Using Smoothed Sound Speed To Reduce Chaoticity of Chaos in Ocean Acoustics

摘要

Chaos has been shown in the previous project (N00014-95-10443) to exhibit in three-dimensional (3-D) ray tracing for long-range acoustic transmissions in the ocean. It imposes a limitation on our ability to make long- range predictions. We have previously found that the sound speed fluctuations in the upper ocean might be a reason for large chaoticity. Therefore, we inferred that a smoothed sound speed field could reduce chaoticity and thus improve predictability. This hypothesis is tested and confirmed in this project. We still study the Heard-to-Ascension sound propagation, which has shown large chaoticity and extremely limited predictability, in our previous work, when NODC measured sound speed data were used. In this work, the same NODC data were smoothed by using a sound speed model, so that the sound speed fluctuations in both longitude direction and depth direction are ignored. We use the smoothed sound speed to perform 3-D ray tracing. Numerical results show that chaoticity was significantly reduced and consequently predictability greatly improved. The ray paths show a pattern similar to those constructed using the original NODC data. The travel times, however, were less than the previous results by about 10 seconds, with a relative error of 0.16%. This error was produced by the smoothed sound speed.