Detection of Coherent Scatterers in Synthetic Aperture Sonar Using Multilook Coherence

Synthetic aperture sonar (SAS) is the reference technique for high-resolution acoustic imaging of the seabed. Unlike synthetic aperture radar (SAR), SAS suffers from insufficient accuracy of position, speed of sound, and terrain knowledge. This leads to the need for automated assessment of SAS image quality. Multilook coherence is a technique for detecting coherent scatterers which can be used to assess image quality. In this paper, we describe different ways to calculate multilook coherence. We test the techniques on real data collected by a HUGIN autonomous underwater vehicle carrying a HISAS interferometric SAS. We rate the different coherence techniques by evaluating the suitability of the candiate coherent scatterers they produce. The candidate technique that produces best suited candiates is the multilook coherence factor using a large number of looks per dimension.