Oceanic low-angle monopulse radar tracking errors

Radar systems often experience difficulties when tracking low-altitude targets over the ocean because of multipath effects. Whenever the radar cannot resolve the target from its image, it will track a false target position which can move far above or below the actual position. In this paper, mathematical models are utilized to quantitatively determine the degradation in tracking ability of a monopulse radar due to multipath. The model incorporates provisions for the antenna sum and difference patterns, including sidelobes, and for the antenna polarization. Divergence factors are utilized to account for the curvature of the earth's lossy surface. More accurate calculations of the phase length of the direct and reflected rays using the spherical earth model are included. Smooth and rough surface models are used to model the prevailing sea state. The smooth surface model determines both stable and unstable equilibrium directions toward which the target position is indicated. The rough surface model defines a band of maximum error in the indicated position, as a function of the surface waveheight, and it includes both the rough specular and the rough diffuse reflection term.