Underwater three-hydrophone array passive ranging using time-dimensional Capon beamforming

The three-hydrophone array is often used for underwater passive ranging. It uses the time delay estimation (TDE) between hydrophone pairs to calculate the target range. Traditionally, the generalized cross correlation (GCC) algorithm is used for TDE. However, when the available bandwidth is limited, the accuracy of GCC decreases severely and thus, fails to meet the performance requirement. To solve this problem, we propose a new TDE algorithm based on time-dimensional Capon beamforming. The proposed method uses Capon beamforming to process sampled signals at hydrophones to obtain the time-domain output and accordingly calculates the time delays between hydrophone pairs. Specifically, we extract several subband components from GCC outputs in the frequency domian. To suppress the amplitudes fluctuation between different subbands, the subband amplitude modification and the diagonal loading (DL) algorithm are used to improve the robustness of time-dimensional Capon beamforming. Finally, we estimate the range of target using the TDE result obtained by the proposed method. What's more, to analyze the TDE accuracy of the time-dimensional Capon beamforming, we compare the TDE variance of both GCC and the proposed method with Cramér-Rao lower bound (CRLB) under different simulation conditions. The results demonstrate that the proposed algorithm could significantly improve the performance of passive ranging in three-hydrophone array, in the case of relatively short bandwidth associated with subband amplitude fluctuations.