Posterior distributions of a statistic of propagation loss inferred from radar sea clutter

摘要

The generation of a posteriori distribution of a statistic of propagation loss conditioned on observed radar sea clutter is described. The statistic u is the 20th percentile level of the two-way propagation loss at a 5-m height over the 10–60 km range interval. A discrete implementation of the Bayesian paradigm is employed. The forward mapping from the space of environmental parameters into the space of radar clutter incorporates a random process model such that many realizations of modeled clutter are generated for each environmental refractivity parameter combination. The algorithm is adjusted such that over a series of simulated inversion runs, it is seen that for intervals between percentile levels (e.g., between the 20th and 80th percentile levels), a posteriori distributions of u contain the ground truth values of u the correct percentage of the time (60% for the used interval). For real data cases, it is observed that the a posteriori distributions are too narrow. The inversion algorithm is used to examine the behavior of the a posteriori distribution as the noise floor is raised. An abrupt reduction in the information obtained from the clutter (indicated by a widening of the a posteriori distribution) occurs when peak clutter levels over the ranges of 25–50 km drop below about 15 dB for both simulated and real data cases.