Regional in situ validation of satellite altimeters: Calibration and cross-calibration results at the Corsican sites

Keywords

Altimeter calibration; Regional method; Tide gauges

Key figures

RegionalCalFig1 — Generic diagram of the regional *in situ* calibration. The points A and B represent the crossover points, respectively, the satellite altimeter tracks 1 and 2, and the tracks 2 and 3. The tracks can belong to different altimeter missions. The *in situ* high resolution mean surface is used to link the tide gauge (TG) measurements to the altimeter data, and the comparison is done at the point C, located on this surface.

RegionalCalFig2 — Geodetic references for the altimeter and tide gauge measurements. The altimeter SSH is directly evaluated with reference to the ellipsoid, so it integrates the solid, polar and loading tides variations. Consequently, the altimeter SSH must be corrected from these effects. On the contrary, the tide gauge is fixed to the ground and moves with it, undergoing the variations due to these phenomena.

Abstract

The in situ validation of the satellite altimeter sea surface heights is generally performed either at a few local points directly flown over by the satellites or using the global tide gauge network. A regional in situ calibration method was developed by NOVELTIS in order to monitor the altimeter data quality in a perimeter of several hundred kilometres around a given in situ calibration site. The primary advantage of this technique is its applicability not only for missions flying over dedicated sites but also for missions on interleaved or non repetitive orbits. This article presents the altimeter bias estimates obtained with this method at the Corsican calibration site, for the Jason-1 mission on its nominal and interleaved orbits as well as for the Jason-2 and Envisat missions. The various regional bias estimates (8.2 cm and 7.4 cm for Jason-1 respectively on the nominal and interleaved orbits in Senetosa, 16.4 cm for Jason-2 in Senetosa and 47.0 cm for Envisat in Ajaccio, with an accuracy between 2.5 cm and 4 cm depending on the mission) are compared with the results obtained by the other in situ calibration teams. This comparison demonstrates the coherency at the centimetre level, the stability and the generic character of the method, which would also be of benefit to the new and future altimeter missions such as Cryosat-2, SARAL/AltiKa, Sentinel-3, Jason-3, Jason-CS.