Zakharova et al. (2026) Exploring the potential of Sentinel-3 and Sentinel-6 SAR altimetry measurements for discharge estimation: Case studies from the Rhine and Po rivers

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-02-26
• Authors: Elena Zakharova, Luciana Fenoglio-Marc, K. Nielsen, Peter Thorne, Marco Restano, J. Benveniste
• DOI: 10.1016/j.jhydrol.2026.135211

Research Groups

• ICARUS Climate Research Centre, Maynooth University, Maynooth, Co. Kildare, Ireland
• EOLA, Toulouse, France
• Bonn University, Bonn, Germany
• Chalmers University of Technology, G¨oteborg, Sweden
• National Space Institute, Technical University of Denmark, Kgs. Lyngby, Denmark
• SERCO/ESRIN, Frascati (Roma), Italy
• European Space Agency - Directorate of Earth Observation Programmes, Frascati, Italy

Short Summary

This study investigates the potential of Sentinel-3 and Sentinel-6 SAR altimetry for discharge estimation in medium-sized rivers, using the Rhine and Po as case studies. It demonstrates that enhanced 80 Hz altimetry processing and rigorous data filtering significantly improve water level and discharge accuracy, achieving NRMSE values as low as 4% with empirical methods and 8% with refined physical models.

Objective

• To explore the potential of Sentinel-3A/B and Sentinel-6 SAR altimetry missions for river discharge estimation in medium-sized rivers (Rhine and Po), and to evaluate the impact of different discharge estimation approaches and altimetry data processing methods on accuracy.

Study Configuration

• Spatial Scale: Rhine and Po Rivers, characterized as medium-sized rivers (annual flows between 20 km³ and 100 km³).
• Temporal Scale: Data from Sentinel-3A, Sentinel-3B, and Sentinel-6 SAR altimetry missions, with the study period implicitly covering data available up to at least 2023.

Methodology and Data

• Models used:
  • Empirical rating curve (relating water level to in situ discharge)
  • Manning equation (physical method, with and without variable channel roughness)
  • Bjerklie equation (semi-empirical method, simplified physical laws, with regional adjustment of parameters)
  • Enhanced high-resolution 80 Hz processing of SAR altimetry signals
  • Rigorous satellite data selection and filtering protocols
• Data sources:
  • Sentinel-3A SAR altimetry measurements
  • Sentinel-3B SAR altimetry measurements
  • Sentinel-6 SAR altimetry measurements
  • Simultaneous in situ river discharge measurements (for calibration and validation)

Main Results

• Enhanced high-resolution 80 Hz processing of SAR altimetry signals and rigorous satellite data selection/filtering protocols significantly improve the accuracy of water level and subsequent discharge retrieval.
• Using an empirical rating curve, discharge estimation achieved an accuracy (Normalised Root Mean Square Error, NRMSE) of 4% to 16%, depending on the specific water level product.
• With a physical method based on the Manning equation, an accuracy of 11% to 26% NRMSE was attained. This improved to 8% to 22% NRMSE after incorporating a variable channel roughness term.
• A semi-empirical approach using the Bjerklie equation, after regional adjustment of its conductance and exponential parameters, demonstrated potential errors of approximately 10% NRMSE for the Rhine and Po Rivers.
• High-quality SAR altimetry-based discharge products could potentially detect discharge changes of 4% to 15%, which are projected for Europe by 2080 under the intermediate IPCC Shared Socio-economic Pathway scenario SSP2-4.5.

Contributions

• This study provides the first comprehensive exploration of Sentinel-3A/B and Sentinel-6 SAR altimetry for discharge estimation in medium-sized rivers, addressing a critical gap in satellite altimetry applications.
• It quantifies the benefits of advanced 80 Hz SAR altimetry processing and stringent data filtering for improving the accuracy of water level and discharge retrievals.
• The research systematically evaluates and compares the performance of empirical, physical, and semi-empirical discharge estimation methods using SAR altimetry for medium-sized rivers.
• It highlights the potential of SAR altimetry to contribute to monitoring and detecting climate change impacts on river discharge, particularly for medium-sized European rivers.

Funding

Not explicitly mentioned in the provided text.

Citation

@article{Zakharova2026Exploring,
  author = {Zakharova, Elena and Fenoglio-Marc, Luciana and Nielsen, K. and Thorne, Peter and Restano, Marco and Benveniste, J.},
  title = {Exploring the potential of Sentinel-3 and Sentinel-6 SAR altimetry measurements for discharge estimation: Case studies from the Rhine and Po rivers},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135211},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135211}
}