Effect of acoustic waves' phase speed on preciseness of DOA estimation in shallow water

The conventional beamformer is usually used to process signals received by the hydrophone arrays in direction of arrival (DOA) estimation. The reference sound speed in the beamformer plays an important role, especially at low frequency over a few hundred hertz. Errors in DOA estimation due to improper reference sound speed are analyzed in the following theoretical and numerical study. It is also indicated that the reference sound speed should be the phase velocity, which changes with the frequency evidently at low frequency. Finally, one kind of matched field method is introduced to improve the preciseness of DOA estimations with long hydrophone arrays at low frequency.