Direction-of-arrival estimation for far-field acoustic signal in presence of near-field interferences

The far-field acoustic signal received by an acoustic array is frequently affected by near-field interferences. This causes deterioration of the direction-of-arrival (DOA) estimate for the far-field signal. To enhance the DOA estimate, the novel near-field/far-field (NFFF) beamformer is proposed. Such a beamformer optimises the beam pattern for far-field detection by maximising the beamformer output in the direction of the far-field target signal with the imposed condition to eliminate interfering signals from near-field locations. As the interference suppression only occurs at specific positions of near-field interferences, a blind zone in the far-field direction present in conventional methods will not be introduced. The NFFF beamformer is also applicable for coherent signals and for multi-interferers. For a stationary situation where interferers´ locations are fixed, the NFFF beamformer computations do not require time updates and the computational load is similar to that of the conventional beamformer. The method can be extended to several situations such as acoustic monitoring performed from a stationary platform subjected to water currents, waves, winds and other variables, all of them generating nearby interferences, and also to different array configurations including two-dimensional (2D) and 3D arrays.