A), with the respective exposure times 1/2, 1, 1.1/2.
Abstract: The use of birefringent systems permits the recording, in a single exposure, of several different granularity figures. In two exposures, one with the image A, the other with the image B, we can obtain, in the focal plane of the recording plate of A and B exactly superposed, the profile of the interference fringes which would be given in fact by three exposures, made by alternating the images (A, B, A), with the respective exposure times 1/2, 1, 1/2. The signal/noise ratio is thus ten times greater than that which is given in the case of two poses in the absence of birefringent crystal.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

ReportDOI
01 Mar 1978
TL;DR: In this article, a detailed analysis of turbulence effects in speckle interferometry, i.e., the Labeyrie technique, and the Knox-Thompson algorithm, is presented.
Abstract: : A detailed analysis of turbulence effects in speckle interferometry, i.e., the Labeyrie technique, and in speckle imagery, the Knox-Thompson algorithm, is presented. Particular concern is devoted to the problem of isoplanatism, as originally we had thought that the Knox-Thompson algorithm might have a very large isoplanatic field-of-view. Our analytic results show that the isoplanatic patch size is approximately the same for Knox-Thompson and Labeyrie methods, and nearly the same as for adaptive optics. It is noted that, unlike the adaptive optics systems for which the ability to record high spatial frequency details is lost due to anisoplanatism, for the speckle methods anisoplanatism does not suppress the high spatial frequency details of the image - it merely jumbles them so that no real information is developed. From these results, it appears that a direct application of speckle techniques will not provide a significant relief from the anisoplanatism problems of adaptive optics. As part of the analysis of the Knox-Thompson method, we develop the conditions for the allowable spatial frequency separation (something done previously only by simulation). We find that the allowable spatial frequency separation should be less than 0.427 r sub 0/lambda, and preferably should be less than 0.2 r sub 0/lambda.





Journal ArticleDOI
TL;DR: In this paper, the use of instant Polaroid film has been used to perform double-exposure speckle interferometry with conventional photographic materials, permitting rapid non-destructive tests with a very simple set-up.