Internal waves and matched-field processing

Abstract

The performance of matched-field processing is degraded due to randomness of the propagation medium. With a vertical array, this degradation takes the form of fragmentation and wandering of the peaks (mainlobe and sidelobes) in the range-depth ambiguity surface. The resulting errors in localization are characterized in terms of the rms processor output. Simulations and theory specialized to the cw Bartlett processor are used. First, the case of an ocean waveguide with a quadratic average sound-speed profile and vertically stationary sound-speed fluctuation statistics is examined. Next, approximations are introduced so that a relatively simple analytic model can be abstracted from the theory. This model is checked against Monte Carlo PE computations that avoid some of the simplifying approximations. The simple model contains scaling rules for processor performance as a function of frequency, array length, and medium vertical correlation length. In general, the effects of internal waves become more important as frequency increases, array length increases, medium correlation length decreases, and range increases. The processor is predicted to be most sensitive to internal-wave mismatch for sources that are in convergence zones. Finally, the analytical model is compared to Monte Carlo PE computations using oceanic realizations obtained from a realistic dynamic internal wave model.