Towards a Standard for Vessel URN Measurement in Shallow Water - Final

Abstract

Performing repeatable vessel source level (SL) measurements is difficult in shallow water because of the way that the environment affects received sound pressure. In deep water, with a hydrophone far from the seabed, it is relatively straightforward to estimate propagation loss (PL) and convert sound pressure level (SPL) measurements into SL using methods codified in existing standards (ISO 17208 and ANSI S12.64). Estimating PL is more difficult in shallow water because of the way that sound reflects from the seabed and multiple propagation paths contribute to the received sound pressure. Obtaining repeatable SL measurements in shallow water therefore requires straightforward and robust methods to estimate PL. A field experiment, developed in consultation with an ISO working group on shallow water URN measurement, was carried out to evaluate several different methods of measuring vessel SL in shallow water. Three anonymized partner vessels were measured many times, in three different water depths and with six different hydrophone arrays. Results of the experiment confirmed that it is possible to obtain repeatable vessel SL estimates in shallow water, comparable to those obtained in deep water. Furthermore, the methods required are only moderately more complex than those codified in the existing standards.