Simulation of synthetic aperture sonar performance under experimentally measured environmental fluctuations

In June 2003, NRL conducted a series of coherence measurements in very shallow water (8 m depth) off the coast of Panama City, FL under a wide range of ocean conditions. Low-frequency (1–10 kHz) and high-frequency (10–200 kHz) measurements were taken. The results show appreciable variability even during fairly calm conditions. This paper will report on the effects of this experimentally measured variability on the performance of a simple computer-simulated synthetic aperture sonar (SAS). SAS works by rapidly and repeatedly pinging a target from a moving acoustic array platform. If the underwater acoustic environment changes appreciably between pings, random phase errors are introduced on the individual SAS receiving elements, with the result that the SAS image might be significantly degraded. The use of a computer-modeled SAS allows for the investigation of these effects in the absence of such phenomena as random receiver motion (motion compensation) or specific auto-focusing algorithms. [Work supported by the ONR Program Element No. 62435N.]