The coastal performance of SAR altimetry from CryoSat-2 and Sentinel-3
Event: 2016 SAR Altimetry Workshop
Session: SAR mode performances: SAR CALVAL from Cryosat-2 and Sentinel-3
Presentation type: Type Oral
SAR altimetry is expected to be particularly advantageous in the coastal zone, due to the much higher along-track resolution and the better signal to noise ratio of the SAR mode. This is confirmed by the results of an assessment of the performance of SAR altimetry around the coast of the UK using CryoSat-2 data and Sentinel-3 data, which we show in this contribution. This assessment has been carried out within the ESA-funded CryoSat Plus for Oceans Project (CP4O) and SCOOP projects. The diagnostic that we use as a measure of the instrumental noise is the absolute value of the difference amongst consecutive 20-hz samples, both for height and significant wave height. Results demonstrate that in favourable conditions at 2 km from the coast we get the same level of noise as over the open ocean, i.e. less than 5 cm noise for the 20-Hz data for SSH, and less than 45 cm noise for the Significant Wave Height, and noise figures at 1 km are only slightly greater if some screening based on waveform fitting is carried out. Specific processing configuration (Hamming filter in azimuth, pre-FFT zero padding) improves the noise characteristics. Validation of SSH against tide gauges is encouraging: with fine tuning of search radius (and sometimes outlier removal) we can get RMS < 10 cm with search radii ~20 km. We also demonstrate the important potential for SAR altimetry to help characterise the wave field close to the coast– with examples of sheltering of the waves in areas of complex morphology, and shoaling effects in areas where the coast is simple and the tracks are nearly orthogonal to the coastline, such as the region along the UK south coast close to Brighton.