Several groups have considered the requirements for such a data set, and a consensus assessment is that many critical studies would be enabled by the availability of a digital global topographic model wich accuracies of 2 and 30 m in the vertical and horizontal directions, respectively. A radar interferometer is formed by combining the radar echoes received at a pair of antennas displaced across-track, and specialized data processing results in the elevation data. The former requires an interferometer baseline length of about 15 m to achieve the required accuracy, and thus could be built on a single spacecraft with a long extendable boom. The latter necessitates a kilometers-long baseline, and would thus be best implemented using two spacecraft flying in formation. For the dual-spacecraft systems, though, differential global positioning satellite measurements possess sufficient accuracy.
Studies indicate that similar performance can be realized with either system.
Howard A. Zebker, Thomas G. Farr, and Ronald P. Salazar of the Jet Propulsion Laboratory, California Institute of Technology.