Synthetic Aperture Sonar (SAS) provides a large improvement in azimuth resolution compared with conventional side-scan sonar. This improvement is achieved by combining the data from a number of pings to synthesise a long virtual receive array. Difficulties in forming a SAS image arise from the need for complex processing techniques and accurate knowledge of platform position. A number of synthetic aperture imaging (inversion) algorithms have been developed for both Synthetic Aperture Radar (SAR) and SAS. The vast majority of these techniques work in the frequency domain and are best suited to processing data formed from a nominally linear, evenly sampled synthetic aperture. An exception to this is the exact time domain technique; however this has a computational complexity of O(N~3) so is prohibitively slow even for small data sets. Fast Factorised Back Projection (FFBP) is an inversion technique recently developed for SAR. FFBP overcomes many of the problems associated with other inversion methods in that it can cope with general aperture geometry, is fast, and has a very low memory requirement. This paper discusses the application of FFBP to SAS, along with using the framework of FFBP to develop motion estimation techniques. Results using real data are presented.
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