Forward scatter and signal coherence in shallow water

Abstract

In shallow water it is difficult to separate the effects of propagation in a waveguide composed of layered media from those of scattering produced by roughness at the layer interfaces. Moreover, to properly account for these combined effects, three-dimensional, fully elastic propagation and scattering models must be used, if a fundamental understanding of shallow water propagation is to be attained. Very few forward propagation studies include scattering effects on forward propagating signal properties such as amplitude and coherence. In shallow water such effects are critical to the condition of the signal when it reaches a target and when it returns to the monostatic receiver. The importance of these effects on the signal properties is magnified for bistatic receivers. Boundary scatter, including out-of-plane scatter, in shallow water significantly affects time and angle (as well as frequency) spreads that lead to degradation of signal coherence. The requirements to deal with scattering in three dimensions and to include full wave field physics in propagation models introduce the need for extensive computer code and computational power. While there are no simple solutions to the problems these requirements impose, the advance of computational technologies and the development of advanced propagation and scattering codes will allow comprehensive and innovative approachs. These issues are addressed and an approach to solving this significant part of the shallow water acoustics problem is discussed.