Subarray adaptive beamforming for reducing the impact of flow noise on sonar performance

The performance of a hull-mounted sonar array is adversely affected by the presence of own-ship self noises such as propeller noise, machinery noise and flow noise. Among those self noises, the effect of flow noise can be very difficult to combat due to its near-field and non-stationary nature. In this paper, we investigate the effectiveness of using two stage subarray adaptive beamforming for reducing the impact of flow noise. Two subarray adaptive beamforming schemes are considered. These are adaptive-conventional and adaptive-adaptive beamforming. The performances of these two schemes are evaluated against the performance of a full array adaptive beamformer which provides a benchmark in terms of the array gain. In the study, we model the flow noise as a stream of moving quadrupoles. The investigation shows that subarray beamforming is able to achieve higher array gains than a full array adaptive beamformer. The reasons for this are analysed. It is found that the time required for full array adaptive beamforming to converge is too long in a fast time-varying environment.