The United States Homeland Defense Against International Terrorist

Abstract

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")