Improving Swath Sonar Water Column Imagery and Bathymetry With Adaptive Beamforming

Modern swath sonar is a mature technology today and has reached a very high level of sophistication including techniques to increase area coverage rate, data quality, and resolution. There is, however, often a need to explore features at the limit of what is resolvable. It is, therefore, of interest to consider alternative signal processing techniques for a given physical system. For the traditional delay-and-sum (DAS) beamformer there is a tradeoff between angular resolution and sidelobe suppression. Using either the Capon or the low complexity adaptive (LCA) beamformer, the water column edge definition, sidelobe level, and resolution are improved compared to a moderately weighted DAS beamformer. These improvements are similar to the recent results for sector-scanning sonar. This leads to improved performance for the amplitude-based center-of-gravity bottom detector. The Capon beamformer performs best, while the LCA beamformer has a large part of the improvement with higher robustness and easier implementation. We use simulations to show the improvements of the adaptive beamformers from nadir up to 42
^o
across track, and validate the results using field data. The improvements in the water column increase the separation between features and noise, and collapse the apparent size of features down to more realistic dimensions. These improvements allow the adaptive beamformers to reveal features that are hidden for the DAS beamformer.