SWOT-KaRIn Level-3 Products for coastal applications 

The DUACS system (Data Unification and Altimeter Combination System), developed as part of the CNES/SALP project, Copernicus Marine Service, and Copernicus Climate Change Service, provides high-quality multi-mission altimetry sea level products for oceanographic applications, climate forecasting centers, and the geophysics and biology communities. These products include user-friendly Level-3 (L3: along-track/swath cross-calibrated sea surface height anomalies [SSHA]) and Level-4 (L4: multi-sensor merged maps or time series) data.L3 algorithms originally designed for nadir altimeters have been extended to process SWOT swath altimeter data. Enhancements include state-of-the-art Level-2 corrections and models contributed by the research community, a data-driven and statistical approach to identifying and removing spurious or suspicious pixels, a multi-satellite calibration process leveraging the existing nadir altimeter constellation, and a noise-mitigation algorithm powered by a convolutional neural network. The L3 algorithms currently process both resolutions of the Level-2 LR product: 2 km and 250 m. These L3 products are freely accessible via the AVISO+ portal.This presentation aims to introduce the existing and upcoming L3 KaRIn products that can address coastal applications. Although currently based on LR measurements designed for open‑ocean use, L3 KaRIn products can also be relevant for certain coastal applications. The 250 m data processing enables observations close to the coastline; the availability of several variables allows users to adjust the physical content of the measurement; and a quality flag based on multiple criteria makes it possible to refine data selection. In addition, L3 products benefit from improved calibration that best corrects KaRIn systematic errors and ensures consistency across all altimetric missions. Finally, L3 products are regularly updated to incorporate state‑of‑the‑art processing methods and to adapt the products to users’ specific needs. Thus, a future line of L3 KaRIn products dedicated to coastal needs and possible based on upstream HR may be developed in 2026-2027.