Altimetry helps to monitor the Congo basin

Image of the Month - February 2021

Upper panel: interest points for Water Surface Elevation conversion into discharge from rating curves. Colored dots are satellite altimetry Virtual Stations. Lower panel: Estimated discharges from the different altimetry satellites (Bight blue and yellow dots S3-A, green squares S3-B, Navy blue dots Jason-3) and in situ stations; Purple dashed line is daily discharge at Kisangani (300 km upstream) from CICOS. Red dashed line (right axis) is daily discharge at Brazzaville/Kinshasa from Hybam. (from [Paris et al., 2021]) (Credit Cnes/Legos/CLS/Ocean Next)
Upper panel: interest points for Water Surface Elevation conversion into discharge from rating
curves. Colored dots are satellite altimetry Virtual Stations. Lower panel: Estimated discharges from the different altimetry satellites (Bight blue and yellow dots S3-A, green squares S3-B, Navy blue dots Jason-3) and in situ stations; Purple dashed line is daily discharge at Kisangani (300 km upstream) from CICOS. Red dashed line (right axis) is daily discharge at Brazzaville/Kinshasa from Hybam. (from [Paris et al., 2021]) (Credit Cnes/Legos/CLS/Ocean Next)
Location of the in situ and virtual stations used in the study. Yellow, Red and Blue squares & diamonds, green dots & violet hexagons are the virtual stations, while brown squares and the purple triangles are in situ stations. The drainage network extracted of the DEM using IPH-HydroTools, background OpenStreetMaps (from [Paris et al., 2021]) (Credit Cnes/Legos/CLS/Ocean Next)
Location of the in situ and virtual stations used in the study. Yellow, Red and Blue squares & diamonds, green dots & violet hexagons are the virtual stations, while brown squares and the purple triangles are in situ stations. The drainage network extracted of the DEM using IPH-HydroTools, background OpenStreetMaps (from [Paris et al., 2021]) (Credit Cnes/Legos/CLS/Ocean Next)

A number of river basins around the world are poorly gauged, for different reasons -- size of the basin, difficulties to reach some places, complexity of the watershed, physical landscape features, geopolitics, funding... The Congo River basin, in Equatorial Africa, is among them, while being the second largest basin on Earth. 
In the meantime, there as in any river basin, estimating the river discharge is of foremost importance for the residents, especially for flood control or mitigation, navigation and other situations where operational monitoring can help informed decision making.

To estimate such discharges in near-real time, a "rain-discharge" hydrological model has been tuned using both Earth Observation satellite products and in-situ data. It was run using satellite précipitation data. The daily discharges hence simulated by the model have been used in conjunction with satellite altimetry to build height - discharge rating curves at more than 500 sites spread all over the basin. These rating curves can now be used to convert automatically any new heights measured in the basin by one of the altimetry missions currently flying (Sentinel-3A & 3B, Jason-3 and soon Sentinel-6 Michael Freilich) into a discharge estimate. These discharge estimates over the Congo basin will be distributed in near-real time on Hydroweb.

The rating curves resulting from this study will also contribute to prepare for Swot, including for the Calval phase, with two track of the fast-sampling orbit crossing over the basin. 

See also:

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Reference:

  • A. Paris, S. Calmant, M. Gosset, A. Fleischmann, T. Conchy, P.-A. Garambois, J.-P.  Bricquet, F. Papa, R. Tshimanga, G. Gulemvuga, V. Siqueira, B. Tondo, R. Paiva, J. Santos da Silva, A. Laraque, 2021: Monitoring hydrological variables from remote sensing and modelling 1 in the Congo River basin, submitted to ,https://doi.org/10.1002/essoar.10505518.1