Recent analysis of Synthetic Aperture Sonar data collected during the Office of Naval Research sponsored SAX04 experiment in the Gulf of Mexico during October 2004 has shown that the processed image has varying amplitude statistics as a function of range. Since synthetic-aperture sonar maintains a constant range-independent resolution cell size, unlike traditional sonar systems, one would expect that the statistics of the image would be based solely on the seafloor properties. The K-distribution shape parameter was estimated as a function of range and increases at discrete ranges corresponding to the onset of multi-path propagation (low shape parameter values represent a heavy tailed distribution). At these points of increase in shape parameter, scattered returns arising from additional propagation paths arrive with the result that two or more parts of the seafloor are contributing to the same sonar resolution cell, which leads to a larger K-distribution shape parameter than would be expected when only the direct path contributes. Model results using the sonar system geometry and interface scattering theory will be used to illustrate this effect. [Work supported by ONR Codes 321 and 333. First author supported by a National Defense Science and Engineering Graduate Fellowship.]
