Modeling of Mid-Frequency Reverberation in Very Shallow Water

Abstract

LONG-TERM GOALSThe long-term goal of this research is development of computationally efficient physics-based methods for modeling of propagation, scattering, and reverberation in shallow waters with complicated spatial and temporal variability of environmental parameters. OBJECTIVESA specific objective of this research is to develop a mid-frequency shallow-water reverberation model relevant to specific conditions (1 -10 kHz, ~20 m water depth, ~ 5 km range) of the ONR Target and Reverberation experiment [1] performed during the spring of 2013 (TREX13). The research is to result in developing computer simulation codes and algorithms for the TREX13 acoustic data analysis based on environmental inputs measured concurrently with the experiment.A scientific goal of this research is to contribute to involving non-traditional modeling approaches to better understand shallow water propagation and reverberation. This would support the idea expressed in the white paper [1], that a new area of investigation for WPRM (Wave Propagation in Random Media) should be suggested, to be relevant to TREX13 conditions. Particularly, for the chosen mid frequency range and very shallow waters, joint effects of the relatively large bottom penetration and 3D variability of the sediment properties, along with related effects of propagation, 3D refraction, and scattering within the seafloor, should be taken into account. Therefore, an approach is needed that treats heterogeneous stratified sediments as a critical part of the propagation channel (in addition to heterogeneous water column with rough boundaries). APPROACHThe physics of reverberation in highly heterogeneous shallow water environment can be described using an approach similar to one developed by De Wolf [2] for studying electromagnetic propagation and multiple scattering in a turbulent atmosphere. This approach is well recognized in WPRM community, and called the MFSB-approximation (Multiple-Forward-Single-Backward-scatter). Particularly, the approach is applicable to description of the so-called "backscattering enhancement" effect, known also as "weak localization" and "coherent backscatter" effects. While similar terminology appears frequently in the underwater acoustics literature, such approach for conditions of