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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.