Calculation of ship source level in shallow water by propagation modelling

The impact of the man-made noise on marine life is a very active area of research. Shipping noise is potentially a major contributor to ocean environmental noise due to ever increasing commercial ship traffic. For assessment of environmental impact, it is necessary to have a measure of the acoustic output of commercial ships, both to understand the noise radiated by individual ships, and as an input to the creation of a noise map of the sound field generated in by ship traffic in the vicinity of a region of interest. It is important that accurate ship source levels should be determined for an accurate noise mapping to be undertaken. The most direct way to determine the source level of a ship is to measure it under specified conditions, and work is underway in ISO TC43 SC3 to prescribe the appropriate methodology. In order to determine the source level from shallow water measurements, propagation models must be used to convert the pressure levels measured by hydrophones to the monopole source level. In this paper, a comparison of propagation modelling results for a measurement setup in shallow water is described, and some sources of uncertainty are identified.