Monitoring water levels and discharges using radar altimetry in an ungauged river basin : the case of the Ogooue Bogning, S. Frappart, F. Blarel, F. /Nino, Fernando /Mahé, Gil /Bricquet, Jean-Pierre /Seyler, Frédérique Onguene, R. Etame, J. Paiz, M. C. /Braun, Jean-Jacques altimetry water level discharge 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. 2018 text https://www.documentation.ird.fr/hor/fdi:010072663 fdi:010072663 Bogning S., Frappart F., Blarel F., Nino Fernando, Mahé Gil, Bricquet Jean-Pierre, Seyler Frédérique, Onguene R., Etame J., Paiz M. C., Braun Jean-Jacques. Monitoring water levels and discharges using radar altimetry in an ungauged river basin : the case of the Ogooue. 2018, 10 (2), art. 350 [18 ] EN GABON