Improving precision of high-rate altimeter sea level anomalies by removing the sea state bias and intra-1-Hz covariant error

Abstract

This paper assessed the precision of 20-Hz sea level anomaly (SLA) estimates with different sea state bias (SSB) corrections from reprocessed Jason-1/2/3 and Sentinel-3A data over the period of 2002–2019 within 100 km from the entire Australian coast. The altimeter waveforms were retracked by the modified Brown-peaky (MBP) retracker for Jason missions and by the SAMOSA+ retracker for Sentinel-3A. We recalculated the 20-Hz and composite SSB corrections using a regional parametric model from 20-Hz retracked estimates of the SLA, significant wave height (SWH) and wind speed. The composite SSB correction, which was recomputed after removing the retracker-dependant correlated error in 20-Hz SLA, is found to achieve better performance than other SSB corrections in the study area. Applying the 20-Hz and composite SSB corrections has reduced ~10% and ~13% of noise, respectively, in the MBP-retracked 20-Hz Jason SLA estimates, while only ~2% of noise reduction is shown by applying the 1-Hz standard SSB correction. It is also found that the improvement of retracked Sentinel-3A SLA estimates by SSB corrections is very low (~3%), indicating a dedicated SSB correction model should be developed for the SAR mode altimeter.As a result, the precision of composite SSB-corrected SLA estimates for all Jason missions can be retained at the level of 5.1 ± 1.1 cm until 3 km from the Australian coast, which is slightly lower than that of Sentinel-3A (4.2 ± 0.9 cm). The degradation within 3 km from the coast mainly corresponds to the along-track direction for MBP-retracked Jason SLA estimates, and the across-track direction for SAMOSA+ retracked Sentinel-3A SLA estimates, respectively.