Raytheon Company

Michael Yih-Hwa Jin

Chi-Yung Chang

An algorithm for deriving improved navigation data from the autofocus results obtained from selected image blocks in a wide-beam synthetic aperture radar (SAR) image. In one embodiment the navigation error may be approximated with a vector of low-order polynomials, and a set of polynomial coefficients found which results in a good phase error match with the autofocus results. In another embodiment, a least squares solution may be found for the system of equations relating the phase errors at a point in time for selected image blocks to the navigation error vector at that point in time. An approach using low sample rate backprojection () initially to select suitable image blocks, and full sample rate backprojection () for the selected image blocks, followed by full sample rate backprojection () for the image, using the improved navigation solution, may be used to reduce the computational load of employing the algorithm.

Wide beam SAR focusing method using navigation solution derived from autofocus data

Range and Doppler ambiguities are common in radar, lidar, and acoustic systems. Resolving these ambiguities is important to achieve desirable geolocation and image quality performance in these systems. A new method is described to iteratively resolve the ambiguities. For Doppler ambiguity applications, a first PRF value and an initial Doppler frequency search window are selected. A new PRF is determined based on the ratio of the initial search window to the first PRF. The radar data of the first pair of PRF's is used to determine two modulo Doppler estimates. The modulo Doppler estimates are used to determine a new Doppler estimate with a confidence interval smaller than the first search window. The ratio of the new Doppler search window to the first PRF, is used to determine the next PRF. This process is iterated until the new Doppler search window is less than the first PRF.

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Arcadia, CA, United States of America

Michael Yih-Hwa Jin