Comparison of Methods to Derive the Height-Area Relationship of Shallow Lakes in West Africa Using Remote Sensing

Abstract

In West Africa, lakes and reservoirs play a vital role as they are critical resources for drinking water, livestock, irrigation, and fisheries. Given the scarcity of in-situ data, satellite remote sensing is an important tool for monitoring lake volume changes in this region. Several methods have been developed to do this using water height-area-volume relationships, but few publications have compared their performances over small and medium-sized shallow lakes. In this work we compare four methods based on recent data from high-resolution optical imagery and radar and lidar altimetry over 16 lakes in the Central Sahel, with areas between 0.22 ${\text{km}}^2$ and 21 ${\text{km}}^2$. All methods show consistent results and are generally in good agreement with in-situ data in terms of accuracy (Root Mean Squared Error below 0.42 m for heights and Normalized Root Mean Squared Error below 13% for volumes). The precision of the estimated water height is about 0.20 m for Pleiades Digital Surface Models (DSMs) and less than 0.13 m for the other methods. Inherent limitations such as DSM quality, temporal coverage of DSM and lidar data, and spatial coverage of radar altimetry data are identified. Overall, fine shape patterns are consistently observed over small height amplitudes, highlighting the ability to monitor shallow lakes with non-linear height-area relationship. Finally, we show that combining lidar and radar altimetry-based methods provides estimates of volume changes over the different water bodies of the study region accurate enough to monitor seasonal, interannual, and long-term variability.