CoAuthors

Frédéric Frappart (GET/OMP/LEGOS, France); Adama Telly Diepkilé (DER Math-Informatique, Mali); Vincent Marieu (EPOC, UMR 5805, France); Eric Mougin (GET, France); Fabien Blarel (LEGOS, France); Bertrand Lubac (EPOC, UMR 5805, France); Nadine Braquet (IRSTEA/IRD, France); Abdramane Ba (LOSSA, Mali)

Radar altimetry provides unique information on water stages of inland hydro-systems. In this study, performances of seven altimetry missions, among the most commonly used in land hydrology (i.e., European Remote-Sensing Satellite-2 (ERS-2), ENVIronment SATellite (ENVISAT), Satellite with Argos and ALtika (SARAL), Jason-1, Jason-2,Jason-3 and Sentinel-3A), are assessed using records from a dense in situ network composed of 19 gauge stations in the Inner Niger Delta (IND) from 1995 to 2017. Results show an overall very good agreement between altimetry-based and in situ water levels with correlation coefficient (R) greater than 0.8 in 80% of the cases and Root Mean Square Error (RMSE) lower than 0.4 m in 48% of cases. Better agreement is found for the recently launched missions such as SARAL, Jason-3 and Sentinel-3A than for former missions, indicating the advanceof the use of the Ka-band for SARAL and of the Synthetic-aperture Radar (SAR) mode for Sentinel-3A. Cross-correlation analysis performed between water levels from the same altimetry mission leads to time-lags between the upstream and the downstream part of the Inner Niger Delta of around two months that can be related to the time residence of water in the drainage area.

Keywords: altimetry; water levels; validation; Inner Niger Delta