Characterisation and subtraction of current flow noise in hydrophone recordings

In the interior of the Ría de Arousa, on the northwest coast of Spain, a hydrophone is installed to provide information on environmental noise, which is very high due to the intense traffic in the area. The hydrophone, together with various oceanographic and meteorological observation equipment, is installed on a floating platform anchored in a very shallow water area with strong tidal currents. These currents cause flow noise that affects the estimation of the noise descriptors established by the Marine Strategy Framework Directive. The aim of this work is to characterise the current flow noise at the hydrophone in relation to the instantaneous current measured simultaneously at the same location. From this characterisation, the current noise spectrum is defined and subtracted from the recordings prior to the calculation of noise descriptors. This contribution provides details of the analysis of the hydrophone signals, the calculation of the flow noise spectrum as a function of current, the spectral subtraction procedure used and the effect of the subtraction on the calculation of the noise descriptors.