Is received level average sufficient to describe ambient noise in heavy traffic areas

The Marine Strategy Framework Directive imposes to European governments to monitor ambient noise. There are multiple ways of monitoring the ambient noise. Although certainly economical considerations have to be taken into considerations, there is a need to discuss the representativeness of ambient noise measurement by the only means of hydrophones. A hydrophone will only give a local and punctual knowledge. As long as the measurement is not contaminated with self-noise, mechanical noise from the mooring itself or the water flow around the sensor, measurement present the great advantage of providing a ground truth. However, for ambient noise being stochastic by essence, masking effects between numbers of anthropic sources are likely to occur for significant period of times. Hydrophones therefore measure the closest noise events. An ambient noise experiment done in the western part of the British Channel in 2010 has demonstrated such effects, and serves questioning the representativeness of noise monitoring exclusively based on measurement. The choice of the metric and the influence of the geographical configuration of the monitoring scheme on noise characterization will be discussed. Coupling measurement with modeling is foreseen as a solution to bring more representativeness to ocean noise assessment.