Abstract's details
Global assessment of SWOT small-scale performance via synergy with surface chlorophyll observations
Event: 2025 SWOT Science Team Meeting
Session: Oceanography: Calibration and Validation
Presentation type: Oral
Currently, one of the main challenges with SWOT observations lies in assessing the nature of the small-scale features detected by KaRIn and determining the extent to which the sea level signals observed at scales below 100 km can be associated with surface ocean currents. To address this challenge, we investigated the spatial correlations between SWOT L3 2 km sea surface height (SSH) from the “Science” Phase (21-day repetitive orbit) and remotely sensed surface Chlorophyll concentration (CHL). Our approach is based on the underlying hypothesis that the spatial patterns of the two fields are closely linked: assuming geostrophic balance, SSH is directly associated with surface velocities, which in turn (at least to a first order) regulate the dispersion and spatial distribution of CHL.
The chlorophyll concentrations used in our study are from the CMEMS GlobColour multi-satellite product. As this product offers kilometer-scale resolution, it has the capability to resolve sea surface structures analogous to those observed by SWOT. A comparison between DUACS SSH and CHL was also included in the analysis and used as a reference.
Our analysis focused on the spatial distribution of the correlation coefficient between SSH (both SWOT and DUACS) and CHL over segments of 120 km along the SWOT swath. Initial results indicated that the correlation patterns were predominantly influenced by the large-scale meridional gradient. Therefore, both altimetry and chlorophyll fields were band-pass filtered to isolate scales between 15 and 100 km.
Our results evidenced that the SSH/CHL correlations obtained for the unfiltered products have overall similar values and geographical patterns for both DUACS and SWOT products. The strongest negative correlations are found over the upwelling regions and western boundary currents, while strong positive ones occur in the subtropical bands of southern Indian and pacific oceans. The same comparison performed with the band-pass filtered fields shows strongly degraded performance for the DUACS product, while the SWOT one maintains higher correlations coefficients and similar geographical distribution. This suggests that SWOT observations better capture small-scale circulation features between 15 and 100 km across most of the global ocean.
A notable exception is the equatorial band where the DUACS product shows stronger correlations. Detailed analysis of the SSH fields indicated that in this band the small scales observed by SWOT are predominantly unbalanced signals (e.g. internal waves) which are not associated with surface currents and, consequently, do not affect the distribution of the surface CHL field.
Back to the list of abstractThe chlorophyll concentrations used in our study are from the CMEMS GlobColour multi-satellite product. As this product offers kilometer-scale resolution, it has the capability to resolve sea surface structures analogous to those observed by SWOT. A comparison between DUACS SSH and CHL was also included in the analysis and used as a reference.
Our analysis focused on the spatial distribution of the correlation coefficient between SSH (both SWOT and DUACS) and CHL over segments of 120 km along the SWOT swath. Initial results indicated that the correlation patterns were predominantly influenced by the large-scale meridional gradient. Therefore, both altimetry and chlorophyll fields were band-pass filtered to isolate scales between 15 and 100 km.
Our results evidenced that the SSH/CHL correlations obtained for the unfiltered products have overall similar values and geographical patterns for both DUACS and SWOT products. The strongest negative correlations are found over the upwelling regions and western boundary currents, while strong positive ones occur in the subtropical bands of southern Indian and pacific oceans. The same comparison performed with the band-pass filtered fields shows strongly degraded performance for the DUACS product, while the SWOT one maintains higher correlations coefficients and similar geographical distribution. This suggests that SWOT observations better capture small-scale circulation features between 15 and 100 km across most of the global ocean.
A notable exception is the equatorial band where the DUACS product shows stronger correlations. Detailed analysis of the SSH fields indicated that in this band the small scales observed by SWOT are predominantly unbalanced signals (e.g. internal waves) which are not associated with surface currents and, consequently, do not affect the distribution of the surface CHL field.