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Normal-mode based music for bearing estimation in shallow water

In shallow water, the plane-wave direction-of-arrival (DOA) estimators generally yield biased estimates, due to the multimode nature of acoustic propagation. To solve this problem, a normal mode array model is described. And a Normal-Mode based MUSIC method, referred as NM-MUSIC, is proposed for DOA estimation, which is adapted from the classical MUSIC method. The present NM-MUSIC method obtains unbiased DOA estimates by angle searching in the given multi-dimensional functions of the horizontal wave number steering vectors of normal modes. Numerical results show that the NM-MUSIC method could effectively eliminate the bias of DOA estimates caused by multimode acoustic propagation and reach asymptotically unbiased DOA estimates of sources located in shallow water as SNR increase.