Broadband scattering models for acoustic time-fronts in deep water

Abstract

Acoustic time-fronts that propagate in the deep ocean undergo scattering due to internal waves. Sound-speed perturbations induced by internal waves cause changes in the mean intensity of the time-front and also scatter energy into the shadow zone. This paper presents a mode-based broadband scattering model to predict the intensities of the time-front. The model uses transport theory equations that combine the physics of acoustic mode propagation and scattering due to internal waves. Complementary to this model, this paper also considers a low complexity version, which uses the adiabatic phase approximation, and thus offers savings in computations. This paper compares both the models predictions against the observations from the Philippine Sea (2010-2011) deep water experiment (PhilSea10). The comparisons show that while both the transport theory models predict the statistics of mode pulses, the low complexity version fails to predict the intensities of the time-front. The full transport theory further suggests a mode-based explanation for energy scattering into the shadow zone. This paper also presents some limitations of the transport theory in predicting the mean arrival time of mode pulses.