A robust and computationally efficient AML method for bearing estimation in shallow water

In shallow water the plane-wave assumption on arriving signals generally leads to biased estimates of direction of arrival (DOA) of signals duo to the multi-mode propagation of sound wave, and the DOA estimation is much sensitive to the channel model mismatch and different working environments. To solve these problems, a less structured array data model based on normal mode sound field is brought forth and an approximate maximum likelihood (AML) DOA estimator is derived for uncorrelated narrowband signals with known waveforms arriving at a horizontal array in the presence of unknown and arbitrary spatially colored noise in the shallow water. In the proposed method, only 1-D searching procedure is needed. And it avoids the instability of DOA estimation caused by the channel-model mismatch and different working environments. The proposed method is validated by numerical simulations.