Space and Time Variations of Lack Surface from Satellite Altimetry
Calmant, S.1; Cretaux, J-F2; Yi, Y3

In first approximation, assuming that flow is small enough for hydrodynamic slope to be negligeable, the surface of lakes is an equipotential of the Earth Gravity field. So, these lake surfaces folow a surface almost parallel to the geoid but not at constant ellipsoidal height. Hence, the absolute lake stage given by satellite measurements varies according to the location of the satellite pass. It is worth noting that the nowaday global gravity models such as GRACE have not the resolution required for the conversion the heights onto altitude are constant throughout the Lake surface. In order to enable joining all the satellite measurements of lake height in a unique time series, we have computed the geographical variations of lake heights using the collocation technique and the data of Geosat, ENVISAT,T/P, GFO,ICESat and JASON-1. As a by-product, time series and mission biases are produced ,as differences between the actual measurements and the computed reference lake height. In the specific case of the Issykul lake that we highlight, we use GPS data collected during in-situ cruises as a reference.


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