The effect of multi-path on synthetic aperture sonar image statistics

Abstract

The K-distribution shape parameter has been shown to be a useful metric of seafloor reverberation statistics. Using this metric, synthetic aperture sonar (SAS) data collected during the Office of Naval Research sponsored SAX04 experiment in the Gulf of Mexico during October 2004 has been processed to examine image statistics as a function of range from the sonar. SAS images are unique in that the resolution cell size does not increase with range as for traditional sonar. Analysis of the SAX04 data has shown that in spite of the fixed resolution cell size, shape parameter estimates were found to increase with range from the sonar. The increase can be attributed to multi-path propagation. At increasing distance from the sonar, scattered returns arising from additional propagation paths arrive in a specified time window, with the result that two or more resolution cells are contributing, which leads to a larger estimate of the shape parameter than would be expected when only the direct path contributes. Model results using the sonar system geometry and seafloor scattering theory will be used to demonstrate this effect. [Work supported by ONR Codes 321 and 333. First author supported by a National Defense Science and Engineering Graduate Fellowship.]