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

1
Département de Sciences de la Terre, Université de Douala, BP 24 157 Douala, Cameroun
2
Jeune Equipe Associée à l’IRD—Réponse du Littoral Camerounais aux Forçages Océaniques Multi-Échelles (JEAI-RELIFOME), Université de Douala, BP 24 157 Douala, Cameroun
3
LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS OMP, 14 Av. E. Belin, 31400 Toulouse, France
4
GET, Université de Toulouse, CNRS, IRD, UPS OMP, 14 Av. E. Belin, 31400 Toulouse, France
5
HydroSciences Montpellier, Université de Montpellier, CNRS, IRD, 300 Av. Pr E. Jeanbrau, 34090 Montpellier, France
6
ESPACE-DEV, Université de Montpellier, IRD, Université des Antilles, Université de Guyane, Université de La Réunion, Maison de la Télédétection, 500 Rue J-F. Breton, 34093 Montpellier, France
7
The Nature Conservancy Gabon Program Office, Lot 114 Haut de Gué-Gué, 13553 Libreville, Gabon
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(2), 350; https://doi.org/10.3390/rs10020350
Received: 30 January 2018 / Revised: 15 February 2018 / Accepted: 22 February 2018 / Published: 24 February 2018
(This article belongs to the Special Issue Satellite Altimetry for Earth Sciences)
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Abstract

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. View Full-Text
Keywords: altimetry; water level; discharge altimetry; water level; discharge
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Bogning, S.; Frappart, F.; Blarel, F.; Niño, F.; Mahé, G.; Bricquet, J.-P.; Seyler, F.; Onguéné, R.; Etamé, J.; Paiz, M.-C.; Braun, J.-J. Monitoring Water Levels and Discharges Using Radar Altimetry in an Ungauged River Basin: The Case of the Ogooué. Remote Sens. 2018, 10, 350.

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