Statistics of monopulse measurements of Rayleigh targets in the presence of specular and diffuse multipath

In tracking of low-elevation targets with a monopulse radar, the presence of reflections from the sea surface causes 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 (pdf) of the measured amplitude of the sum signal and the amplitude-conditioned pdf of the in-phase and quadrature monopulse ratios are given for low-elevation, Rayleigh targets in the presence of sea-surface induced multipath. The means and variances of the monopulse ratios are used to illustrate the effects of diffuse multipath for a notional S-band radar.