Variation in Cutoff Effect and Sound Field Caused by Geometrical Structures near the Coast

Abstract

The mysterious mass stranding of whales often arises in specific areas in the world. Moreover, vibrational noise, suspected to originate from large-scale construction in coastal areas, is problem. These problems could be considered to be related to sound propagation near coastal areas with a special geometrical structure and an ambient noise environment. We set up a propagation model in a coastal area, and simulated low-frequency sound propagation near the coast using the parabolic equation method (PE method) and the normal mode method. It has been shown that low-frequency sound cannot propagate from the ocean to the coast owing to the cutoff effect of shallow water that occurs when there is a water layer with a basement half space. However, when the water layer has a sediment layer, mode coupling occurs between the water layer and the sediment layer and propagation attenuation rapidly decreases. Sound can propagate to the coast in this case.