Improved algorithms of ray tracings in stratified ocean

Ray model is one of the conventional sound propagation models in the water,but the inter-active effect of ocean surface and bottom on ray model will make the computation very complicated.For stratified ocean with plane bottom,sea can be expanded upward and downward to keep the sound-speed profile symmetrical,and the virtual ray traces are computed under this ideal environment,then the virtual ray traces out of the sea depth are transformed into the true ray traces within the sea depth according to some rules.This method improves the computational efficiency with the same result as before.