Numerical evaluation of the M parameter for direct detection ladar

Laser Radar Technology and Applications XIX; And Atmospheric Propagation XI

2014

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Atmospheric turbulence produces intensity modulation or "scintillation" effects on both on the outward laser-mode path and on the return backscattered radiation path. These both degrade laser radar (ladar) target acquisition, ranging, imaging, and feature estimation. However, the finite sized objects create scintillation averaging on the outgoing path and the finite sized telescope apertures produce scintillation averaging on the return path. We expand on previous papers going to moderate to strong turbulence cases by starting from a 20kft altitude platform and propagating at 0 o elevation (with respect to the local vertical) for 100km range to a 1 m diameter diffuse sphere. The outward scintillation and inward scintillation effects, as measured at the focal plane detector array of the receiving aperture, will be compared. To eliminate hard-body surface speckle effects in order to study scintillation, Goodman's M-parameter is set to 10 6 in the analytical equations and the non-coherent imaging algorithm is employed in Monte Carlo realizations. The analytical equations of the signal-to-noise ratio (SNRp), or mean squared signal over a variance, for a given focal plane array pixel window of interest will be summarized and compared to Monte Carlo realizations of a 1m diffuse sphere.

Section: Speckle Effects Elimination For Scintillation Studiesmentioning

confidence: 99%

Outward atmospheric scintillation effects and inward atmospheric scintillation effects comparisons for direct detection ladar applications

Laser Radar Technology and Applications XIX; And Atmospheric Propagation XI

2014

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“…"M spkl " is Goodman's M parameter [1][2][3][4][5] for vacuum propagation. The mean of "k" is denoted as N S , where "S" denotes signal, as opposed to dark-counts or background-counts which sum together producing a mean denoted by "N n " corresponding to "noise."…”

Section: Photo-electron Statistics Reviewmentioning

confidence: 99%

Receiver-operating characteristic for several multiple hypothesis range-rate filter algorithms

Laser Radar Technology and Applications XV

2010

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Several multiple-hypothesis range-rate algorithms are investigated to determine initial target acquisition capabilities of a direct detection ladar operating under low photo-electron return conditions. During initial acquisition of an object, the location of the object is not known, therefore the ladar returns cannot be simply summed in order to improve detection statistics. Analogous to classical radar multiple hypothesis algorithm approaches a "shift and sum," a "shift and accumulate," and a "numerically shift and histogram" algorithm are investigated. The probability density function for the maximum of the multiple-hypothesis range-rate algorithm matrix output is developed so that a threshold crossing probability can be determined and a "detection" declared (receiver-operating-characteristic). This is expressed as a function of false alarm rate which is a function of the number of ladar returns processed in the acquisition process and the length of the acquisition window.

“…v(t)=h(t-t1) (5) where h(t) is the impulse response of the detector and the electronics, and the t1 are random points in time due to the negative-binomial process described in (4) and its Poisson or Bose-Einstein limits. For a fixed counting time, the number of t1 photo-electron events is "n" with pdf ps(n) given in (4).…”

Section: Detector and Electronic Shot-noise Effectsmentioning

confidence: 99%

Three-dimensional and two-dimensional sequence spatial-frequency domain processing of speckled ladar images for automatic target recognition

Hart

1999

SPIE Proceedings

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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 microradians, there are generally at least a few angular pixels "on target." In addition, for narrow pulse (-1 ns) 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" size. This is known as "range resolved angle-angleintensity" ladar.In a previous paper we transformed this 3D-matrix image into the spatial-frequency domain using 3D-Fourier transforms and followed conventional 2D template correlation techniques to perform target recognition and identification. During this previous study, it was noted that the 2D range-bins could be placed in sequence and 2D filtering used on these synthetic images. Results of 3D and 2D-sequence target correlators using the "joint transform correlator," "the inverse filter," the "phase-only matched-filter," the "binary phase-only filter," and the classical "matched filter" are presented here. Far-field test data using conical shaped targets are used to study the 3D and 2D 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 reviewed as well. These 3D or 2D-sequence template correlators 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.