Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Remote Sensing art. 350 [18 ] altimetry water level discharge GABON OGOUE BASSIN 2018 fdi:010072663 ENG Remote Sensing 2072-4292 ISI:000427542100194 2 10.3390/rs10020350 https://www.documentation.ird.fr/hor/fdi:010072663 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers18-04/010072663.pdf 10 Horizon (IRD) Radar altimetry is now commonly used for the monitoring of water levels in large river basins. In this study, an altimetry-based network of virtual stations was defined in the quasi ungauged Ogooue river basin, located in Gabon, Central Africa, using data from seven altimetry missions (Jason-2 and 3, ERS-2, ENVISAT, Cryosat-2, SARAL, Sentinel-3A) from 1995 to 2017. The performance of the five latter altimetry missions to retrieve water stages and discharges was assessed through comparisons against gauge station records. All missions exhibited a good agreement with gauge records, but the most recent missions showed an increase of data availability (only 6 virtual stations (VS) with ERS-2 compared to 16 VS for ENVISAT and SARAL) and accuracy (RMSE lower than 1.05, 0.48 and 0.33 and R-2 higher than 0.55, 0.83 and 0.91 for ERS-2, ENVISAT and SARAL respectively). The concept of VS is extended to the case of drifting orbits using the data from Cryosat-2 in several close locations. Good agreement was also found with the gauge station in Lambarene (RMSE = 0.25 m and R-2 = 0.96). Very good results were obtained using only one year and a half of Sentinel-3 data (RMSE < 0.41 m and R-2 > 0.89). The combination of data from all the radar altimetry missions near Lamabrene resulted in a long-term (May 1995 to August 2017) and significantly improved water-level time series (R-2 = 0.96 and RMSE = 0.38 m). The increase in data sampling in the river basin leads to a better water level peak to peak characterization and hence to a more accurate annual discharge over the common observation period with only a 1.4 m(3)s(-1) difference (i.e., 0.03%) between the altimetry-based and the in situ mean annual discharge. 062 ; 126 UR065 / UR234 / UR050 / UR228 Cameroun / Gabon