Benefits of fully focused SAR altimetry to coastal wave height estimates: A case study in the North Sea
- 1Technische Universität München, Deutsches Geodätisches Forschungsinstitut, München, Germany (marcello.passaro@tum.de)
- 2Geoscience and Remote Sensing, Delft University of Technology, Stevinweg 1, Delft, 2628 CN, The Netherlands
Estimating the three geophysical variables significant wave height (SWH), sea surface
height, and wind speed from satellite altimetry continues to be challenging in the
coastal zone because the received radar echoes exhibit significant interference from
strongly reflective targets such as mud banks, sheltered bays, ships etc. Fully focused
SAR (FF-SAR) processing exhibits a theoretical along-track resolution of up to less
than half a metre. This suggests that the application of FF-SAR altimetry might give
potential gains over unfocused SAR (UF-SAR) altimetry to resolve and mitigate smallscale
interferers in the along-track direction to improve the accuracy and precision of
the geophysical estimates.
The objective of this study is to assess the applicability of FF-SAR-processed Sentinel-
6 Michael Freilich (S6-MF) coastal altimetry data to obtain SWH estimates as close as
possible to the coast.
We have developed a multi-mission FF-SAR processor and applied the coastal
retracking algorithm CORALv2 to estimate SWH. We assess different FF-SAR and UFSAR
processing configurations, as well as the baseline Level-2 product from
EUMETSAT, by comparison with the coastal, high-resolution SWAN-Kuststrook wave
model from the Deltares RWsOS North Sea operational forecasting system. This
includes the evaluation of the correlation, the median offset, and the percentage of
cycles with high correlation as a function of distance to the nearest coastline.
Moreover, we analyse the number of valid records and the L2 noise of the records. The
case study comprises five coastal crossings of S6-MF that are located along the Dutch
coast and the German coast along the East Frisian Islands in the North Sea.
We find that the FF-SAR-processed dataset with a Level-1b posting rate of 140 Hz
shows the greatest similarity with the wave model. We achieve a correlation of ~0.8 at
80% of valid records and a gain in precision of up to 29% of FF-SAR vs UF-SAR for 1-
3 km from the coast. FF-SAR shows, for all cycles, a high correlation of greater than or
equal to 0.8 for 1-3 km from the coast. We estimate the decay of SWH from offshore at
30 km to up to 1 km from the coast to amount to 26.4%+-3.1%.
How to cite: Passaro, M., Schlembach, F., Ehlers, F., Kleinherenbrink, M., Dettmering, D., Seitz, F., and Slobbe, C.: Benefits of fully focused SAR altimetry to coastal wave height estimates: A case study in the North Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5859, https://doi.org/10.5194/egusphere-egu24-5859, 2024.
