Long Range 3-D Reverberation and Scattering Modeling Methodology

Abstract

A methodology is being implemented for low frequency surface and bottom reverberation and scattering that uses 2-D and 3-D beam propagation similar to Gaussian beam (Porter & Bucker JASA 82(1987)) calculations in determining the source to scattering areas and the scattering areas to receiver paths. The approach makes use of source-receiver coupling tables. Temporal, acoustic intensity and direction information are filled into these tables by the propagation calculations from one or more sources to the scattering areas. Next, propagation from the scattering areas to the receivers are calculated, using a scattering function to couple to the receiver the various sources contributing to the acoustic energy impacting that area. Full ocean basins can be accommodated but at the expense of large tables and lengthy runs. The environmental factors used for the propagation calculations include five minute grided bathymetry and sediment thickness, thirty minute grided sound speed profiles and a variety of wind speed sources including historical, near real-time and simulations. For the bottom scattering, measured bottom roughness (Fox & Hays Rev. Geophys. 23(1985)) is used. Several scattering functions have been studied: the composite model (Backman (JASA 54(1973)), Berman, et. al. (JASA 88(1990), and the recent “full spectrum” formalism (Dashen, et. al. JASA 88(1990)). The Rayleigh method, described by Berman, is currently being used, due to application to both surface and bottom. Model runs are compared to low frequency bistatic reverberation data.