Unprecedented Monitoring of the Water Levels in the Ungauged Congo Basin Using Satellite Altimetry.

Abstract:

Despite the global importance of the Congo Basin, which is the second largest river basin in the world, the limited understanding of its hydro-climatic patterns is in part due to the lack of in-situ monitoring of climate variables there. Climate and hydrological station networks are sparse and poorly maintained; the few networks that were implemented during the colonial period have shrunk considerably. Conversely, the recent improvements in remote sensing technology provide more observations than ever before that can advance hydrological studies, particularly in tropical basins. This work provides the first monitoring of water level at the basin scale for the Congo Basin based on merged data from different altimetry missions: ENVISAT, Jason-2 and SARAL. More than 500 time series of water level are computed for a twenty of contributors, over the period of 2002 to 2010 for 200 ENVISAT series, including using the second orbital period, from 2008 for 75 Jason-2 series and from mid 2013 for 250 SARAL series. The consistency and the quality of this datasets are investigated. First, the ENVISAT and J2 series are compared to in-situ measurements where possible. SARAL is the very first mission collecting water levels over rivers in the Ka band. Therefore, in a second step, we compare the capability of its altimeter AltiKa to that of previous missions working in the Ku band such as ENVISAT and Jason-2 in retrieving water levels over the Congo basin. In the last part of the work, we investigate the river dynamics in the Congo Basin since 2002 until today, using the Multichannel SSA (MSSA) to provide information about the common temporal variability of the dominant variables among the water level datasets.