Monitoring the Elbe estuary and coastal zone with SWOT and nadir-altimeters

Coastal-to-land sites are mostly affected by climate changes and are at multi-risks due to coastline retreat, flooding storms and river floods. New altimeter processing and new missions open new possibilities to observe fine-scale spatial changes in this region. Our hypothesis is that new altimetry remote sensing observations from the Delay Doppler nadir-altimetry and wide swath altimetry can make an unprecedented progress at monitoring the river-to-ocean continuum and understanding estuarine and coastal hydrodynamic processes. Aim of this study is the interaction between river discharge and coastal sea level in the Elbe estuary and tidal river. Region of analysis are the German coasts and Elbe estuary and tidal river. This last is under the SWOT cal/val track. SWOTs unique, high-resolution 2D observations, combined with the field campaign data, other satellite data and models, is expected to provide a new view of many dynamical phenomena from ocean and nearshore zones to coastal and estuarine contexts. We consider the Fully-Focus (FF-SAR) processing near coast. We show that results depend on the retracking method and that land contamination is also affecting FF-SAR. The SAMOSA+ retracker gives the best results for both FFSAR and unfocused SAR (USAR). The ability of regional ocean models to reproduce tides and the high variability at fine spatial-scale is investigated. Ocean simulation sea level is compared to nadir-altimetry along the satellite ground tracks. We show that while the coverage of nadir-altimeter is limited by the number of ground-tracks, SWOT, that provides a uniform coverage, is less affected by land contamination. We investigate the SWOT mission data. First results with low resolution 2 km x 2 km data indicate good agreement with in-situ gauges with 20-30 cm standard deviation from in-situ tide gauge stations. SWOT enhanced resolution data at 250m x 250m and higher resolution data are further investigated to more accurately monitor nearshore, estuarine, and the sea-ice interface. Due to the differences between along-track and swath-altimetry, new methods to derive accuracy and precision of the measurements and derived ocean parameters are developed. Using a large network of in-situ, model and nadir-altimetry data we perform the calibration and the validation of the SWOT products assessing the relevance of SWOT for improving numerical models over all the Elbe tidal river. We would be interested in submitting our presentation to a peer reviewed special issue in Ocean Sciences.