Numerical calculation of bounds on array performance using the parabolic-equation technique

Abstract

The standard approach to the problem of determining the effects of ocean variability, i.e., internal waves, on system performance is to measure or calculate the mutual coherence function for the acoustic field since it enters directly into measures of system performance such as array gain. Because of difficulties in determining this quantity, we have taken a different approach. Rather than attempting to calculate, e.g., array gain, we seek only to bound it. Consequently, we calculate a limit on the degradation in system performance. The advantage of this approach is that the limit depends only on the mean pressure field, a quantity easier to calculate than the mutual coherence function. The calculation of the mean field does require, however, the use of a generalization of the Markov approximation appropriate when diffracting and refracting effects are present. With this approximation the calculation of the mean field can be carried out with a slightly modified version of the parabolic-equation technique of Tappert and Hardin. A case study is made for propagation in the Western North Atlantic.