ENVISAT Altimetry Gives Access to an Unprecedent Dataset of Water Levels in the Amazon Bassin
Silva, Joecila1; Seyler, Frederique2; Calmant, stephane3

ENVISAT altimetry mission was the first mission to propose several estimates of the range for each radar measurement, at the 20Hz sampling rate (~ every 300m). Using the ranges derived by the ICE-1 tracking algorithm, we have derived ~800 series over the Amazon basin, over >50 rivers. All size of rivers could be sampled successfully, from the large reaches of the major contributors as wide as several kilometers to small tributary reaches as narrow as a few tens of meters. Much bigger than the gage network actually active or available in the basin, this dataset gives access to an unprecedent view of the spatial and temporal variations of the water levels through out the basin.
We present an assessment of the series quality, in particular for the narrowest reaches. Noteworthy, the errors are not increasing simply with the narrowness of the reaches, high accuracy series ( rms ~20cm) being obtained even for the narrowest reaches in some favorable cases. We also present some basic hydrological applications using this dataset, such as hydrograms, space and time variations of monthly slope along strike the river course, identification of the spatial distribution of extreme events -droughts and floods- that occured in the basin between 2002 and 2010, levelling of gage zero, and identification of step-like errors in the gage series.