FY 2025

SWOT mission validation of sea surface height measurements at sub-100 km scales

Wang, J., A.J. Lucas, S. Stalin, M. Lankhorst, U. Send, O. Schofield, L. Kachelein, B. Haines, C. Meinig, R. Pinkel, J.T. Farrar, and L.-L. Fu

Geophys. Res. Lett., 52(11), e2025GL114936, doi: 10.1029/2025GL114936, View open access article at Wiley (external link) (2025)

After two decades of development, the Surface Water and Ocean Topography (SWOT) mission launched on 16 December 2022, pioneering the use of Ka-band Radar Interferometry (KaRIn) for measuring water surface elevation and achieving two-dimensional altimetry on two 50 km swaths separated by a 20 km nadir gap. Rigorous validation against in situ observations in this study demonstrates that KaRIn achieves enough accuracy to resolve sub-100 km oceanic processes, with measurement errors 2–4 times smaller than anticipated. These results confirm SWOT's transformative capabilities for advancing oceanographic research and establishing a robust foundation for future applications of the swath altimetry. The results also underscore the innovative advancements in mooring system design, driven by the stringent science requirements of the SWOT mission.

Plain Language Summary. After two decades of development, the Surface Water and Ocean Topography (SWOT) mission successfully launched its satellite on 16 December 2022. As a pioneering effort, SWOT introduced the use of the Ka-band Interferometer (KaRIn) to measure water surface elevation and advanced satellite altimetry to two-dimensional swath observations for the first time. Like any pathfinding mission, validation against independent ground-based measurements is essential to ensure the accuracy and reliability of its science objectives. This paper details the validation of KaRIn's performance within the framework of ocean physics, leveraging a conventional in situ oceanographic measurement network. The validation results demonstrate that KaRIn's true measurement error is 2–4 times better than initially anticipated. The instrument accurately captures sub-100 km oceanic processes with sub-centimeter accuracy. This achievement highlights SWOT's potential to revolutionize oceanographic research, providing a robust foundation for future scientific explorations enabled by its innovative interferometry-based measurement capabilities. It also demonstrates the capability of modern in situ mooring systems, which are specifically engineered for highly accurate observations of the ocean interior.