Dual-satellite crossovers

When two satellites fly simultaneously, crossovers height differences between the two satellites are available. In case of ERS-1 and TOPEX/Poseidon this provides the possibility to improve the ERS-1 orbits by minimising the crossover height differences between ERS-1 and TOPEX/Poseidon during the orbit determination process. It is a valid assumption in this procedure, that the major part of the discrepancy is due to ERS-1 orbit errors, since TOPEX/Poseidon orbit errors, and the ocean variability are of a significantly smaller magnitude.

A disadvantage of using dual-satellite crossovers in the orbit determination is that, in addition to the usually estimated parameters, also an altimeter height bias and time tag bias between two altimeters have to be estimated. Moreover, both data sets have to be converted to the same reference.