Mean Sea Level trend estimation from multi-mission altimetry and tide gauges
Joel Dorandeu(1) , Michael Ablain(1) , Yannice Faugere(1) , and Fabien Lefevre(1)
8-10 Rue Hermès,
The Mean Sea Level (MSL) trend estimation has become an essential objective of satellite altimetry, as it is related to global climate change. However, great precision, high stability and long term series are required. So maintaining altimeter systems and data at the level of accuracy of 1 mm/year at global scale still remains a challenge.
With a 15 year time series, altimetric measurements are now widely used for MSL trend estimation. As an expert in altimetry, CLS is involved in the calibration and validation of TOPEX/Poseidon, ERS-1/2, Geosat Follow-On, Jason-1 and ENVISAT. To insure reliable Mean Sea Level estimations, precise cross-comparison between altimetry missions is necessary. Estimates from the different missions are compared and analysed according to the specificities of each altimeter system in terms of performance of instruments, orbit or geophysical corrections.
Moreover, comparisons to an independent data set are also of great interest to detect drifts and biases. The usefulness of tide gauge data networks for calibrating satellite altimetry systems was demonstrated by several authors (Mitchum [1994, 2000], Chambers et al. , Cazenave et al. …). We took over the works of the above authors and improved them to compare altimeter measurements with a specific tide gauge database (Badomar) processed at CLS. Selecting tide gauge stations where the differences between altimetry heights and tide gauge sea levels are small, is essential to get good variance estimates. The methodology of the comparisons of altimeter data against tide gauge measurements is now operational and produces results routinely for all altimetry missions.