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A global intercomparison of SWOT and traditional nadir radar altimetry for monitoring river water surface elevation
Publikationstyp
Journal Article
Date Issued
2026-03-01
Sprache
English
Author(s)
Xu, Yue
Frappart, Frédéric
Zhang, Guoqing
Lin, Peirong
Jiang, Liguang
Yao, Fangfang
Han, Xiaoran
Xia, Jun
Journal
Volume
334
Article Number
115219
Citation
Remote Sensing of Environment 334: 115219 (2026)
Publisher DOI
Scopus ID
ISSN
00344257
The water surface elevation (WSE) of rivers serves as fundamental data for various hydrological research and applications. The recently launched Surface Water and Ocean Topography (SWOT) satellite offers a revolutionary altimetry approach by providing wide-swath elevation mapping using a SAR Interferometer (InSAR) operating at Ka-band. While SWOT provides unprecedented spatio-temporal coverage of WSE, it has not been systematically compared with reference water stage databases. Currently, due to difficulties in accessing recent and globally homogenous gauge station records, established WSE derived from radar altimetry (RA) missions is the most suitable dataset to perform global validation of WSE. This study presents the first global-scale intercomparison of the two altimetry systems, the wide-swath InSAR technique used for the first time by SWOT and the classical along-track RA using the SAR technique, and identifies several representative factors influencing their consistency. SWOT WSE are compared with virtual stations derived from Sentinel-3 and Sentinel-6 missions, across five different node quality categories (“good”, “suspect”, “degraded”, “bad” and a combined “all” group without “bad” data). The analysis further examines the potential influences from river width, river ice, backscattering coefficients (sigma0), and dark water fraction in modulating data consistency. The root mean square error (and correlation coefficient) between WSE from SWOT and RA in “good” and “suspect” data are 0.80 m (0.85) and 1.62 m (0.78), respectively, while those for “degraded” and “bad” data rise significantly to 8.80 m (0.60) and 16.91 m (0.50). The combined “all” category yields an overall RMSE (CC) of 5.15 m (0.65). For rivers wider than 160 m, SWOT measurements with “good” and “suspect” quality demonstrate notably improved consistency with RA compared to narrower rivers. Under frozen conditions, the reduced consistency between SWOT and RA is most evident in the “degraded” and “bad” quality data, with average reductions in CC of 0.17 and 0.21, respectively. In addition, radar backscatter strongly impacts the quality of SWOT-based WSE, as both extremely low values (dark water) and very high values (specular ringing) can lead to unrealistic estimates. Overall, this study offers important insights into the global performance of SWOT-based WSE estimation and informs the future refinement and application of SWOT data in hydrological research.
Subjects
Altimetry
Intercomparison
River water level
SWOT
Water surface elevation
DDC Class
600: Technology