Source track localization via multipath correlation matching

A method for determining the track of a source emitting continuous broadband acoustic energy in an oceanic waveguide is presented. The method involves cross correlating the measured signals at horizontally separated receivers over a period of time and identifying the traces on the resulting correlogram in terms of the ray paths at each receiver that produce them. Range and bearing information is contained in the structure of the multipath correlation traces. Environmental parameters are used as inputs to a ray model to obtain the ray travel times t̄ as functions of range R. The t̄j(R) functions for the ray multipaths are used to obtain simulated correlogram time delays given a source track and receiver geometry. Constant-velocity, constant-depth source tracks are parametrized by four variables, and a nonlinear optimization algorithm is used to find the track that provides the best fit between measured and simulated correlation traces. The method is applied to measurements of a passing surface ship in the shallow waters of the English Channel. Successful localization is obtained using 4-min intervals and correlation traces produced by rays with 3–15 traversals of the water column. Receiver separation, unknown because of experimental uncertainties, is also obtained.