Hughes Aircraft Company

Ramesh Rampertab

Robert T Frankot

A method of providing accurate elevation data from three or more complex SAR images. A SAR vehicle is operated to produce a number of SAR images at different grazing angles. The present method provides precise elevation maps derived from the SAR images. In a multiple channel variant of the present invention, more than two antennas collect SAR data from various grazing angles, increasing sensitivity while resolving the ambiguity problem in a mathematically optimum manner. A multiple pass variant of the present invention collects data from more than two passes, and from various grazing angles (interferometric 'baselines'). The multiple pass approach and associated processing preserves the high sensitivity of the long-baseline available from dual pass IFSAR while resolving the ambiguity problem in a mathematically optimum manner. Accuracy and ambiguity resolution are improved with each additional pass or channel. The method processes raw SAR data to produce a plurality of complex images therefrom. The complex images are processed to produce a plurality of linear phase matched complex images and predetermined processing parameters. The plurality of linear phase matched complex images are then processed to produce a elevation map. The plurality of linear phase matched complex images are produced by matching noise power contained in each of the complex images to normalize the images to compensate for differences in gain of the systems from scan to scan, matching linear phase values of each of the complex images to correct for phase differences by estimating phase matching parameters for each of the complex images, estimating a phase-difference scale factor for each of the complex images, and ordering each of the complex images in terms of increasing phase difference scale factors. The linear phase values of each of the complex images are matched by computing a pairwise interferogram for adjacent complex images, summing sample-pair products of the interferogram to estimate the linear phase thereof, and computing the phase of the summed sample-pair products. The elevation map is computed by computing an initial elevation map using conventional IFSAR techniques applied to a pair of complex images, estimating additive phase correction values for each of the linear phase matched complex images, and estimating elevation values by maximizing the magnitude of the complex weighted sum of M complex images or complex interferograms, where the weights include the phase attributable to the estimated elevation to produce the elevation map.

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Los Angeles, CA, United States of America

Ramesh Rampertab