Abstract
This presentation gives an overview of the state-of-the-art in side-looking acoustic imaging using synthetic aperture techniques. It starts with the development of aperture synthesis, gives the historical background of synthetic aperture sonar (SAS), and then describes the salient differences between that and its electromagnetic equivalent; synthetic aperture radar (SAR). This paper takes a broad view of how SAS developed and where these developments occurred. We look at the past (with close attention paid to the patent literature), the present, as well as to hazard some guesses as to the future. Problems that are currently being addressed by various SAS research groups include efficient algorithms for multiple hydrophone array systems, difficulties with ground truthing of images, yaw and sway motion compensation of the sonar platform, multipath suppression, iterative autofocus techniques for residual motion error as well as to counteract medium turbulence. Since the number of SAS systems deployed is likely to be limited in the near future, the need for more and better modelling of the environment and the sonar system as well as more accurate simulation tools are discussed. In the future, accounting for temporal Doppler at higher tow speeds, obtaining full 3-D terrain imaging using bathymetric SAS, and maintaining full diffraction limited resolution for arbitrary path loci will be likely. SAS has now come of age. It is no longer a case of if it works but how can we make it work better and what sort of end user will employ it profitably.
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