Increasing the space-time resolution of mapped sea surface height from altimetry

We present a new mapping methodology to improve the resolution of gridded sea surface height (SSH) using along-track multi-satellite measurements, and apply it in the California Current system. This is motivated by the upcoming Surface Water and Ocean Topography (SWOT) satellite mission, which will provide novel high-resolution wide-swath measurements of SSH. The calibration/validation of SWOT in the California Current requires independent observations of fine-scale 2D SSH variability. Currently, the best gridded SSH product for the region is AVISO’s global dataset, based on optimal interpolation (OI). Our new method is based on 2-dimensional variational analysis (2DVAR) and we address some limitations of the AVISO OI global parameterization that restrict the resolution. Key improvements are: (1) use of a background field incorporating mesoscale information, as opposed to a long-term mean field; (2) optimized regional parameters; and (3) a representation error term in the observational error covariance matrix to account for the spread of measurements in time. Using a suite of independent remote and in situ observations, we show that 2DVAR delivers a higher-resolution SSH field that captures finer-scale mesoscale ocean circulation in the California Current region, at the expense of an increase in noise.