The Study of Estimation Method for Sound Exposure Level Taking Account to Ocean Environment and Moving of Source and Receiver

Abstract

Recently, there has been a worldwide movement toward the reduction of underwater noise from shipping. In Japan, research has been conducted on the behavioral reaction of whales when exposed to underwater noise from shipping in the sea around the Ogasawara islands. In shallow water such as that sea, sound propagation is affected by environmental parameters of the path between the sound source and receiver. Additionally the sound source and receiver both move continuously. Therefore, it is impossible to estimate an accurate SEL (sound exposure level) for the receiver with the commonly used equation of spherical spreading loss. The objective of our research is to examine the estimation method for accurate SEL, taking into account the influence on sound propagation of environmental parameters and movement of the sound source and receiver. We simulated the sound field at every two minutes within a circle area of the sea when a ship was navigating, and made a SEL map that integrated these sound fields. In addition, we compared the SEL maps based on the simulation and on the equation of spherical spreading loss. Finally, we illustrated the differences in SEL estimated by the two maps.