Quality analysis of water level series obtained by altimetric radar satellite along the São Francisco River

Abstract

Radar altimeters are instruments carried on space missions and allow for determination of heights, particularly in oceans and ice sheets. The use of altimetry data on continental waters involves several challenges, such as the revisit frequency (typically 27 to 35 days), an accuracy of decimeters, data handling and processing, particularly for narrow rivers such as the São Francisco River (width<1km). Radar satellite altimetry has advantages over the conventional in situ monitoring network, including in terms of spatial coverage and global altimetric reference of data. Thus, altimetry data should be used as a complementary and/or alternative source to in situ data. In this context, this study consolidates and evaluates the altimetric series of five different altimetry missions: Envisat in two orbits, Saral, Sentinel 3-A, and Sentinel 3-B. The altimetry water level time series of 17 Virtual stations were compared with leveled gauging stations series to calculate absolute and relative errors. Ultimately, the errors varied from 0.13 m to 0.36 m in the best cases (41%), in line with recent literature. Sentinel-3 satellites showed the best RMSE absolute/relative results: 0.95/0.49 m (S-3A) and 0.96/0.52 m (S-3B). The second best RMSEs was Envisat-X (1.39/0.50 m), then Envisat (1.87/0.56 m) and Saral (1.74/0.60 m).