Abstract:
A method for characterizing a range-dependent acoustic waveguide by remote sensing is examined. The approach is to transmit from a limited number of source locations and measure the propagating field along a vertical array. Characterization of the environment is cast as an inverse problem where the goal is to determine the mode coupling coefficients from the acoustical measurements. Ideally, measurements from the source at a single location should suffice to characterize the medium when the propagation is adiabatic. When there is coupling, the problem is underdetermined and unstable if the number of source locations is less than the number of propagating modes. Tikhonov regularization is used to build stability into the inversion algorithm. The number of measurements required is shown to be directly related to the nature and extent of the mode coupling. The method is demonstrated by numerical simulation for two shallow water scenarios: a sloping bottom and a randomly rough bottom. [Work supported by ONR.]