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9 June 1994 Migration processing of spotlight SAR data
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Migration processing exactly accounts for the wavefront curvature over the imaged scene. Migration processing is therefore capable of forming high resolution SAR images when the data is acquired over a large synthetic aperture collection angle. Because migration processing requires phase compensation to a line corresponding to the nominal SAR flight path, the phase history is chirped over a very large bandwidth, requiring a very high sample rate to prevent aliasing in the frequency spectrum. The sample rate is determined by the size of the synthetic aperture collection angle. When migration processing is applied to a spotlight-mode SAR, this sampling rate can be much higher than that required for normal spotlight-mode processing. In this latter case, the phase history is motion compensated to scene center and the sample rate is determined by the spot size. Higher sampling rates result in large FFTs and may cause range ambiguity problems. ERIM has pursued the development of a variation on migration processing, which we call the Frequency domain Replication and Downsampling (FReD) algorithm, which enables the acquisition of data at normal spotlight-mode rates and which does not require the computation of FFTs any larger than those required for normal spotlight-mode processing. The FReD algorithm is based on the fact that when a discrete, aliased spectrum is replicated a sufficient number of times, the resultant spectrum will contain the desired signal spectrum. What we call the FReD algorithm is discussed in two articles by Prati, et al. Subsequent processing steps extract the desired portion of the spectrum to form an image. This paper will review migration processing, discuss the FReD algorithm and present expressions for the number of operations required for its implementation. Migration-processed, spotlight-mode SAR imagery derived from airborne collected data and demonstrating the utility of FReD are presented.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
August Golden Jr., Susan C. Wei, Kenneth K. Ellis, and Sreenidhi Tummala "Migration processing of spotlight SAR data", Proc. SPIE 2230, Algorithms for Synthetic Aperture Radar Imagery, (9 June 1994);

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