Validation of the altimetry-based water levels from Sentinel-3A and B in the Inner Niger Delta

Abstract

Abstract. The comprehension of water level fluctuations and the sustainability of the Inner Niger River Delta (IND) is a major concern for the scientific community, but also for the local population. Located in the centre of Mali, the heart of the Sahel, the delta is characterised by a floodable area of more than 32 000 km2 during the rainy season, which contributes very strongly to the vitality of local ecosystem, and is consequently classified as a Ramsar site under the international Convention for Wetlands. In addition, the Delta acts as an environmental and socio-economic development barometer for the entire sub-region. Nowadays, we can observe an increasing fragility of the delta due to climate change, desertification and human activities, and justifies the need for permanent monitoring. The present study is based on the recent successes of radar altimetry, originally designed to monitor the dynamics topography of the ocean, and now very frequently used to retrieve inland water levels, of lakes, rivers, and wetlands. Previous studies evaluated the performances of several radar altimetry missions including Low Resolution Mode (LRM) (Topex-Poseidon, Jason-1/2/3, ERS-2, ENVISAT, and SARAL, and Synthetic Aperture Radar (SAR) Sentinel-3A missions for water level retrievals over 1992–2017. More than 50 times series of water levels were build at the crossing between water bodies and Sentinel-3A and 3B over 2016–2020. Twenty-four comparisons between in-situ and altimetry-based time-series of water levels were achieved over the IND. RMSE generally lower than 0.7 m and r higher than 0.9 were obtained.

Inland Water Level Monitoring from Satellite Observations: A Scoping Review of Current Advances and Future Opportunities

“…Between 2018 and 2022, official retrackers from different radar altimetry missions are used in twentyone publications. In five publications [134][135][136][137][138] only data from the Sentinel-3 mission were used and its performance was validated by comparing in-situ gauge data with the altimetry-based water levels. In [134] it is shown that water level variations based on the empirical OCOG [117] retracker are significantly better than the physical Ocean [122] method.…”

Inner Niger Delta Inundation Extent (2010–2022) Based on Landsat Imagery and the Google Earth Engine

“…The most widely used multitemporal and multispectral satellite observations for this purpose are derived from Landsat (LS) [7][8][9][10], Sentinel [11][12][13], Moderate Resolution Imaging Spectroradiometer (MODIS) [6,[14][15][16], and SPOT (Satellite Pour l'Observation de la Terre) [17,18]. Much of the available literature on water-body extraction focusses on one type of water body (e.g., lakes, rivers, etc.)…”