The effects of seamount on sound propagation in the negative gradient sound speed environment

Based on the experiment data collected in the South China Sea in 2015,the effects of seamounts on sound propagation with negative gradient sound speed profiles are studied.Reasonable interpretations are given for the observed anomalies in Transmission Losses (TLs) in terms of acoustic ray propagation,demonstrating that the existence of a seamount in propagation direction leads to the fluctuations of TLs with respect to range.When the source is near the Vertical Line Array (VLA) at 7.6 km,rightly on the slope of the seamount,8 dB decease of TLs is observed for the slope reflection,confirming a similar mechanism of enhancement of down-slope in SOFAR channel waveguide.When sources are launched over the seamount,the seamount shadowing leads to more than 20 dB increase of TLs at 23.8 km and fluctuations at specific spots for differences of acoustic shadowing.Furthermore,quantitative numerical simulations based on the experiment environment are also performed by the parabolic equation model.The simulated TLs at several receiving depths show good accordance with the experiment data,which verifies the effects of reflection and shadowing of the seamount.In addition,the analyses of acoustic shadowing losses at different source positions reveal a linear relationship between shadowing losses and the logarithm of frequencies at specific frequency band.