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Calibration of T/P, Jason-1, Icesat, GFO and Envisat from GPS campaigns over the lake Issykkul, Khirghyztan
Cretaux, J-F1; Calmant, S.2; Romanovski, V.3; Shabunin, A3; Lyard, F.4; Bergé-Nguyen, M.5; Cazenave, A5; Hernandez, F.6
1CNES; 2IRD/LEGOS; 3; 4CNRS/LEGOS; 5CNES/LEGOS; 6IRD

The Topex /Poseidon satellite launched in 1992 and the following altimetry mission (Jason, GFO, Envisat) are widely used in the continental domain: lakes, rivers and wetland. Due to the high precision of the current altimeters, and thanks to progress in orbitography, altimetry hence became a fundamental tool to study continental water bodies. However the knowledge of the instrumental bias is also a key issue. Numerous calibration sites in the ocean field (Harvest offshore platform in California, Corsica, Bass strait in Australia) have been used for this purpose last years. Recently a calibration site on Lake Erie (USA) has also been used to evaluate altimeter bias of Topex Poseidon and Jason over continental area. One new site of calibration is presented: the lake Issykkul in Kirghizstan. This site has been chosen because it presents some interesting characteristics: the dynamic variability and wave are low, this lake is fully covered by all current altimetry satellites (Jason, Topex Poseidon, GFO, Icesat and Envisat), in-situ water level are available in the vicinity of the calibration site, and it allows to densify the pool of existing calibration site in the continental domain. 2 campaign with GPS receivers have been conducted on Issykkul lake (in 2004 and 2005), with receivers installed on a boat, and receivers on the shore. Cruises with GPS data along the ground track of each satellite were conducted. They enable estimating absolute bias of each altimeter, and relative bias between them. The GPS cruises are also used as a major constrain in mapping the mean lake surface that is very steep near the shore.

 

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