A comparison of parabolic equation models with stepwise coupled modes in a shallow-water range-dependent environment

Abstract

Parabolic equation calculations are compared with stepwise coupled mode COUPLE calculations for a set of runs for which the two models have overlapping capability. The PE calculations were then extended to consider the additional case of refracting sediment. Normal mode start-up fields were used in the calculations. PE models have capabilities differing in the areas of wide angle capability, treatment of the bottom, and numerical methods. The intent of this paper is to discuss which of these differences make a difference. The environment chosen was that presented in the previous paper. Calculations were performed at 50 and 300 Hz. Water depths varied somewhat, but averaged about 150 m, corresponding to 3 wavelengths and 15 wavelengths at 50 and 300 Hz, respectively. The dependence of depth with range took two forms. The first consisted of smoothly varying linear segments, the second was the same as the first with a number of spikelike irregularities added in. Differences are discussed in terms of numerical issues and the physics incorporated in the models.