In Situ Geometric Validation of SWOT Satellite Observations in Bass Strait, Australia

Abstract Here we validate the Surface Water and Ocean Topography (SWOT) satellite mission sea surface height (SSH) products using an array of nine GNSS buoys at the long‐term altimetry validation facility in Bass Strait. As a groundbreaking swath altimetry mission, the opportunities presented by SWOT are vast, but extensive and geographically diverse validation of data is required to ensure these new data are robustly understood and fit for purpose. The Bass Strait site provides a complementary validation target in a coastal shelf sea environment, with heritage back to the launch of TOPEX/Poseidon. We demonstrate the GNSS buoys can provide reliable SSH estimates with a differential‐SSH uncertainty of ∼5 mm. Over the shortest separation distances within our array of 10 km, we find an upper bound for the KaRIn SSH noise of 7.0 mm from the standard SWOT product with 2 km pixel size, and an upper bound of 13.0 mm from the unsmoothed product with 250 m pixels. Errors increase with larger separation distances, which we can partially attribute to errors in the present set of product geophysical corrections. The relative magnitude of these errors compared to instrument noise highlights that care must be taken when interpreting SWOT SSH and SSH anomaly fields. Finally, we find an absolute height bias of KaRIn SSH of −10.3 mm (standard deviation of 33 mm) and an RMSE of significant wave heights of 0.22 m, further demonstrating the outstanding performance of the KaRIn instrument over the challenging coastal environment of Bass Strait.