Yaremchuk, MaxBeattie, Christopher A.Panteleev, GlebD’Addezio, Joseph2024-06-142024-06-142024-05-29Yaremchuk, M.; Beattie, C.; Panteleev, G.; D’Addezio, J. Block-Circulant Approximation of the Precision Matrix for Assimilating SWOT Altimetry Data. Remote Sens. 2024, 16, 1954.https://hdl.handle.net/10919/119442The recently deployed Surface Water and Ocean Topography (SWOT) mission for the first time has observed the ocean surface at a spatial resolution of 1 km, thus giving an opportunity to directly monitor submesoscale sea surface height (SSH) variations that have a typical magnitude of a few centimeters. This progress comes at the expense of the necessity to take into account numerous uncertainties in calibration of the quality-controlled altimeter data. Of particular importance is the proper filtering of <i>spatially</i> correlated errors caused by the uncertainties in geometry and orientation of the on-board interferometer. These “systematic” errors dominate the SWOT error budget and are likely to have a notable signature in the SSH products available to the oceanographic community. In this study, we explore the utility of the block-circulant (BC) approximation of the SWOT precision matrix developed by the Jet Propulsion Laboratory for assessment of a mission’s accuracy, including the possible impact of the systematic errors on the assimilation of the wide-swath altimeter data into numerical models. It is found that BC approximation of the precision matrix has sufficient (90–99%) accuracy for a wide range of significant wave heights of the ocean surface, and, therefore, could potentially serve as an efficient preconditioner for data assimilation problems involving altimetry observations by space-borne interferometers. An extensive set of variational data assimilation (DA) experiments demonstrates that BC approximation provides more accurate SSH retrievals compared to approximations, assuming a spatially uncorrelated observation error field as is currently adopted in operational DA systems.application/pdfenCreative Commons Attribution 4.0 Internationalsea surface heightswath altimetrySurface Water and Ocean Topography (SWOT)error covariancedata assimilationBlock-Circulant Approximation of the Precision Matrix for Assimilating SWOT Altimetry DataArticle - Refereed2024-06-13Remote Sensinghttps://doi.org/10.3390/rs16111954