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Image Sharpening by Selecting Number of Echoes in ISAR Imaging

An algorithm is developed to sharpen the image by selecting the number of echoes in ISAR imaging. Entropy is used to measure the sharpness of the image: smaller entropy means larger sharpness. The number of echoes is selected to minimize the entropy of the image. In the optimization, the azimuth discrete Fourier transform of each round is computed from the azimuth discrete Fourier transform of last round. This improves the computational efficiency significantly. The results of field data indicate the effectiveness of this algorithm.