The reflection and shadow effects of seamounts on sound propagation in deep water

Abstract

The seamounts have enormous effects on sound propagation in deep water. Some abnormal propagation phenomena were observed for two different tracks with the flat bottom and the seamounts bottom environments. A propagation experiment was conducted in the South China Sea in 2014. The effects of seamounts on sound propagation were analyzed by using the wideband signals. It’s observed that, in the first shadow zone about 28 km, the transmission loss (TL) for the environment with the seamounts was decreased up to 7 dB compared with the TL for the environment without the seamounts, due to the reflection effects of the seamount. And in the first convergence zone about 56 km, the TL was increased more than 30 dB for the shallow source. It was because that most of the deep refraction waves were blocked by the seamount. In the reflection zone of seamount, the TL increased as the depth of the receiver became deeper for less of sound rays could arrival and most of the grazing angles became bigger. Moreover, the TL difference between receiver depth 170 and 1868 m was nearly 10 dB. At the range more than 30 km, the TL trends were consistent as receiver depth vary from 170 to 1868 m, because it can be equivalent to that all the rays were reject from the top of the seamount. The numerical TLs and pulse arrival structures can match with experimental results well. Abnormal TLs and pulse arrival structures at different ranges are explained by using ray and wave theory.