The Impact of the Temporal Variability of Seafloor Roughness on Synthetic Aperture Sonar Repeat–Pass Interferometry

In this paper, we review past work and present new analysis of the temporal variability of seafloor roughness and how this variability impacts synthetic aperture sonar (SAS) repeat-pass interferometry. The new work presented here uses a model based on first-order perturbation theory for acoustic interface scattering to link the complex coherence of SAS images taken at different times to the decorrelation of seafloor-roughness spectral estimates. Results are assessed through a comparison of decorrelation values generated by processing seafloor roughness data recorded by a digital photogrammetry system and complex SAS image data acquired with a translating source/receiver rail assembly. These data sets were collected on sandy seafloors off the western coast of Florida as part of the U.S. Office of Naval Research (ONR)-sponsored 2004 Sediment Acoustics Experiment (SAX04). Our results show that the diffusion model for changes in sediment roughness developed previously [ D. R. Jackson , IEEE J. Ocean. Eng., vol. 34, no. 4, pp. 407-422, Oct. 2009] provides an excellent fit to our data over a large range of spatial frequencies. In both the past work and new analysis, decorrelation was found to be frequency dependent with e-folding times (i.e., decay constants) of hours to days, setting a limit on reasonable time frames for successful repeat-pass coherent change detection.

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