Examining the Performance of Satellite Altimetry (SWOT) Sea Level Data in the Coastal Areas of the Baltic Sea

Kupavõh, A.; Delpeche-Ellmann, N.; Ellmann, A., and Soomere, T., 2024. Examining the performance of satellite altimetry (SWOT) sea level data in the coastal areas of the Baltic Sea. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 534-538. Charlotte (North Carolina), ISSN 0749-0208. The Surface Water and Ocean Topography (SWOT) satellite mission is expected to bring new possibilities for detecting and assessing water level both at sea and land. To explore its performance, the SWOT nadir altimeter (Poseidon-3C) and the new Ka-band Radar Interferometer (KaRIn) were examined in coastal areas of the eastern Baltic Sea using the ‘Basic’ version in July–December 2023 using 15 geoid referred tide gauges (TG), vertical land uplift model and a high resolution geoid BSCD2000. The use of geoid enabled a direct comparison with TG data. Comparison with SA and TG was performed with varying distance from the TG. Specific examination of SWOT performance was made in areas affected by archipelagos, islands and sea ice. On average KaRIn altimeter RMSD values are around 13 cm compared to that of the nadir altimeter of 10 cm. One of the benefits of KaRIn is the improved spatial resolution of sea level data. It shows promising capabilities of detecting marine dynamics in the coastal areas. KaRIn altimeter showed improved performance in near-coast areas for within 40 km from TG, 97% of valid measurements were retrieved and within 0–2 km around 40% of valid data was obtained. Sea level was also accurately determined in ice covered areas.