Sound Propagation from a Coastal Source to a Deep Ocean Receiver

摘要

An experiment was performed to investigate the coupling of surface ship noise to the deep ocean sound channel. These calibrated measurements of sound propagation from the 18 m, 135 Hz source were obtained at a deep ocean receiver while the source tow proceeded from deep water up the Sable Island Bank at ranges between 730 and 910 km. The sound propagation path was from the edge of the Sargasso Sea, through the Gulf Stream and into the cold slope waters over the bank. The mean value of the transmission loss was 110 dB with a slope enhancement estimated to be 4 dB resulting from the combined effects of trapping in the strong shallow sound channel reflections from the slope. Comparisons with PE calculated results were good and indicated a strong coupling to the deep ocean sound channel. The acoustic field, sampled by 16 transverse hydrophones over six consecutive (12.5 sec, .08 Hz) samples, yielded a standard deviation of 1.7 dB (6 < or = s/n < or = 20 dB), consistent with theoretical expectations of a well-behaved multipath field. Coherent summation of slope-reflected and deep-refracted hydrophone signals yielded estimated mean values of the spatial coherence of 0.89 and a spatial coherence length of 460 meters, when multipath effects were not dominant; however, these estimates were found to range as low as 0.63 and 150 meters. These results will facilitate interpretation of the spatial coherence of the ship-induced 'slope-enhanced' contribution to deep ocean noise.