A full field approach to acoustic tomography of oceanic currents

Abstract

Traditionally it is nonreciprocity in travel times along identified pairs of spatially close eigenrays that serves as input data for a current’s velocity inversion. In shallow water many of the rays are bottom‐interacting and cannot be resolved or identified. Hence the traditional approach results in a very poor or nonexistent resolution in the vertical plane [D. S. Ko et al., J. Geophys. Res. 94, 6197–6211 (1989)]. To avoid these problems it is suggested that one match nonreciprocity of acoustic continuous waves measured at a set of points, e.g., at a vertical array. Analytic studies indicate that nonreciprocity of the phase of a cw signal is sensitive to the flow velocity but does not depend, to first order, on fluctuations in sound speed or on uncertainties in transceiver location and, therefore, can be used as input data for currents inversion. Respective matched‐phase nonreciprocity tomography (MPNT) is simulated numerically, including effects of acoustic SNR, systematic and random environmental mismatches, number of transceivers in the array, uncertainty in their positions, etc. and compared to other possible inversion schemes. It is concluded that MPNT could be a practical tool for monitoring ocean dynamics in shallow water. [Work supported by NRC and RBRF.]