Statistics of synthetic aperture sonar image resolution degradation.

Abstract

Synthetic aperture sonar (SAS) image statistics can often be characterized by a probability density function with a heavier tail than the expected Rayleigh distribution. The K‐distribution shape parameter can be used as a metric of non‐Rayleighness, with physical ties to both seafloor properties and sonar parameters. Recent results have shown that increasing the resolution cell size, or degrading the resolution of the image, produces images with statistics tending toward Rayleigh (i.e., a higher K‐distribution shape parameter). In general, a doubling of the resolution cell area results in a doubling of the K‐distribution shape parameter. A caveat to this generalization is the orientation of the sonar system to any features that may exist on the seafloor (i.e., sand ripples). In such a situation, image statistics may continue to be significantly non‐Rayleigh for certain orientations in spite of resolution degradation. SAS images of seafloors with various bottom types and feature orientations collected with an AUV by the Naval Surface Warfare Center Panama City Division have been postprocessed to analyze changes in image statistics as the image resolution is degraded. Results of the image degradation on statistics will be discussed. [Work supported by ONR Grant Nos. N00014‐04‐1‐0013 and 1N00014‐06‐1‐0245, and Code 32.]