Jiaming Chen, Luciana Fenoglio, Jürgen Kusche, Jingjuan Liao, Hakan Uyanik, Zulfikar Adlan Nadzir, Yanhan Lou
Satellite radar altimetry is an important tool for monitoring water levels of inland water bodies, particularly in poorly gauged or ungauged areas. This study reveals for the first time the performance of water levels derived from Sentinel-3A altimetry in the Songhua River Basin in northeast China. This study compares water levels derived via different retrackers (SAMOSA+, OCOG, Ocean, MWaPP, and NPPR) from altimetry in virtual stations (VSs) to water levels measured by gauges. To improve the influence of sandbars or islands and surrounding land cover, a modified retracker called AMPD-PF (Automatic Multiscale-based Peak Detection retracker using Physically-based model Fitting) is implemented here, by combing the physical modeling of SAR altimeter waveform with a shortest-path algorithm to find the best possible sub-waveform representing the signal of water bodies. The accuracy assessment is based on comparing water level anomalies from 26 VSs and those from the nearest adjacent gauges with an average distance of 8.98 km in the Songhua River Basin from 2016 to 2019. The median of the root-mean-square error (RMSE) differences at the virtual stations ranges from 0.46 to 0.82 m, and the median of the Nash-Sutcliffe efficiency (NSE) among different retracker varies from 0.49 to 0.85 among different retracker. The performance of Sentinel-3A altimetry in the Songhua River Basin is not poor. Results also show a highest accuracy of water levels from AMPD-PF, especially for the non-flood season (January to June and October to December). In addition, we find that, especially for the virtual stations unaffected by the sand bars and islands, AMPD-PF give the best performance with a median RMSE value of 0.33 m and a median NSE value of 0.86. Factor analysis indicates that the variations of these metrics can not be directly related to the river width but might be related to the cultivated land types and the presence of sand bars and islands in the vicinity of rivers over the Songhua River Basin. Moreover, it is confirmed that a near-parallel orientation of the river with respect to the satellite ground track often leads to poorer performance at virtual stations. This suggests that if one is aiming at calibrating a hydrodynamic or hydrological model by combining altimetry, the VSs with the near-parallel orientation are not necessary to be considered when the percentage of the non-parallel crossings of all crossings is big enough. © 2023 Elsevier B.V.
Institute of Geodesy and Geoinformation, University of Bonn, Bonn, Germany; International Research Center of Big Data for Sustainable Development Goals, Beijing, China; Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China; Geomatics Engineering Department, Institute Teknologi Sumatera, South Lampung, Indonesia
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