Angle measurement with a phase monopulse radar altimeter

It is possible to enhance the conventional satellite radar altimeter in such a way that the range measurement is accompanied by an angle measurement. This is useful if the applications of these altimeters are to be expanded to include nonlevel surfaces such as continental ice sheets and land. The angle measurement can be made in one or two directions through the inclusion of one or two additional antennas and receiver channels and the integration of complex "cross-channel" waveforms whose phase indicates the angle to the point of first reflection from the scattering surface. This paper develops the measurement concept and establishes the precision of the resulting elevation measurement through an analysis of the dominant sources of error within the Instrument. It is shown through analysis and numerical simulation that elevation errors over a flat tilted diffusely scattering surface can be maintained below the l-cm level. The impact of antenna pointing and surface roughness are considered.