Acoustic sensing of temperature changes in a strongly range-dependent ocean

The inverse problem of inferring information about the intervening ocean ca n be solved by a comparison of the computed arrival times and measured patt erns of arrivals. This approach is Very effective if in the process of soun d signal propagation the modal energy exchange is negligible, the mode prop agation can be considered as adiabatic and each mode has a clear amplitude and phase. In the range-dependent ocean, drastic 'repopulation' of the mode s takes place due to intense energy exchange. The energy distribution betwe en modes changes, and the order of modal arrivals varies. For the strong-mo de-coupling case a fixed mode travel time does not have a monotonic relatio nship with the temperature variation. To obtain monotonic dependence of the sound signal parameters upon the environmental characteristics, specific a pproaches to the forward problem solution have to be used; two of them-the collective arrival time and the cumulative sum-are considered in this paper . They consists of defining trends in the signal arrival pattern caused by the temperature changes, and computing average parameters of the arriving s ignal ensemble.