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.

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Underwater platforms provide long-term detection of undersea targets. In this paper, we propose a method for the estimation of target motion parameters by submerged static acoustic detection equipment. The proposed method is based on the Radon transform of modeling the target moving in a uniform straight line. The heading angle, the time to the closest point of approach (CPA), and the ratio of velocity to the horizontal range of the target at the CPA to the sensor are obtained by applying the generalized Radon transform (GRT) to bearing–time records. The velocity of the target is determined by applying the GRT to the line-spectrum–time records. Furthermore, the motion trajectory of the target with respect to the detection equipment can be calculated from the above parameters. To validate the feasibility and performance of the proposed method, computer simulations and sea trials based on a fixed single vector measurement system were analyzed in this paper. The results suggest that the proposed method can accurately estimate the motion parameters and can calculate the trajectory of the moving vessel along a straight line at constant velocity.

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