Resolving travel-time variability of the coupled oceanographic-tomographic analysis and prediction system (COTAPS)

Abstract

It has been suggested that the tomographic approach that feeds the 8–11 kHz ocean acoustic measurements into an ocean model using data from bottom-mounted hydrophones, suffers from a significant travel-time variability due to the surface waves. In this work, the influence of the ocean surface motion on the acoustic travel times has been studied using both the experimental data collected at the Pacific missile range facility (PMRF) off Kauai, and an appropriate acoustic model. The ray-based acoustic model developed is an adaptation of the range-dependent version of Bellhop with the modified top surface characterizing ocean surface waves. The model-generated time series suggests a direct relationship between the phase of the top surface wave and the time-of arrival, which is further confirmed by the experimental data. Furthermore, an approach is developed that automatically decouples the effect of the top surface waves from the environment-related phenomena, making it possible to assign the travel time variations produced by the physical phenomena independently of the surface geometry, in turn eliminating the surface related error. [Work supported by the ONR.]