Maximum a posteriori refractivity estimation from radar clutter using a Markov model for microwave propagation

This paper addresses the problem of estimating range-varying parameters of the height-dependent index of refraction over the sea surface in order to predict ducted microwave propagation loss. Refractivity estimation is performed using a Markov model for microwave radar clutter returns from the sea surface. Specifically, the parabolic approximation for numerical solution of the wave equation is used to formulate the problem within a non-linear recursive Bayesian state estimation framework. Solution for the maximum a posteriori (MAP) sequence of range-varying refractivity parameters, given log-amplitude clutter versus range data, is achieved using a technique based on the Viterbi algorithm. Simulation and real data results based on experiments performed off Wallops Island, Virginia are presented which quantify the technique´s ability to predict propagation loss at 3 GHz