Showing papers on "Speckle imaging published in 1987"

ICCD Speckle Observations of Binary Stars. IV. Measurements During 1986-1988 from the Kitt Peak 4-m Telescope

Abstract: Six-hundred twenty-one observations of 487 binary star systems, observed by means of speckle interferometry with the 4 m telescope on Kitt Peak, are presented. The median separation determined in these measurements, made mainly during 1989 and 1990, was 0.21″. These data include an additional component to a known wide pair and a previously undetected component to a high-velocity star

Electro-Optic Holography System For Vibration Analysis And Nondestructive Testing

Abstract: A TV system has been developed for detecting and displaying a two-dimensional hologram image that permits concomitant (real-time) hologram interferometry The optics employed are the same as for electronic speckle pattern interferometry (ESPI), wherein a uniform reference field interferes at zero offset angle with a speckled image of an object Rather than detecting spatial modulation to indicate interference, as in ESPI, this system modulates the phase of the reference beam by 120° between picture frames to vary speckle irradiance Each incoming frame is compared with the two previous frames, and only pixels that vary in brightness are passed as white pixels in the video output The use of binary-valued pixels allows inexpensive data processing at standard video rates

Measurement of difference deformation using speckle interferometry.

Abstract: An application of speckle interferometry is presented that allows one to compare the resistance to stress of two nominally identical specimens. The interference pattern gives contours of equal differences in displacements of the two stressed specimens. The method is briefly developed, and its experimental feasibility is demonstrated by comparing the deflections of two square plates clamped along the edges and subjected to centrally concentrated loads.

A relativistic jet from SN1987A

Abstract: Une interferometrie de speckle de cette supernova 5 a 7 semaines apres l'explosion a revele la presence d'un second objet seulement trois magnitudes plus faible que la SN elle-meme

Displacement Measurement by Image-processed Speckle Patterns

Abstract: The use of a commercial image-processing system in digital speckle-pattern interferometry is demonstrated. The possibilities of electronic-noise suppression and speckle-noise smoothing are discussed. Synthetic speckle patterns have been created and are shown to be useful in software development. Fringe skeletons have been extracted automatically from both synthetic and experimental correlation fringes giving accurate quantitative results.

Optically phase-locked electronic speckle pattern interferometer.

Abstract: The design, theory, operation, and characteristics of an optically phase-locked electronic speckle pattern interferometer (OPL-ESPI) are described. The OPL-ESPI system couples an optical phase-locked loop with an ESPI system to generate real-time equal Doppler speckle contours of moving objects from unstable sensor platforms. In addition, the optical phase-locked loop provides the basis for a new ESPI video signal processing technique which incorporates local oscillator phase shifting coupled with video sequential frame subtraction.

Heat Transfer Measurements in a Motored Engine Using Speckle Interferometry

Abstract: Gas-side temperature profile measurement in engines may provide valuable information regarding surface heat transfer as well as information on other fluid characteristics such as boundary layer thickness. Due to the typical cyclic variation of fluid variables in engines, profile measurement must be accomplished essentially instantaneously. This paper describes the use of speckle interferometry for acquiring such data. The advantages and disadvantages of the method are briefly described with respect to current spectroscopic and other interferometric techniques. The method has been applied to measure temperature profiles normal to the cylinder head in a motored two-cycle engine.

Automated fringe measurement in speckle photography

Abstract: An automated Young’s fringe processor for point filtering of speckle photographs is described. It automatically measures the magnitude and direction of displacements from fringe densities of less than twenty with good accuracies. Microcomputer-based, requiring <64K of memory, the system provides full automation by employing computer-controlled scanning.

Stellar speckle interferometry energy spectrum recovery by convex projections.

Abstract: A new method is described for recovering the object energy spectrum in stellar speckle interferometry. An initial division estimate is improved with a constrained iterative algorithm that uses projections onto convex sets. The technique is demonstrated to recover the energy spectrum out to frequencies where the signal-to-noise ratio is <1.

Phase closure with a rotational shear interferometer.

Abstract: A simple and efficient way is proposed for achieving phase closure in an optical telescope (to enable recovering Fourier transform phases that would otherwise be corrupted by atmospheric and instrumental errors), by means of rotational shear interferometry. In a rotational shear interferometer, one images the telescope aperture onto the interferometer and then interferes the aperture with itself in a rotated orientation. To achieve the maximum frequency content permitted by the telescope, the shear has to be 180 deg, but better dynamic range and SNR are possible for lower frequencies. Drawbacks of the proposed method compared to radio astronomy are noted, and different approaches are indicated as to how to collect and use the phase closure data. Phase closure can be realized on existing telescopes and existing interferometers with special modifications. Although not all base lines are possible, the extra constraints provided by the closure phases greatly reduce the ambiguity now existing in phaseless image reconstruction.

Astronomical speckle masking: image reconstruction by cross triple correlation.

Abstract: Speckle masking is a speckle method that is capable of reconstructing true diffraction-limited images from astronomical speckle interferograms. Image degradation caused by the atmosphere and by telescope aberrations can be overcome completely. Speckle masking is a solution of the phase problem in speckle interferometry. We propose a new, modified version of speckle masking that is based on cross triple correlation processing (or cross bispectrum processing) instead of autotriple correlation processing. The advantage of cross triple correlation processing is the fact that undesired photon bias terms in the average bispectrum of the speckle interferograms are overcome completely. We show computer simulations (astronomical magnitude of ~16m) that illustrate the feasibility of the method.

The use of a diode laser in an ESPI system

Abstract: The use of a diode laser in an ESPI system is reported. These lasers have considerable potential advantages over gas lasers in terms of convenience, cost and lifetimes, and may eventually replace the latter in this type of instrument.

A theoretical approach to the optimization of electronic speckle interferometry fringes with limited laser power

Abstract: Electronic speckle pattern interferometry (ESPI) is used to measure surface deformation, surface vibration, surface geometry and refractive index changes. In this paper, the way in which the available laser power should be used to optimize the clarity of the fringes obtained in ESPI systems using subtraction and a smooth reference beam (i.e. a reference beam derived directly from an expanded laser beam) is investigated. While the clarity of ESPI fringes is limited by the resolution of the video system used to obtain the fringes, it is shown that in general, the optimum fringe clarity is likely to be obtained when the f/number of the viewing system is set so that the speckle pattern is not fully resolved. The optimum setting in any given case is determined by the laser power available, the scattering properties of the object surface, the sensitivity of the camera and the spatial resolution of the video system; the relationship between these various parameters is derived.

Panoramic Holocamera For Tube And Borehole Inspection

Abstract: Examination of interior of cavities by holographic and/or speckle interferometry has been until recently of limited success because they all were based on conventional endo-scope principles, and, as a consequence, they had a restricted field of view. Cylindrical hologram recording techniques reconstruct images only from targets being inside, and not outside of the cylindrically folded recording medium, thus, the inner surface of the cavity cannot be measured by this technique. Using PDL optics developed at our laboratory the recorded cylindrical hologram reconstructs the entire inside of the cavity, thus, a 360° panoramic view of the interference fringes may be observed on the inside wall if double exposure technique was used, but even real-time holographic interferometry could be performed.

Phase-gradient reconstruction from photon-limited stellar speckle images

Abstract: The phase-gradient process for reconstructing stellar speckle images is implemented in a photon-address mode for application to images containing small numbers of photons. Comparisons are made with an address-mode Knox-Thompson process which show that the phase-gradient approach has computational advantages and better SNR performance. Reconstructions from simulated data and real data for the binary source Beta Delphinius are presented.

Astronomical image reconstruction via slit aperture telescope

Abstract: The interest of a ground based Slit Aperture Telescope (SAT) which operates with a long thin pupil has been underlined for applications in the field of high angular resolution observations by speckle-interferometric techniques. The SAT lies halfway between the Michelson stellar interferometer and the standard telescope with circular aperture. The authors present the principle of an image processing algorithm which could be used associated with a space-SAT for astronomical image reconstruction. A full coverage of the two dimensional Fourier plane of the astronomical object can be obtained by rotating the SAT around its optical axis. The method of image reconstruction is analogous to those used in computerized tomography and uses Fast Fourier Transform algorithm. The interest of the use of a rotating space-SAT among synthetic apertures is its capability of giving a reconstructed image of the astronomical object simultaneously in several light wavelengths, each colored image being comparable with the others for fruitful astrophysical applications. They suggest the ways to perform a ground based TPF for astronomical imagery.

Proposition of speckle probability imaging for stellar systems.

Abstract: Shows that the second probability density function of a stellar speckle pattern observed at the focus of a large telescope can be used for imaging double and multiple stars. A mathematical description of the second probability density function is made for a double star. The theoretical model makes use of a double statistic: the well known negative exponential law is assumed for the first probability density function of the speckle pattern for a single unresolved star, and Poisson statistics are used for photon detection.

Solar-granulation power spectra from speckle interferometry

Abstract: Granulation was observed with a CCD array at the SPO tower telescope in a quiet region near the solar center. The authors took time series of short-exposure (4 ms) pictures of a 14 sec by 14 sec region. Consecutive frames were separated by 0.55s in time. They applied Labeyrie's (1970) speckle-interferometry technique in order to recover power spectra of the intensity fluctuations at high spatial frequencies. The spectral-ratio technique was applied to correct for seeing attenuation of the power spectra. Signal up to a spatial frequency of 2.5 line pair per arcsecond was recovered, corresponding to a wave number of 22 M/m or 40% of the diffraction limit of the telescope under 1.3 arcsec average seeing conditions. A corrected rms granulation contrast of 0.127 + or - 0.01 was estimated, and an exponential falloff was observed of power density towards higher spatial frequencies.

Speckle grain noise in heterodyne techniques for holographic interferometry and speckle photogrammetry.

Abstract: Heterodyne techniques greatly improved the accuracy in readout systems for holographic interferometry and dual plate speckle photogrammetry, since the order of interference fringes is read via phase measurements. The limiting accuracy has been traditionally associated with scintillation noise. We discuss the existence of an additional intrinsic noise resulting from the random position of the speckles over the detector aperture (speckle grain noise). At variance with the predictions based on the scintillation noise, the accuracy remains finite even for perfectly correlated speckle fields.

Vacuum Speckle Interferometry For Long Term Monitoring Of In-Plane Strains At Defect Sites In Nuclear Pressure Tubes

Abstract: Vacuum speckle interferometry can be used for long term monitoring of local deformation and strain in the vicinity of hydride blisters as they evolve on the surface of hot samples of zirconium pressure tubes used in nuclear reactors. A video camera and frame grabber were used to provide computer access to the speckle pattern for fringe pattern extraction, image processing, and data analysis. Evidence was seen for strain around the blister during thermal expansion, and for change of strain with time when heated. Decorrelation could be seen at the blister edge as it dissolved at 340 C.

Statistical properties of the phase difference between two interfering speckle fields in speckle interferometry

Abstract: The statistical properties of the phase difference between the two interfering partially correlated and partially developed speckle fields were studied experimentally as a function of the intensity correlation coefficient. The gaussian statistics are assumed for the formation of speckle fields in the diffraction region and the correlation coefficient between the two speckle intensities is used to evaluate the phase difference. The standard deviation of the phase difference can be uniquely determined in the fully developed speckle field from the correlation coefficient of the two speckle intensities. However, it was found in the partially developed speckle field that the standard deviation of the phase difference between the two speckle fields cannot be uniquely determined from the correlation coefficient of the two speckle intensities.