Statistics of monopulse measurements for tracking targets in the presence of sea-surface induced multipath

In tracking of low elevation targets with a monopulse radar, the presence of reflections from the sea surface can cause severe errors in the Direction-Of-Arrival (DOA) measurements of the target. Since the target echoes that are received directly and via the sea surface are unresolved in time and frequency, tracking targets in the presence of sea-surface induced multipath is a special case of tracking unresolved targets. The sea-surface reflection is modeled by a specular (coherent) component and a diffuse (noncoherent) component. The probability density function of the measured amplitude of the sum signal and the amplitude-conditioned means and variances of the in-phase and quadrature monopulse ratios are given for low elevation targets in the presence of sea-surface induced multipath. The means and variances of the monopulse ratios are studied for radars operating at S, X, and Ku bands.