Sub-antenna processing for coherence loss in underwater direction of arrival estimation.

This paper deals with the loss of coherence in underwater direction-of-arrival estimation. The coherence loss, which typically arises from dynamical ocean fluctuations and unknown environmental parameters, may take the form of a multiplicative colored random noise applied to the measured acoustic signal. This specific multiplicative noise needs to be addressed with methodological developments. This paper proposes a weighting process that locally mitigates the effects of the coherence loss. More specially, a set of coherent sub-antennas is designed from the so-called Mutual Coherence Function (MCF). The assessed source position results from the combination of each sub-antenna by using a mixed norm. Two experiments are considered in the paper: either a random noise is sampled to simulate the effect of random ocean fluctuations, or a synthetic acoustic waveguide is used in which the coherence loss is due to some multipath interferences. It is shown that the weighting process allows for a decrease in the estimation error in comparison to a Conventional Beamformer (CB).