Passive synthetic aperture array to improve noise mapping of a moving ship

This paper addresses the issue of estimating underwater noise mapping of a moving ship using a static linear hydrophone array. In the context of pass-by experiments, moving-source mapping is classically performed using an extension of conventional beamforming to moving sources: beamforming-MS. The main issue of moving-source mapping using beamforming-MS is the poor spatial resolution of two close sources in a noise map at low frequencies. To improve the spatial resolution of beamforming-MS, a passive synthetic array is built in the time domain as a pre-processing of the beamforming-MS, using the a-priori knowledge of the trajectory of the mapped vehicle. The short time synchronization strategy of the extended towed-array processing method ( [1]) is proposed in order to be robust to nonstationary propagation conditions. The efficiency of this strategy is validated using an aerial experiment with two loudspeakers in a semi-anechoic chamber, and an underwater experiment with a towed-ship model in a mountain lake. Two criteria are suggested to objectively and experimentally assessed the quality of the construction of the passive synthetic array.