Estimation and impact of Sentinel-3a GMSL drift on climate-driven studies
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Science I: Climate data records for understanding the causes of global and regional sea level variability and change
Presentation type: Type Oral
Contribution: PDF file
To date, satellite altimetry missions provide a more than 25 years record of continuous measurements of sea level with a very good accuracy. All GMSL groups report very similar results with GMSL trend estimates close to 3.3-3.4 mm/yr over the 1993-2018 period, with an uncertainty of 0.4 mm/yr within a 90% confidence interval (CL). A significant GMSL acceleration over the 25-year period at 0.12 ±0.07 mm/yr² (90% CL) has also been highlighted. Thanks to the good accuracy of altimeter data records, closure budget analyses have been carried out over the past years allowing a better understanding of sea level rise causes.
In order to continue to conduct and enhance these climate-driven studies, altimeter errors should be regularly checked, analyzed and corrected. One of the classical way to do it, it’s to cross compare altimeter missions together in order to detect any jump or drift.
In this study, we are precisely interested in the Sentinel-3a (S3-a) mission launched in February 2016. Indeed, an instrumental drift has recently been detected on S3-a data that have an impact on SWH and range estimates. Although the causes of this drift are still being investigated, preliminary analyses tend to reveal a drift in the width of the System Aperture Radar (SAR) point target response.
This study aims to characterize this S3-a instrumental drift on the evolution of Global Mean Sea Level (GMSL) by comparing with other altimeter missions on the same period (SARAL/Altika, Jason-3 and Jason-2), but also with independent measurements derived from the global tide gauge network. As the S3-a period is short (~3 years), the statistics relevance of the results obtained is analyzed by estimating the uncertainty trend estimates for GMSL altimeter time series separately, but also between two GMSL time series. We also evaluate the impact of different altimeter corrections on S3-a (e.g. empirical corrections, new retracking…).
Finally, through all these analyses, recommendations for improving the S3-a data are made identifying the risks on the different climate-driven studies that need to use these data, especially in the event of Jason-3 failure and also with the perspective of the future Sentinel-6a (Jason-CS) mission. In order to support discussions, we provide an updated altimeter GMSL error budget using Sentinel-3a data instead of Jason-3.