Multibeam radar altimetry - Spaceborne feasibility

An analysis of the inherent height and spatial resolution of an off-nadir radar altimeter is presented. For the general case, mean-square height uncertainty is shown to be proportional to the cross-track beamwidth divided by the along-track beamwidth. Thus, the cross-track beamwidth should be minimized and the along-track beamwidth maximized, subject to resolution and other constraints. A pure multibeam system with a 50-km beam offset, an altitude of 800 km, a 13.5-GHz frequency, and a 4.5-m-diameter antenna is found to yield a height random error of less than 5 cm. For the same conditions, errors decrease with increasing frequency; however, rain attenuation becomes a factor.