ENVIRONMENTAL INVERSION WITH AN AUTONOMOUS HYDROPHONE IN A WAVE ENERGY DEVICE DEPLOYMENT SITE

Abstract: This paper presents environmental inversion results of acoustic data in shallow water in Peniche (Portugal), collected in September 2013, during the Simple Underwater Renewable Generation of Electricity (SURGE) Project- a FP7 European collaborative demonstration project aiming at building a grid connected wave energy converter of type WaveRoller. A single autonomous hydrophone was moored at the position foreseen for the Waveroller deployment. Computer generated acoustic signals were transmitted over a 3 km oceanic transect with a step of 300 m. Incoherent transmission loss (TL) for 1/3 octave frequencies in the band from 318 to 1270 Hz is used in an acoustic inversion procedure for the estimation of geoacoustic parameters of a two-layer seafloor. The acoustic inversion is posed as an optimisation problem aiming at minimising the root mean square error (RMSE) between field TL and replica TL, using a genetic algorithm. This procedure is repeated a number of times in order obtain a posterior distributions for each unknown parameter, and the solution of the inversion is obtained by taking the maximum of the a posteriori distribution of each unknown parameter. The RMSE between the field TL and acoustic model TL obtained for the solution across the acoustic transect varies between 1.5 and 2.6 dB