Validation of Sentinel-3A SAR mode sea level anomalies around the Australian coastal region

Abstract

The Synthetic Aperture Radar (SAR) mode sea level anomalies (SLAs) of Sentinel-3A altimetry mission around the Australian coastal region were validated using eight in situ tide gauge sea level records and retracked Jason-3 datasets from a modified Brown-peaky (MBP) retracker. The MBP is a modified version of our existing Brown-peaky retracker aimed at enhancing BP's performance. We compared the noise of Sentinel-3A SLAs averaged across three posting rates (i.e. 1 Hz, 2 Hz and 4 Hz) with the 1 Hz noise of MBP-derived Jason-3 SLAs. At distances >10 km from the coast, the noise level of 1 Hz Sentinel-3A SLAs (~1.2 cm) is lower than that of the MBP-retracked Jason-3 SLAs (~1.7 cm). Moreover, the noise level of 2 Hz Sentinel-3A SLAs is comparable to that of the 1 Hz MBP-derived Jason-3 dataset, indicating that Sentinel-3A can provide precise SLAs at finer spatial scales. The Root Mean Square Error (RMSE) of differences between the tide gauge SLA time series and the equivalent SLA time series at each along-track altimeter point was used to assess pointwise data quality. For both Sentinel-3A and MBP-retracked Jason-3, the along-track RMSEs of 20 Hz SLAs vary between 0.05 m and 0.2 m. The mean and standard deviation (STD) of 1 Hz SLA differences at crossover points were computed for each individual altimetry mission to assess overall data quality. When compared with the crossover analysis results, the quality of Sentinel-3A SLAs is superior to that of the retracked Jason-3 dataset in terms of smaller STDs at crossover points (8.8 cm vs. 10.7 cm).