Turki et al. (2025) On the use of SWOT altimetry data for monitoring coastal hydrodynamics

Identification

• Journal: International Journal of Applied Earth Observation and Geoinformation
• Year: 2025
• Date: 2025-11-29
• Authors: Imen Turki, Md. Saiful Islam, Carlos López Solano, Edward Salameh, Muricy Domingues, E. Tonatiuh Mendoza, Lotfi Aouf, Laurent Froideval, ‪Damià Barceló, Benoı̂t Laignel, Aurélien Carbonnière, Frédéric Frappart
• DOI: 10.1016/j.jag.2025.104982

Research Groups

• Univ Rouen Normandie, Université Caen Normandie, CNRS, Normandie Univ, M2C UMR 6143, France.
• Cerema, RHITME Research Team, Margny Les Compiègne, France.
• Meteo-France, DIROP-CNRM, Toulouse, France.
• Institute of Marine Sciences (IMS), University of California Santa Cruz, USA.
• Centre National d’Études Spatiales (CNES), Toulouse, France.
• ISPA, UMR1391 INRAE Bordeaux Science Agro, Villenave d’Ornon, France.

Short Summary

This study evaluates the accuracy of the Surface Water and Ocean Topography (SWOT) mission in retrieving coastal Sea Surface Heights (SSH) and Significant Wave Heights (SWH) in the English Channel. The findings demonstrate that SWOT provides high-resolution, reliable hydrodynamic data even within 3–4 km of the shoreline, significantly outperforming conventional satellite altimetry in complex nearshore environments.

Objective

• To assess the accuracy and precision of SWOT KaRIn interferometric products for monitoring coastal sea levels and wave heights, particularly during extreme storm events, at regional and local scales.

Study Configuration

• Spatial Scale: Regional scale covering the English Channel (UK and French coasts), with local-scale focus on nearshore zones (0–15 km from the coast).
• Temporal Scale: March 2023 to July 2024, encompassing the 1-day repeat Cal/Val phase and the 21-day repeat Science Orbit phase, including five major storm events (Mathis, Noah, Ciaran, Karlotta, and Pierrick).

Methodology and Data

• Models and Products used: SWOT Level-2 (L2) Low Rate (LR) "Expert" products derived from the Ka-band Radar Interferometer (KaRIn); versions PGC0, PIC0, and PIC2.
• Data sources:
  • Satellite: SWOT interferometric acquisitions (SSH and SWH).
  • In-situ: 16 tide gauges (BODC and SHOM networks) and 10 wave buoys (Copernicus/Met Office/SHOM).
  • Video Monitoring: Shoreline water level extraction via a Timex video system at the Semaphore station (Raz Blanchard).
  • Bathymetry: EMODnet Digital Terrain Model (DTM).

Main Results

• Statistical Accuracy: SWOT-derived SSH and SWH showed strong consistency with in-situ data, yielding a mean Root Mean Square Error (RMSE) of ≈0.9 m, a mean Standard Deviation (STD) of ≈0.85 m, and a correlation coefficient (R²) of ≈0.95.
• Coastal Proximity: SWOT wave estimates remained reliable within 3–4 km of the shoreline at water depths of approximately 8–12 m.
• SSH Performance: At specific stations like Dielette (4 km offset), the RMSE was as low as 0.2 m. Accuracy decreased as the spatial offset from the satellite track increased beyond 20 km.
• SWH Limitations: Early product versions (C0) struggled to capture small waves (<0.5 m) due to volumetric correlation algorithm limitations, though this was improved in later PIC2 iterations.
• Storm Monitoring: SWOT successfully captured extreme hydrodynamic signatures during major storms, providing 2D spatial maps of wave field evolution across the Channel.

Contributions

• Provides one of the first comprehensive validations of SWOT's wide-swath interferometric data in a macro-tidal, complex coastal environment.
• Demonstrates that SWOT can bridge the "coastal gap" where traditional nadir altimetry fails due to land contamination and signal distortion.
• Validates the use of SWOT for improving the fidelity of regional coastal numerical models and enhancing hazard monitoring for coastal communities.

Funding

• French Space Agency (CNES) via the TOSCA program (SWOT4COST).
• INSU program (EONES-SWOT).
• TRANSITIN FRANCE 2030 (Reference: ANR-23-EXES-0013).

Citation

@article{Turki2025use,
  author = {Turki, Imen and Islam, Md. Saiful and Solano, Carlos López and Salameh, Edward and Domingues, Muricy and Mendoza, E. Tonatiuh and Aouf, Lotfi and Froideval, Laurent and Barceló, ‪Damià and Laignel, Benoı̂t and Carbonnière, Aurélien and Frappart, Frédéric},
  title = {On the use of SWOT altimetry data for monitoring coastal hydrodynamics},
  journal = {International Journal of Applied Earth Observation and Geoinformation},
  year = {2025},
  doi = {10.1016/j.jag.2025.104982},
  url = {https://doi.org/10.1016/j.jag.2025.104982}
}

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