ACOUSTIC TOMOGRAPHY OF OCEAN CURRENTS BY THE MATCHED NONRECIPROCITY METHOD

The paper generalizes the matched field method to the flowing-medium c ase with special reference to acoustic tomography of ocean currents. I t is shown that by matching the nonreciprocities of acoustic fields pr opagating toward one another in opposite directions (rather than the f ields themselves), it is possible to separate the relatively weak effe cts due to currents from the acoustic signal variations brought about by variations in the sound velocity field and to determine the paramet ers of the current under study. Extensive numerical experiments on rea listic models close to the hydrological conditions existing in the Gul f Stream (the deep ocean case) and in the Straits of Florida (the shal low sea case) provide insight into the inversion stability related to emitter-receiver positioning errors, uncertainties in knowledge of the sound velocity field in the medium, specification of input variables at a limited number of points, and acoustic noise. Several alternative choices are considered for the physical quantities whose nonreciproci ty is to be matched. It is further demonstrated that recourse to the f ield phase nonreciprocity assures a highly accurate solution and a sta bility toward the errors listed above, sufficient for the proposed sch eme to be implemented in full-scale experiments.