High-Resolution Sea Surface Height Anomaly from Nadir Altimeters: Processing Improvements and Spectral Consistency with SWOT

Abstract. The Surface Water and Ocean Topography (SWOT) wide-swath satellite altimetry mission represents a major advance over conventional nadir-pointing altimetry in resolving small-scale ocean dynamics. Here, we demonstrate the potential of conventional altimeters such as Jason-2, Saral/AltiKa, Sentinel-3A in observing small-scale ocean dynamics by using High-Resolution Sea Surface Height Anomaly (SSHA_HR) products instead of classical Low-Resolution products. We analyse SSHA_HR wavenumber spectra around New Caledonia in the southwestern tropical Pacific – an important study site in the context of SWOT. This region is characterized by complex ocean dynamics, featuring high mesoscale activity and internal tides. The comparison of SWOT Sea Surface Height Anomaly spectrum with Saral/Altika and Sentinel-3A SSHA_HR spectra shows a good consistency between both nadir altimetric measurements for small scales down to 20 km wavelength. SSHA_HR power spectra exhibit mesoscale spectral slopes extending down to 60 km wavelength, highlighting the dominant Surface Quasi-Geostrophic dynamics in the surface layers, particularly present in austral winter while Quasi-Geostrophic dynamics prevail in austral summer. A second k-2 spectral slope emerges at smaller scales down to 30 km wavelength in accordance with the Garret and Munk spectrum. The spectral signatures of internal tides are visible over a broad range of wavelengths up to 150 km in summer when submesoscale activity is less energetic. This study highlights the value of these high-resolution along-track data for documenting fine scale dynamics over a long time period and their integration into operational systems in conjunction with SWOT data or once the SWOT mission has been completed.