Dominant Rays Analysis in Shadow Zones of Deep Ocean and Its Application on Fast Bearing Estimation of Active Sonar

In shadow zones of deep ocean, the horizontal line array of active sonar is unable to distinguish the elevation angle and the bearing angle because of its axial symmetry, which leads to bearing estimation error when the elevation angle is large. The traditional improved method estimates elevation angles of all positions with acoustic field model and then gets the actual elevation angles according to the actual time delay for beamforming weight vector compensation, whose computing efficiency and real-time performance are low. In this paper, an improved fast bearing estimation method in shadow zones is proposed. We show that the sound field fluctuation in shadow zones is due to the energy fluctuation of the rays having different emanating angles. And a quantitative relationship between the detectable areas and the rays with high energies is calculated based on the ray interference theory. The elevation angles at the boundary location of the detectable areas can be calculated according to this relationship. And hence, elevation angles of all positions can be obtained by linear fitting. Simulation results show that this method can decrease bearing estimation errors effectively, meanwhile it has a much low computation burden which is useful for the real-time calculation.