Time-domain analysis of propagation codes over megameter ranges

Abstract

From 1983–1989, tomographic experiments were conducted over megameter ranges in the northeast Pacific Ocean. Because the arrival time of acoustic pulses is dependent upon oceanic thermal structure, the data can be used to map changes in the heat content of the basin over time. These changes can be determined accurately only if the paths along which the energy travels can be identified; the errors in the propagation model must be known. In order to assess arrival time errors over megameter ranges, three codes are compared: the Kraken normal-mode (NM) program, the Navy standard parabolic equation (PE) model, and the MPP ray code. The analysis is first done in simple range-independent environments in which the normal-mode solution is theoretically exact in the far field. The arrival sequences of all three codes are compared for center frequencies of 50, 100, and 200 Hz and ranges of 1, 2, 3, and 4 Mm. The arrival patterns of a coupled NM-PE model and the MPP ray code are then compared to experimental data in a range-dependent environment.