A novel bearing estimation method for shallow water targets

Aiming at solving the problem of biased bearing estimation of shallow water targets under plane-wave assumption, a novel bearing estimation method for shallow water target localization is proposed. The method adopts the normal modes sound wave theory which can truly reflect the phenomenon of numerous reflections from the bottom and great losses of acoustic energy accompanying sound propagation. The sound pressure at observation point is regarded as the superposition of some normal modes. Under the condition of flat solid seabed and white Gaussian noise, the received signal equation in matrix form is constructed for uniform linear array. The maximum likelihood bearing estimation is given as the solution of the equation by detailed mathematical derivation. Compared with classical matched field techniques, the proposed method is concise and costs much less in computational complexity. Compared with plane-wave subspace methods, the proposed method has less estimation bias. Simulation results show that while the bias of the plane-wave MUSIC grows linearly with the increase of incident angle relative to array normal, the bias of the proposed method doesn't grow evidently and that while the bias of the plane-wave MUSIC doesn't decrease too much and maintains about 27deg; with the increase of signal-to-noise ratio(SNR), the bias of the proposed method is quite small and approaches 0. Lake experiments validated the capability of the proposed method of reaching asymptotically unbiased bearing estimates of shallow water targets.