The effect of sea-surface roughness on shallow water waveguide propagation: A coherent approach

Standard propagation models in underwater acoustics (e.g., normal modes, PE) are deterministic in nature, i.e., they deal with a single realization of the environment. Additionally, for mathematical reasons, they typically treat the sea surface as a flat pressure-release surface. Effects of sea surface and bottom roughness are incorporated through a loss mechanism. This is accomplished by including an additional attenuation factor based on coherent loss of the surface-interacting component of the propagating field. This type of correction presents a mathematically inconsistent model, since usually results from stochastic scattering models are applied to results from single realizations of the stochastic medium. Moreover, scattering kernels are generally derived assuming a homogeneous medium underlying the sea surface, an assumption incompatible with a realistic environment. Using a numerical model [Norton et al., J. Acoust. Soc. Am. 97, 2173–2180 (1995)] that combines a high fidelity Parabolic Equation propagation model with the conformal mapping technique developed by Dozier [L. B. Dozier, J. Acoust. Soc. Am. 75, 1415–1432 (1984)] to handle surface roughness in a marching algorithm, forward propagation with a single realization of a rough sea surface overlying a complex ocean environment can be modeled in a mathematically consistent way. This technique is applied to the problem of shallow water propagation with a rough sea surface. For the adopted environment and range of rms roughnesses considered (0.28