A Study of Ocean Current on High-Frequency Acoustic Propagation in Coastal Water Environments

• Main Authors: Khang-Yen Leow, 廖康淵
• Other Authors: Chen-Fen Huang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/54938877672085379870

碩士 === 國立臺灣大學 === 海洋研究所 === 101 === A ray-tracing program for a moving medium (Current Ray-Tracing program) is developed to study the effects of ocean current on high-frequency acoustic propagation. A higher-order Runge-Kutta integration algorithm with adjustable step size is implemented for high accuracy. Numerical simulations for the waveguide of constant current velocity or constant current shear agree well with the analytic solutions. For the case of constant current velocity, the average along-ray speed perturbation is the dominant factor in perturbed travel time. The angular variation of perturbed travel time is due to the perturbed ray length. The magnitude of all perturbed ray properties are very small. For the case of constant current shear, the range variation of vertical component of wavefront normal is inversely proportional to current shear and has less dependence of the wavefront normal angle. The gradual rays are more sensitive to the current shear. For the range-dependent waveguide of deterministic small-scale bathymetric structure, Monte Carlo simulations show that the small bottom slopes have a dramatic effect on ray paths: larger predictive uncertainty is observed for steeper rays or for the case of larger current magnitude. Modeling error of effective sound speed approaches on predicting travel time comes from errors in both ray length and average along-ray speed. When using the ESSP approach (projected current on the sound speed) the dominant error is the ray length prediction. The importance of correct inclusion of ocean current in the ray-tracing program for long-range acoustic propagation is shown using a realistic ocean environment with deterministic irregular bottom topography.