Range-dependent 3D scattering and reverberation in the continental shelf environment from biology, geology and oceanography

Abstract

Several unified scattering and reverberation models were developed in support of the ONR Acoustic Clutter Program. They include a range-dependent model based on the parabolic equation that can be used to efficiently model scattering from a random spatial distribution of random targets that obey the sonar equation in the waveguide and a similar but range-independent waveguide model based on normal modes for scattering from extended objects. Both these models are bistatic and fully 3D, and the latter model also accounts for modal coupling between propagation and scattering caused by extended objects in the waveguide. These models are applied to examine both coherent and diffuse scattering measured after beamforming and match-filtering on an array from schools of fish, plankton, volume inhomogeneities in the sea bottom, roughness on the seafloor, extended seafloor and sub-bottom features such as river channels and reflective strata, and internal and surface waves. We provide a review of the dominant sources of clutter as well as background reverberation for long range active sonar based on comparison of model predictions with measured data from the Acoustic Clutter Experiments of 2001 and 2003.

Remote Sensing in Fluctuating Range-Dependent Littoral Environments with Clutter

“…Extensive modelling of transmission loss [3] and sea bottom reverberation [3,4,6] in the highly range-dependent environment of Georges Bank were conducted prior to and and during the experiment using the parabolic equation approach. During the experiment, the daily XBT and CTD measurements were used to derive the sound speed profile in the water column and used as inputs in the numerical models.…”

“…A theoretical and numerical model for reverberation due to volume inhomogeneities in the sea bottom based on Green's theorem is currently under development. [3,4,5,6] The expected reverberation intensity in this model depends on the statistical moments of the fractional changes in compressibility and density, which scatter like monopoles and dipoles respectively, and the coherence volume of the inhomogeneities. The model is being calibrated using data acquired with a long range sonar on the New Jersey continental shelf during the 2001 and 2003 acoustic experiments of the ONR Geoclutter Program.…”