Pulse response measurements over three 45‐km propagation paths in the Florida Straits

Abstract

Three point reciprocal transmission experiments, undertaken in the Florida Straits, have yielded a 35‐day time history of shallow water pulse responses for 45‐km ranges in a depth of approximately 550 m. The transmitted pulses consist of 4 cycles of a 460‐Hz carrier. Several distinct and separable arrivals persist throughout the 35‐day period for all three ranges. The sound‐speed profile has a 90‐m surface duct above a negative gradient of approximately 0.15 (1/s). Both the sound speed and bathymetry have complicated range dependence and the medium is highly variable in time owing to meanders of the core of the Florida Current. Yet, the arrival patterns are remarkably stable. The observed time spread of all arrivals is nearly a full second. Travel times of the earliest arrivals are consistent with surface duct transmission, whereas later arrivals are consistent with ray model predictions for refracted bottom reflected (RBR) rays. The RBR arrivals are spread over approximately 0.3 s. Ray models, normal mode, and PE models are used to predict and identify intermediate arrivals. [Work supported by ONR.]