Statistics of speckle propagation through the turbulent atmosphere

Lee, Myung Hun; Holmes, J. Fred; Kerr, J. R.

doi:10.1364/josa.66.001164

Cited by 69 publications

(13 citation statements)

References 34 publications

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“…The Green function in the turbulent atmosphere has the form'2"4 G(z,O;,)=G0(z,O;i,)exp(%(r,r)+iS(r,r)), (8) where and S is the log-amplitude and phase fluctuations of a spherical wave. In a weak scintillation regime, when Rytov variance ?…”

Section: (7) Az Azmentioning

confidence: 99%

<title>Enhanced backscatter and turbulence effects on pupil-plane speckle imaging system</title>

Belen'kii

2002

SPIE Proceedings

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We investigate the effects of turbulence on pupil-plane speckle imaging system that has been proposed to provide highresolution images of a low Earth orbit (LEO) satellite using laser illumination. We present a theory and numerical results for the normalized speckle covariance for one-dimensional object in the turbulent atmosphere and demonstrate that turbulenceinduced anisoplanatism and scintillation degrades this characteristic. The effect of anisoplanatism is associated with the finite size of a satellite. Due to a finite satellite dimension, optical waves arrive at the receiver from different directions determined by the angular size of the satellite and sample different turbulence. The resulting phase difference degrades the normalized speckle covariance. This effect is similar to the degradation of the performance of adaptive optics system caused by turbulence-induced anisoplanatism when a reference beacon is separated from the target at some distance. Scintillation on the downlink path also degrades the normalized speckle covariance. It causes the dc-and ac-components of the speckle correlation to exceed their values in a free space when the separation between the observation points is smaller than the spatial correlation scale of the scintillation. At the same time, both components are decreased for large separations when scintillation is uncorrelated. This reduces the normalized speckle covariance and can degrade the performance of a pupilplane speckle imaging system. The effect of scintillation on the dc-and ac-components of the speckle correlation is similar to the enhanced backscatter phenomenon, in which the average power of the laser return in the strictly backward direction in the turbulent atmosphere exceeds its value in free space. For a small object, the effect of scintillation on the speckle covariance predominates. The speckle statistics for the space-to-ground scenario differ from that for the horizontal path.

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Section: (7) Az Azmentioning

confidence: 99%

<title>Enhanced backscatter and turbulence effects on pupil-plane speckle imaging system</title>

Belen'kii

2002

SPIE Proceedings

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“…Round-trip passage ladar scintillation from resolved targets has been well characterized in the literature by Holmes and Gudimetla [12][13][14][15] . They found that a "two-parameter K distribution" irradiance distribution fits the data and theory of round-trip propagation effects well: …”

Section: Round-trip Turbulence Effects (Endo-atmospheric Scenarios)mentioning

confidence: 99%

“…Complicated analysis [12][13][14][15] can calculate the aperture averaged normalized intensity variance, but it is possible to make a simple curve fit to data, and the aperture averaging factors …”

Section: Round-trip Turbulence Effects (Endo-atmospheric Scenarios)mentioning

confidence: 99%

The United States Homeland Defense Against International Terrorist

Dochnal¹

2001

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Direct-detection laser radars can measure the range and the intensity returns from a target, with or without clutter, for each part of the target resolved in angle by the optical system. Because the ladar's angular resolution is in micro-radians, there are generally at least a few angular pixels "on target." In addition, for narrow pulse ladar systems, there may be ten or so sequential intensity measurements in range per pixel as the laser pulse propagates down the target's surface. The output image is, therefore, potentially a three dimensional "cube" of intensity measurements and quantized in the range axis by the range-bin size or "voxel." This is known as "range resolved angle-angle-intensity" ladar, and one such system is being built by BMDO under the DITP effort.Transforming this 3D-matrix image into the spatial-frequency domain using 3D-Fourier transforms, we have followed conventional 2D template-correlation techniques to perform target recognition and identification. Results of target image correlations using the "joint transform correlator," "the inverse filter," the "symmetric phase-only matchedfilter," and the classical "matched filter" among others are presented. Also, projection of the 3D-matrix image onto the x-y, x-z, and y-z planes allows the use of conventional (2D) correlators, but their outputs must be combined. Simulated far-field test data using conical shaped targets are presented to study the 3D correlators, and the effects of laser speckle are discussed. Recent developments in negative-binomial driven shot-noise effects in range-resolved direct-detection ladar are outlined as well. We note that 3D template correlation may supplement or refine less computationally intensive algorithms such as total signal, range-extent, x-z, y-z, and x-y plane image centroid estimation, and image moments. INTRODUCTIONThere are many two dimensional image processing algorithms useful in automatic target recognition and identification that can be found in the literature. We summarize some of these in Section 3.0 as developed by the passive sensor community, but now we extrapolate them to three dimensions: elevation, azimuth, range, and intensity per voxel. Even with a single range measurement per elevation / azimuth pixel (current tactical ladars), the effects of laser speckle must be accurately modeled. Recent work has allowed the numerical evaluation of the speckle "M" parameter for arbitrary source region, illumination irradiance, and receiver aperture. These speckle effects are briefly summarized in Section 2.0. In addition, as the photons are detected by a photon-counting photo-multiplier tube, the detector's response and the electronic's bandwidth result in a classical "shot-noise" impulse-response summation process. This is also reviewed in Section 2.0 based on state of the art photomultplier tube detector data. Form SF298 Citation DataReport Date ("DD MON YYYY")

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“…In recent years it has been investigated in depth and the processing based on speckle interferometry [2,3] and speckle holography [4] allows diffraction-limited star images to be obtained, despite the presence of turbulence . The speckle effects are important in remote sensing of the atmosphere, in coherent imaging through the atmosphere and in radar and coherent optical adaptive systems (see, for example, [3][4][5][6][7]) .…”

Section: 1 General Considerationsmentioning

confidence: 99%