Satellite altimeter calibration techniques

Abstract

During the next five years several satellites carrying high accuracy radar altimeters are scheduled for launch. These include the European Space Agency ERS-1 satellite and the jointly sponsored NASA/CNES TOPEX/POSEIDON satellite. In-flight height calibration and height stability verification for both satellites are planned, and studies have been conducted to ascertain the calibration techniques which can most effectively satisfy the mission requirements. All of the proposed calibration techniques require at least one laser to provide the satellite height reference. For most techniques, only one laser in the calibration area is utilized; in this instance the satellite groundtrack must pass relatively close (within 20 km) to the laser site in order to obtain an orbit height uncertainty of less than one cm. The currently proposed calibration techniques for over-water calibration include: (1) tide gauge on a tower at-sea and a nearby laser; (2) laser and tide gauge on an island with offshore satellite pass and geoid tie between satellite groundtrack and laser, (3) tide gauge on a tower at-sea with satellite positioning from multiple lasers and a Global Positioning System (GPS) tie between the lasers and tide gauge; and (4) laser and tide gauge on a tower at-sea. Error budgets for these techniques have been developed based on state-of-the art laser tracking systems. For a single pass, these budgets have been found to have one sigma height uncertainties in the 2.8 to 4.9 cm range.