Passive Localization Using Time Differences of Eigenray Arrivals

Abstract

A localization method is developed using time differences of eigenray arrivals in a two-dimensional range-dependent underwater multiple reflection environment. This fast and robust method applies a perturbation theory to a horizontal range and a travel time which are the ray solutions given as a functional of both horizontal slowness and the sound speed profile. The linearized equations for estimating the horizontal range and depth of an unknown sound source are derived in a Cartesian coordinate system. The method’s only constraint is the applicability of the ray theory. That implies that a low-frequency sound in a shallow water environment is no more applicable than a high-frequency sound to the method because it violates the ray approximation. Identification of three eigenrays provides the passive range and depth estimation of underwater sources without a priori information on sub-bottom properties. Experiments with an impulsive source were conducted at coastal areas in Suruga Bay, Japan, to validate the patented method. The bathymetry gradually deepens toward the location of the receiver around1 km from the source. Four arrivals were detected by the use of the Wigner distribution and identified as the corresponding eigenrays. The estimated range and depth of the source are in an excellent agreement with the measurements.