Passive source localization with a horizontal line array in the shadow zone of the deep water

Passive source localization remains a prominent research focus in underwater acoustics. Although extensive studies in deep water have emphasized localization using vertical line arrays, far less attention has been directed toward utilizing horizontal line arrays (HLAs) for estimating source range and depth, despite their widespread deployment in deep-water operations. This paper presents a broadband source localization method employing an HLA in the shadow zone of deep water. The proposed approach estimates source range and depth by matching six measured time delays among four dominant multipath arrivals against a precomputed replica library of modeled time delays generated across a grid of hypothesized source ranges and depths. The time delays are extracted from the beamformed acoustic intensity steered toward the estimated source direction. Method effectiveness is validated through both numerical simulations and experimental data acquired during an experiment in the South China Sea, involving a suspended broadband source and a towed HLA. In comparison with the matched-interference-structure method, the proposed technique significantly reduces computational complexity while demonstrating enhanced robustness against environmental mismatches such as sound speed profile and water depth uncertainties.