On using multi-look synthetic aperture sonar analysis for the investigation of scattering mechanisms

Abstract

Multi-look coherence explores the information content of synthetic aperture sonar (SAS) images by splitting the total angle and frequency spectral bandwidth of a complex SAS image into sub-bands. In the presence of a random distribution of surface or volume scatterers, the spectral coherence is proportional to the degree of overlap in sub-bands of the SAS image. Consequently, for a perfectly random distribution of scatterers, the spectral coherence should be zero when the sub-bands do not overlap. If the scatterer distribution deviates from this basic random distribution, the spectral coherence may be non-zero for special cases that would be related to scattering from specific structures such as points or facets. For that reason it appears to be possible to separate coherent features from the random scattered background signal using spectral coherence, suggesting possibilities for detecting and/or characterizing objects (especially in low signal-to-reverberation situations). In this talk, we will discuss the concept and the utility of using the complex coherence between a series of sub-look SAS images to investigate different scattering mechanisms as well as show examples of the technique using real and modeled SAS data. [Work performed under ONR Grants N00014-16-1-2469 and N00014-16-1-2313.]