Adaptive phase estimation filter in long range synthetic aperture sonar interferometry

Synthetic aperture sonar (SAS) interferometry is a technique for very high resolution imaging and mapping of the seabed. In SAS interferometry, the seabed depth estimation performance is a function of the system, the geometry, the signal-to-noise ratio (SNR) and the filter size, equivalent to the achieved horizontal resolution. A strong driver for SNR is the imaging range and grazing angle. The variation of these parameters over a typical SAS swath gives rise to a large variation in the depth estimation performance. To mitigate the negative effect of this, we suggest to use an adaptive phase estimation filter size, such that the standard deviation of the depth estimate is proportional to the horizontal resolution. We demonstrate the suggested adaptive filter size method on long range data collected using a HUGIN Superior autonomous underwater vehicle (AUV) equipped with a HISAS 1032 Dual receiver interferometric SAS. Our technique increases the valid area coverage when the SNR is marginal, at the expense of reduced horizontal resolution.