SWOT Geostrophic Velocity Validation against in-situ measurements in the California Current

The Surface Water and Ocean Topography (SWOT) mission offers unprecedented high-resolution sea surface height (SSH) data, crucial for enhancing our understanding of ocean circulation dynamics. A key objective of SWOT is to convert SSH measurements into ocean velocity estimates. However, deriving reliable velocity estimates from such fine-scale SSH measurements is challenging, and the approach requires rigorous validation. This study evaluates the performance of SWOT in capturing geostrophic velocities within the California Current System (CCS) at 125.044oW, 35.917oN by comparing them to in-situ velocity measurements during the post-launch Calibration and Validation (CalVal) phase, from April 1st to July 4th, 2023. Results indicate that SWOT-derived velocities successfully capture variability at periods greater than 6 days, outperforming conventional satellite altimetry products that capture signals > 25-30 days. The root mean square difference (RMSD) between velocities from SWOT and in-situ measurements is significantly lower, with up to a 58% reduction compared to the in-situ standard deviation. The RMSD for SWOT is 4.2 cm/s, 4.2 cm/s, and 2 cm2/s2 for ug, vg, and EKE, respectively, compared to 4.7 cm/s, 5.8 cm/s, and 2.4 cm2/s2 for conventional altimetry-derived geostrophic velocities. These findings demonstrate SWOT's capability in resolving fine-scale ocean features and validate its potential to advance our understanding of ocean circulation, also highlight the challenges before fully utilizing SWOT's potential in studying ocean circulation in regions with higher internal gravity waves.