Robust Multipath Time-Delay Estimation of Broadband Source Using a Vertical Line Array in Deep Water

A method based on delay-and-sum (DAS) of cross-correlation functions is proposed for multipath time-delay estimation of a broadband signal received by a vertical line array (VLA) in the reliable acoustic path (RAP) environment. The multipath arrivals are mainly concerned with the direct (D) and surface-reflected (SR) paths. Three types of multipath time-delays are obtained, namely, the average D-D time-delay and SR-SR time-delay between two adjacent hydrophones, and the D-SR time-delay at the first hydrophone. The proposed method has significant advantages for underwater applications. First, the D and SR arrivals are successfully separated from time-delay estimation point of view, outperforming the estimation of direction of arrival with conventional beamforming. Second, the estimations of the average D-D time-delay and SR-SR time-delay between two adjacent hydrophones occur at the diagonal line of the two-dimensional DAS outputs, facilitating the automatic detection and extraction of multipath time-delays. Third, the estimation is robust against noisy background noise due to the spatial accumulative effect. The method is applied to experimental data for explosive source at ~17 km range and 300 m depth, where it is shown that simple, stable, and fairly accurate multipath time-delay estimation can be made.