Monitoring Water Levels and Discharges Using Radar Altimetry in an Ungauged River Basin: The Case of the Ogooué

• Published in: Remote sensing (Basel, Switzerland) Vol. 10; no. 3; p. 350
• Main Authors: Bogning, Sakaros, Frappart, Frédéric, Blarel, Fabien, Niño, Fernando, Mahé, Gil, Bricquet, Jean-Pierre, Seyler, Frédérique, Onguéné, Raphaël, Etamé, Jacques, Paiz, Marie-Claire, Braun, Jean-Jacques
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.02.2018; MDPI
• Subjects: Accuracy; Altimeters; Altimetry; Data sampling; Discharge; Earth Sciences; Environmental Engineering; Environmental monitoring; Environmental Sciences; Hydrology; Missions; Monitoring; Radar; River basins; Rivers; Sciences of the Universe; Stations; water level; Water levels; water level; discharge; altimetry
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs10020350

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 Ogooué 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 R² 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 Lambaréné (RMSE = 0.25 m and R2 = 0.96). Very good results were obtained using only one year and a half of Sentinel-3 data (RMSE < 0.41 m and R2 > 0.89). The combination of data from all the radar altimetry missions near Lamabréné resulted in a long-term (May 1995 to August 2017) and significantly improved water-level time series (R² = 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 m3•s−1 difference (i.e., 0.03%) between the altimetry-based and the in situ mean annual discharge.