scispace - formally typeset
Search or ask a question

Showing papers on "Speckle imaging published in 1995"


01 Jan 1995
TL;DR: In this paper, Fourier and Statistical Optics Fourier Optics statistical Optics Turbulence Effects on Imaging Systems Index of Refraction Fluctuations in the Atmosphere Statistics of Index of Reconstant Fluctuation Wave Propagation through Random Media First-Order Turbulences Effects on Incoherent Imaging Modal Expansions of Phase Perturbation Phase Screen Generation Speckle Imaging Techniques Introduction Overview of Speckles Imaging SpeckLE Interferometry Fourier Phase Estimation Techniques Image Reconstruction for Specksle Imaging Conclusion Adaptive Optical Imaging Systems Introduction Factors
Abstract: Introduction Overview of the Problem Area Historical Overview of Imaging Through Turbulence Overview of the Book Background: Fourier and Statistical Optics Fourier Optics Statistical Optics Turbulence Effects on Imaging Systems Index of Refraction Fluctuations in the Atmosphere Statistics of Index of Refraction Fluctuations Wave Propagation through Random Media First-Order Turbulence Effects on Incoherent Imaging Modal Expansions of Phase Perturbation Phase Screen Generation Speckle Imaging Techniques Introduction Overview of Speckle Imaging Speckle Interferometry Fourier Phase Estimation Techniques Image Reconstruction for Speckle Imaging Conclusion Adaptive Optical Imaging Systems Introduction Factors that Degrade AOI Systems Performance Adaptive Optical System Components and Models AOI System Performance Modeling Summary Hybrid Imaging Techniques Introduction Deconvolution from Wavefront Sensing Methods Involving Adaptive Optics Conclusion Index

96 citations


Journal ArticleDOI
TL;DR: In this article, the authors used speckle imaging to monitor 20 T Tauri binary stars with separations ranging from 0".09 to 1" (13-140 AU) and demonstrated that the majority of the observed systems show significant relative velocities which are not consistent with the motion expected for HH objects, and thus are not the result of differential proper motion, and are consistent with orbital motion.
Abstract: Over a five year period, we have used speckle imaging to monitor 20 T Tauri binary stars with separations ranging from 0".09 to 1" (13-140 AU). This project is aimed at detecting the relative motion of the component stars to ascertain whether or not the observed companions (1) are stellar in nature, as opposed to being HH objects, and (2) are gravitationally bound to the primary stars. These observations demonstrate that speckle imaging measurements of close binary stars' separations can be made with an accuracy of a few milliarcseconds. The majority of the observed systems show significant relative velocities which (1) are not consistent with the motion expected for HH objects, (2) are greater than the velocity dispersion of these star-forming regions and thus are not the result of differential proper motion, and (3) are consistent with orbital motion. This is the first demonstration that these systems are physically bound. Furthermore, these relative velocity measurements provide dynamical evidence that the average total mass of these T Tauri binary star systems is ~l.7M_⊙.

95 citations


Journal ArticleDOI
TL;DR: Speckle pattern and shearing interferometry are becoming more and more important in the areas of precision measurement and nondestructive testing as mentioned in this paper. But they are not suitable for non-destructive testing.

81 citations



Journal ArticleDOI
TL;DR: In this article, a homomorphic filter coupled with a Wiener filter is proposed to reduce the speckle in radar images, and the autocorrelation of the noise-free image is evaluated by an iterative procedure.
Abstract: The presence of speckle in radar images reduces the radiometric resolution and renders less efficient the procedures for texture class discrimination. We present an algorithm devoted to speckle reduction in syntheticaperture radar images based on a homomorphic filter coupled with a Wiener filter. To construct the Wiener filter we analytically evaluate the autocorrelation function of the noise, starting from the first two orders of statistics of the noise, before performing the homomorphic transformation (a logarithmic one, in the case of multiplicative noise), and the autocorrelation of the noise-free image is evaluated by an iterative procedure. The algorithm, tested on both simulated and actual synthetic-aperture radar images, provides very promising results and shows the usefulness of the proposed method.

58 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used phase-stepping speckle interferometry to verify that these sources coincide with points of very low or zero modulus, and that the displacement of sources as a result of specckle decorrelation between measurements of two phase maps leads to closely spaced dipole pairs of sources in the phasedifference map.
Abstract: One of the most successful phase-unwrapping algorithms uses branch cuts to join discontinuity sources that mark the beginning or the end of a 2π phase discontinuity. Here, using phase-stepping speckle interferometry, we verify that these sources coincide with points of very low or zero modulus and that the displacement of sources as a result of speckle decorrelation between measurements of two phase maps leads to closely spaced dipole pairs of sources in the phase-difference map. By measuring the movement of sources at high magnification, we find that the length distribution of correct branch cuts needed to unwrap a phase-difference map is approximately Gaussian. This provides a theoretical justification for unwrapping with the set of branch cuts that minimizes the sum of squares of cut lengths.

43 citations


Journal ArticleDOI
TL;DR: A new method has been developed to remove noise from the deformation phase map obtained by a phase-shifting electronic speckle pattern interferometry, which estimates almost noise-free phase values directly from the distributions of the intensity differences of four interference patterns by a least-squares fit.
Abstract: A new method has been developed to remove noise from the deformation phase map obtained by a phase-shifting electronic speckle pattern interferometry. Unlike usual methods, it estimates almost noise-free phase values directly from the distributions of the intensity differences of four interference patterns by a least-squares fit. The fluctuations of uniform deformation phases are reduced to less than 0.05 rad with a 5 × 5 pixel fitting window. The so-called sawtooth phase jumps that are due to the use of arctangent functions are retained sharply in this method.

41 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the wavefield intensities on the reliability of phase measurements was investigated for phase-shifting speckle interferometry using a smooth reference wave, and the first-order statistics of the background intensity and the modulation of the interference pattern were calculated and then used to determine the efficiency of the measurement, defined as the fraction of points that yield an interference signal exceeding a given modulation threshold.

34 citations


Journal ArticleDOI
TL;DR: In this paper, different arrangements for digital double-pulse holographic and speckle interferometry for vibration analysis are described, and applications of the method for measuring rotating objects are discussed, together with the derotator needed.

34 citations


Journal ArticleDOI
TL;DR: The unaided eye has an angular resolution of about 1 arcminute as mentioned in this paper, however, atmospheric turbulence limits the resolution at visible and infrared wavelengths to 1 arcsec or a little better.
Abstract: The unaided eye has an angular resolution of about 1 arcminute. From the invention of the telescope in the 17th century to the middle of the 1970s, astronomers improved on this resolution by two orders of magnitude by building bigger telescopes and putting them at good sites. Even at good sites, however, atmospheric turbulence limits the resolution at visible and infrared wavelengths to 1 arcsec or a little better. In the past 20 years, a further factor‐of‐ten improvement has come with two developments that deal with the atmosphere: “speckle interferometry,” in which the blurred image is frozen in a short exposure and the image is reconstructed from many exposures, and adaptive optics, in which the effects of the atmosphere are sensed, then corrected with a defbrmable mirror, before the image is recorded. (See Laird A. Thompson's article in PHYSICS TODAY, December 1994, page 24.)

32 citations


Proceedings ArticleDOI
14 Jun 1995
TL;DR: In this paper, the effect of speckle integration implicit in digitization by pixels of finite size is considered using computer-generated specckle patterns, and it is shown that the phase errors decrease monotonically with decreasing speckles diameter.
Abstract: Phase measurements using digital speckle pattern interferometry are subject to random errors due to speckle decorrelation and electronic noise. A phasor description of speckle decorrelation is introduced from which the r.m.s. phase error is calculated. Phase noise due to additive Gaussian errors on the phase-stepped images is shown to be statistically equivalent to that from decorrelation, allowing the r.m.s. phase error from electronic noise to be obtained analytically. The currently used noise reduction strategy of speckle averaging is shown to be optimal in that it provides the maximum likelihood estimate of speckle phase change. Finally, the effect of speckle integration implicit in digitization by pixels of finite size is considered using computer-generated speckle patterns. It is shown that the phase errors decrease monotonically with decreasing speckle diameter.

Journal ArticleDOI
TL;DR: A digital phase-mapping method has been developed for application in real-time electronic speckle interferometry studies and its principles and application to a continuously deforming object are described.
Abstract: A digital phase-mapping method has been developed for application in real-time electronic speckle interferometry studies Its principles and application to a continuously deforming object are described An efficient digital image-processing algorithm has been developed that permits quantitative interpretation of the resulting phase maps

Journal ArticleDOI
TL;DR: The results indicate that the optical quality of the eye reduces the spatial bandwidth of vision even at luminances near the foveal threshold, consistent with noise-limited behavior.
Abstract: Optical properties of the eye contribute to the reduced visibility of spatial patterns at low luminance. To study the limits of spatial vision when optical factors are minimized, we measured contrast-sensitivity functions (CSF’s) for 543.5-nm laser interference fringes imaged directly on the retina. Measurements were made in the fovea at four luminance levels, ranging from 0.3 to 300 photopic trolands (Td). At each luminance the fraction of coherent light in the stimulus pattern was varied to assess the masking effects of laser speckle, which is visible as spatial noise in fields of coherent light. Compared with published CSF’s obtained under natural viewing conditions, interferometric CSF’s were similar in height but broader, with the range of visibility being extended to higher spatial frequencies. The masking effects of speckle were greatest at the highest luminance and were negligible at the lowest luminance. For low coherent fractions, contrast sensitivity improved over the entire luminance range at a rate consistent with a square-root law; with purely coherent light, sensitivity tended to level off at approximately 30 Td because of speckle masking. The results indicate that the optical quality of the eye reduces the spatial bandwidth of vision even at luminances near the foveal threshold. The change in interference fringe visibility with luminance is consistent with noise-limited behavior, and the masking effects of speckle noise diminish as luminance decreases.

Journal ArticleDOI
TL;DR: In this article, a new scheme of digital speckle pattern interferometry (DSPI) for observing the entire process of dynamic deformation from the beginning of elastic deformation to the end of plastic deformation at fracture is proposed.
Abstract: A new scheme of digital speckle pattern interferometry (DSPI) for observing the entire process of dynamic deformation from the beginning of elastic deformation to the end of plastic deformation at fracture is proposed. Interesting deformation processes which consist of spatial mode division of fringes caused by plastic deformation and stress relaxation were clarified by simple experiments.

Journal ArticleDOI
TL;DR: In this article, the authors describe the application of TV holography, also known as electronic speckle pattern interferometry (ESPI), to the examination of wall paintings.
Abstract: The authors describe the application of TV holography, also known as electronic speckle pattern interferometry (ESPI), to the examination of wall paintings. The equipment usesfibre-optic illumination and a solid-state camera connected to a computer. Images made after the wall painting has been warmed slightly with an infrared lamp are compared with reference images; differences in the speckle pattern can be used to identify cracks and subsurface detachments. The system is robust and portable, allowing it to be used for the in situ investigation of wall paintings, including those exposed externally. It can also be used to monitor the condition of the work of art over time and to evaluate the success of any treatment.

Journal ArticleDOI
TL;DR: In this paper, a 3D electronic speckle pattern interferometer was adapted to the testing machine for measuring the spatial displacement field at the surface of the cruciform wooden specimen. But this measurement was performed in a single step and at each step three interferograms were taken.

Journal ArticleDOI
TL;DR: In this paper, an optical fiber based, speckle shearing interferometer for out-of-plane time-averaged vibration analysis is described, which uses a highly birefringent optical fibre to illuminate a test object with equal intensities of light guided by the orthogonal polarization eigenstates of the fibre.
Abstract: An optical fibre based, speckle shearing interferometer for out-of-plane time-averaged vibration analysis is described. The technique uses a highly birefringent optical fibre to illuminate a test object with equal intensities of light guided by the orthogonal polarization eigenstates of the fibre. Phase modulation between the sheared images is readily achieved, without mechanical movement of components, by sinusoidally strain modulating the relative phase of the polarization states in the fibre. A Wollaston prism is used to obtain two sheared images with adjustable shear.

Journal ArticleDOI
TL;DR: In this paper, the spectrum of intensity fluctuations contains a high-frequency peak in the absence of a subsidiary reference wave at nonsmall angles of speckle observation, interpreted as a new type of manifestation of the Doppler effect.
Abstract: Based on theoretical and experimental analyses, it is shown that the spectrum of intensity fluctuations contains a high-frequency peak in the absence of a subsidiary reference wave at nonsmall angles of speckle observation. This phenomenon, interpreted as a new type of manifestation of the Doppler effect, is usual only for the case of strongly focused coherent beam scattering. The possibilities for using the observed effect in the measurements of blood and lymph flows in narrow native capillaries are discussed. The traditional Doppler method using strongly focused Gaussian beam scattering is also considered. It is shown that the frequency position of the Doppler peak in the spectrum of intensity fluctuations is defined not only by the angle of speckle observation but also by the relation between the waist beam diameter and the average size of flow inhomogeneities. This result was experimentally verified. It is concluded that the Doppler method of blood flow measurement using strongly focused Gaussian beam diffraction should be revised.

Journal ArticleDOI
TL;DR: The main result is that the fringes are obtained with high contrast and low Speckle noise, if the speckle size is selected by the optical system so as to be smaller than the pixel size.
Abstract: Characteristics of the fringe pattern detected by an electronic speckle pattern interferometer, in conditions in which a test object deforms in an arbitrary direction and the speckle intensity is detected over a pixel area in the TV camera to be used, have been investigated from two aspects: speckle noise reduction and fringe contrast. The main result is that the fringes are obtained with high contrast and low speckle noise, if the speckle size is selected by the optical system so as to be smaller than the pixel size. This result is applicable to highly accurate measurements of the out-of-plane displacements of the test object, whose in-plane displacement is small.

Journal ArticleDOI
TL;DR: In this paper, a phase-shifting digital speckle pattern interferometer (DSPI) has been calibrated using a Michelson interferer, which is shown live on the TV monitor and then processed slice by slice after recombination following their recording sequence.
Abstract: A phase-shifting digital speckle pattern interferometer (DSPI) has been calibrated using a Michelson interferometer. Calibration consists in measuring phase shifts generated by piezoelectric transducers (PZTs) and also to determine drift of the phase with time in the interferometer arms. The calibration fringes are displayed live on the TV monitor and then processed slice by slice after recombination following their recording sequence (PZT voltage or time). Dark fringes are detected to compute the wavelength with good accuracy (λ/170 theoretical) and the optical path difference is stored in a datasheet for every slice. This leads to the measurements of the drift and the calibration of the phase shifters with an accuracy about λ/20. Out-of-plane and in-plane optical fiber DSPIs have been successfully characterized using the same algorithm. The method presented also enables inexpensive data processing. Moreover the real-time measurement of the interferometer drift enables feedback loop active control during DSPI measurements.

Proceedings ArticleDOI
23 Aug 1995
TL;DR: In this paper, an iterative deconvolution algorithm is proposed to recover the target distribution when the point spread function is either unknown or poorly known. But this algorithm does not require the use of an unresolved target for point spread functions calibration.
Abstract: We present an application of an iterative deconvolution algorithm to speckle interferometric data. This blind deconvolution algorithm permits the recovery of the target distribution when the point spread function is either unknown or poorly known. The algorithm is applied to specklegrams of the multiple star systems, and the results for (zetz) UMa are compared to shift-and-add results for the same data. The linearity of the algorithm is demonstrated and the signal-to-noise ratio of the reconstruction is shown to grow as the square root of the number of specklegrams used. This algorithm does not require the use of an unresolved target for point spread function calibration.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Proceedings ArticleDOI
23 Jun 1995
TL;DR: In this paper, a thin-walled pressure vessel (satellite tank) is loaded by changing the internal pressure and the resulting deformation field is measured quantitatively, and defects in the wall become visible as local peaks in the global deformation fields.
Abstract: Digital recording and numerical reconstruction of holograms is a new method of laser metrology: two or more Fresnel holograms, which represent different loading states of the object, are generated directly on a CCD-target and stored electronically. In contrast to speckle interferometry, no lens or other imaging device is used. The reconstruction is done from the digitally stored holograms with numerical methods. For both states, the intensity as well as the phase of the object wave can be calculated in the reconstruction process. This makes it possible to calculate the interference phase directly from the holograms, without generating an interference pattern. In this paper, applications of digital holography in the field of nondestructive testing are presented. A thin-walled pressure vessel (satellite tank) is loaded by changing the internal pressure and the resulting deformation field is measured quantitatively. Defects in the wall become visible as local peaks in the global deformation field.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Journal ArticleDOI
TL;DR: In a regime of increasingly sophisticated and impressive instrumentation designed for high‐resolution imaging, there is still an important role for the single‐aperture passive technique of speckle imaging.
Abstract: This article discusses current research in speckle interferometry and speckle imaging in astronomy. These techniques continue to have a significant impact on problems such as stellar formation, stellar masses, and planetary astronomy. In a regime of increasingly sophisticated and impressive instrumentation designed for high-resolution imaging, there is still an important role for the single-aperture passive technique of speckle imaging.


Journal ArticleDOI
TL;DR: A new, handy method to evaluate phase data from fringe patterns produced by electronic Speckle-pattern interferometry is proposed, capable of evaluating phase data by simply taking speckle images and performing arithmetic operations on them.
Abstract: A new, handy method to evaluate phase data from fringe patterns produced by electronic speckle-pattern interferometry is proposed. The method is capable of evaluating phase data by simply taking speckle images and performing arithmetic operations on them. No extra optics or phase modulation is needed. Experiments have been carried out to prove the validity of the principle and demonstrate the capability of applications to practical deformation analyses.

Journal ArticleDOI
TL;DR: In this article, an in-plane deformation inspection system, which offers automatic acquisitions of interferograms at different stages of a test, is applied to the evaluation of some mechanical characteristics of masonry components.
Abstract: Electronic speckle pattern interferometry (ESPI) can be a powerful tool for efficient non-destructive testing and evaluation of micro-deformations of materials and structures. Unlike traditional transducers, ESPI requires no direct contact with the inspected object and the full-field visualization provides better understanding of the surface behaviour. The authors describe an in-plane deformation inspection system, which offers automatic acquisitions of interferograms at different stages of a test. The system is applied to the evaluation of some mechanical characteristics of masonry components. Qualitative and quantitative results are obtained and a comparison with traditional inspection methods is presented.


Journal ArticleDOI
TL;DR: It is shown that the speckle nature of electronic Speckle pattern interferometry images can be reduced in quasireal time with the use of only three consecutive video images, and by use of additive-subtractive phase modulation processing the technique is essentially insensitive to environmental noise, and distortion of fringes does not occur.
Abstract: It is shown that the speckle nature of electronic speckle pattern interferometry images can be reduced in quasireal time with the use of only three consecutive video images. By use of additive-subtractive phase modulation processing the technique is essentially insensitive to environmental noise, and distortion of fringes does not occur. By further removing the random speckle phase we show, using speckle statistics, that the number of dark speckles in the resulting fringe pattern is close to zero.

Journal ArticleDOI
S.Y. Wu1, Yuwen Qin1
TL;DR: In this article, an experimental method is described which can measure the directions and magnitudes of residual stresses in metal, using large shearing speckle interferometry combined with the hole drilling method to measure the surface deformation around the hole.

Journal ArticleDOI
TL;DR: In this paper, a detailed SNR analysis of estimating the modulus of an object's Fourier spectrum from turbulence-distorted images is described, taking into account the proper temporal correlation properties of the atmosphere and the spatial frequency being estimated, as well as the interframe correlations that degrade the SNR improvement factor from the ideal case of m.
Abstract: In the past 10 years astronomical image reconstruction based on a variety of speckle techniques has become a popular means of enhancing and improving the resolution of turbulence-degraded images. These techniques are based on the Fourier processing of a large number of turbulence-degraded snapshots or frames of the irradiance in the system’s image plane. The number of snapshots needed is largely a function of the signal-to-noise ratio (SNR) of the Fourier components of a single snapshot. Estimating these Fourier components is hampered by the inherent noise induced by the photon detection process and the random effect of the turbulent atmosphere. In most cases the SNR is much less than unity, and many frames are averaged to improve the overall SNR. It is well established that if the frames are uncorrelated then the SNR improves in comparison with the single-frame SNR by a factor of m, where m is the number of frames averaged. This fact implies that the smallest exposure time possible is desirable in order for m to be maximized for a given observation time. On the other hand, because of finite photon flux levels and read noise effects it can be shown that the exposure time should be increased at the cost of reducing m. Results from a detailed SNR analysis of estimating the modulus of an object’s Fourier spectrum from turbulence-distorted images are described. Unlike previous analyses, this work takes into account the proper temporal correlation properties of the atmosphere and the spatial frequency being estimated as well as the interframe correlations that degrade the SNR improvement factor from the ideal case of m.