Shallow Water Effects on Ship Underwater Noise Measurements

The underwater noise of icebreaker Polaris was measured in shallow water. The measurements were conducted using one hydrophone at the sea bottom and three hydrophones at intermediate depths. The noise measurements were analysed in this paper at port side passes at 11 knots speed. Transmission loss was investigated in shallow water for ranges typical in noise trials between the target ship and the measurement location. The transmission loss at different depths and frequencies was analysed from the measurements. The measured transmission loss was compared to the results of acoustic propagation models. The sensitivity of transmission loss to bathymetry and seabed sediment characteristics was studied numerically by systematically varying bottom geometry and its acoustic properties. The noise measurements conducted with two different methods gave relatively close results although the measurements were done in water depths not reaching the minimum levels of classification notations. The numerical simulations revealed the complicated underwater acoustic environment present in shallow waters