Modeling Low-Frequency Anthropogenic Noise in the Oceans: A Comparison of Propagation Models

Increased human activities in the marine environment in recent years have caused a significant general increase in ocean noise level, raising concerns over its impact on marine life. Anthropogenic noise in the oceans covers a wide range of frequencies down to 10 Hz and can propagate over distances up to several tens of kilometers. Many environmental factors affect the propagation conditions and make it impossible to express the propagation with a simple equation. Mathematical/numerical modeling is required to predict and evaluate the impact of man-made noise on marine life. The study compares transmission loss versus range calculated by a wavenumber integration model, a model based on the parabolic equation (PE), and a ray-tracing model. The models are tested and compared for a number of different scenarios with fluid and elastic bottom layers in range-dependent environments. Each case is analyzed and interpreted at several frequencies from 15 to 250 Hz. The simulation results showed excellent agreement between the PE and the ray result for the transmission loss over a range of 10 km in a relative steep upslope elastic bottom environment and for frequencies down to about 25 Hz. In another test, comparisons over a 50-km upslope continental shelf scenario resulted in good agreement for the fluid bottom for frequencies above 100 Hz and poorer for 50 Hz. Over the elastic high loss boom, the two results showed the same general trend but with differences in details. Overall, the ray-tracing model appears to be an acceptable and efficient choice providing reliable predictions, even at low frequencies, in shallow water