Measurement and modeling of downslope effects on long-range propagation

Ocean Acoustic Tomography (OAT) utilizes the sound speed structure of the deep ocean to permit the efficient propagation of low-frequency sound to very long ranges. The measurement of travel time on basin-scales is being used to estimate temperature variations in the North Pacific. In order to eliminate the need for accurate source location systems for long-term experiments, the source for the NPAL (North Pacific Acoustic Laboratory) experiment was moored near the sound channel axis off the Island of Kauai. The received signals at the NPAL site off the coast of Monterey California arrived on the order of 1 s late. Propagation modeling, and a measurement of the sound just off the coast of Hawaii show that at least 0.5 s delay in propagation down the slope occurs because of interaction with the sea floor.