Accuracy Assessment of SWOT Wind and Wave Data by Comparison With Buoy and Nadir Altimeter Data

Satellite altimeters serve as pivotal instruments for extensive, simultaneous observations of ocean wind and wave. The Surface Water and Ocean Topography (SWOT) satellite, launched in December 2022, which is equipped with a Ka-band Radar Interferometer (KaRIn), enables two-dimensional, wide-swath data of ocean wind speed (WS) and significant wave height (SWH). This study provides an assessment of the accuracy and stability of SWOT WS and SWH data from November 23, 2023 to March 31, 2025, by comparing with buoy data from the National Data Buoy Center (NDBC), Tropical Atmosphere Ocean (TAO), Pilot Research Moored Array in the Tropical Atlantic (PIRATA), and the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA), as well as data from nadir altimeters which include Jason-3, Sentinel-3A/B and Sentinel-6A. The accuracy assessment results show that the SWOT WS has bias from -0.48 to -0.96 m/s and root mean square error (RMSE) of 1.21-1.79 m/s relative to buoy data, with relatively higher accuracy at WS of 2–9 m/s. SWOT SWH has bias of 0.01 m and RMSE of 0.59 m, with slightly lower accuracy than nadir altimeters. Compared to nadir altimeters, SWOT WS has bias from -0.15m/s to -0.30m/s and RMSE of 1.17–1.76 m/s. SWOT WS are slightly higher at low WS and marginally lower at high WS relative to nadir altimeters. SWOT SWH has bias from -0.06 to - 0.15 m and RMSE of 0.42–0.69 m. Additionally, the SWOT WS and SWH data show similar consistent characteristics when compared with the same series of satellite altimeter data. Overall, the accuracy assessment demonstrates that SWOT provides reliable WS and SWH data under most oceanic conditions. Its capability for wide-swath, synchronous WS and SWH data collection offers valuable support for ocean wind and wave monitoring over the global ocean.