Matthias Raynal (CNES, France); Pierre Prandi (Collecte Localisation Satellites, France)

Analysis of SWOT observations collected during the early phase of the mission has confirmed that KaRIn is meeting many of its pre-launch expectations over the oceans. Mesoscale and submesoscale processes, including unbalanced dynamics, can now be successfully resolved down to spatial scales of just a few tens of kilometers. Moreover, the two-dimensional nature of KaRIn measurements enables improved representation of the shape and position of these structures. However, early studies have also revealed that some of the geophysical corrections applied to KaRIn observations may introduce errors with spatial characteristics similar to those of sea surface height anomalies (SSHA) at wavelengths below 100 km. Consequently, a major challenge in the current phase of the mission is to distinguish the true geophysical variability from residual measurement errors in the small-scale SSH signal observed by KaRIn.

Here we present a global assessment of the performance of KaRIn geophysical corrections, focusing specifically on Sea State Bias (SSB), Wet Tropospheric correction (WTC), Dynamic Atmospheric correction (DAT) and ocean tides. Our analysis is based on KaRIn Level-2, 2-km PGC0 observations from both Cal/Val and Science orbit phases. For SSB and WTC corrections, the performance of the KaRIn-based corrections is also compared against that from the model-based solutions. The study is complementary to others presented at this ST focusing on KaRIn corrections: in particular P. Abjean et al. (tropospheric signature), L. Carrere et al. (baroclinic tides), M. Tchilibou et al. (coherent and inchoerent tides) and C. Anadon et al. (xcal correction).

The first part of the analysis focused on the spatial characterization of correction performance. For each correction, the variance of uncorrected and corrected SSHA was computed over bins of 1° by 1°. The difference between these variances was used to quantify the proportion of SSHA variability absorbed by each correction, providing insights into its effectiveness and spatial variability, including across the KaRIn swath.

In the second part of the analysis, correction performance was assessed in the spectral domain. Specifically, along-track power spectral densities of the corrected SSHA, uncorrected SSHA, and the correction fields themselves were computed. Correction performance at different spatial scales was quantified by comparing the spectral energy reduction in the corrected versus uncorrected SSHA. This analysis was repeated across different oceanic regions to evaluate geographic variability. For corrections expected to exhibit cross-track variability, the analysis was also repeated at different cross-track distance within the KaRIn swath.

Overall, our results offer new insights into the geographical regions and dynamical conditions under which KaRIn geophysical corrections are most and least effective. This improved understanding can provide a decisive contribution for assessing the reliability of KaRIn observations in resolving small-scale oceanic variability.