Low-Angle Tracking in the Presence of Ducting, Coherent and Incoherent Multipath

摘要

This report presents results on recent improvements to the low-angle trackingalgorithm based on the Refined Maximum Likelihood (RML) method. Specifically the report describes results obtained for three different models: (1) the RML model; (2) a model which accounts for radar fluctuation of the specular return; (3) a third model which accounts for the effect of ducting. The results indicate that the simple RML model produces better results than obtained by using a model that attempts to account for the incoherent fluctuation in the specular direction. In the case of ducting, under moderate sea state conditions, the parabolic approximation of the Helmholtz wave equation gives accurate tracking while a simple two-ray multipath model (Kerr) is used for standard propagation conditions. For very high sea states, phase monopulse with averaging over a number of estimates at different frequencies gives sufficient accuracy for most applications.