Absolute and Relative Calibration of Ers-2 with Applications to Envisat

Continuous monitoring of the range stability is a pre-requisite for sea-level rise and other demanding applications in satellite altimetry. Range stability may be investigated by either absolute or relative calibration techniques. In this study relative calibration is undertaken through intercomparison against TOPEX/Poseidon and absolute calibration undertaken in the vicinity of 8 tide gauges around the UK. In the former, dual crossover residuals between ERS-2 and TOPEX/Poseidon are analysed for the relative bias along with other spatial and geophysical parameters. The relative bias is subsequently corrected for the observed TOPEX drift as deduced by comparison against the global network of tide gauges. This procedure provides a better estimate of the relative bias than achieved by using the global tide gauge data set, as for TOPEX/Poseidon. In the absolute calibration approach, tide gauge measurements are extrapolated to the sub-satellite points using local models for ocean tides and the geoid; each of the tide gauges having been tied geocentrically to the satellite frame by episodic GPS measurement.