Passive matched sound intensity localization using a deep ocean-bottom seismograph in the direct-arrival zone.

In the direct-arrival zone, the crucial preliminary step for depth estimation by matching the narrowband sound intensity is accurately estimating the elevation angle or the slant range (for calculating replica field). However, the elevation angle estimated by an ocean bottom seismograph may not be satisfactory, leading to mismatch issues for the matching processing algorithm and resulting in inaccurate range and depth estimation results. To overcome this problem, the multidimensional matched sound intensity processing (MD-MSIP) method is proposed. The MD-MSIP is defined as a joint estimation of the initial range, the target speed, the closest point of the approach range, and the source depth. By matching these four preset parameters, the target can be located, which does not require the elevation angle when calculating the replica field, avoiding the influence of the elevation angle error on MSIP. The experimental results demonstrate that the relative errors of the depth and range estimation results can be controlled within 10% and 20% by MD-MSIP, respectively. The target trajectory can also be estimated using the azimuth. In addition, the robustness of MD-MSIP is enhanced during the mismatch of the sound speed profile using the slow phase variation characteristics of the low-frequency signals.