Penetration of sound into the cold eddy of the Sargasso Sea

Abstract

The results of an acoustic experiment performed in the Sargasso Sea are analyzed. The position of the receiving vessel was in a cold eddy. A 120-km-long acoustic path began in the warm waters of the Sargasso Sea and ended at the receiving vessel. Broadband sound signals were produced by 2.8-kg charges, which were fired at a depth of 290 m by another vessel moving at full speed. The interval between the explosions was 2.5 km. The signals were received by three independent hydrophones positioned at depths of 220, 600, and 1200 m. In processing the experimental data, the main attention was paid to the variability of the parameters of signals belonging to signal quartets with different numbers of bottom reflections. For these signals, on some segments of the path, a considerable intensity decrease (reaching 12 dB at frequencies above 200 Hz) was observed. For signals with different numbers of bottom reflections, the interval of distances corresponding to the intensity decrease was found to be determined by the same range of signal launch angles. It is concluded that the phenomenon under consideration is caused by the presence of a region with high horizontal sound velocity gradients, which correspond to the transition from the cold waters of the eddy to the warm waters of the Sargasso Sea. An attempt is made to reconstruct the shape of the frontal boundary.