Comparing Altimetry with Tide Gauges and Argo Profiling Floats for Data Quality Assessment and Mean Sea Level Studies

Abstract

Altimeter missions have provided accurate measurements of sea surface height since 1992 not only with TOPEX/Poseidon but also with Jason-1, Envisat, and recently Jason-2. The overall quality assessment of altimeter data can be performed by analyzing their internal consistency and the cross-comparison between all missions. In this study, in situ measurements are used as an external, independent reference to enable further quality assessment of the altimeter sea level. The most up-to-date altimeter data are assessed and compared with those from tide gauges and Argo profiling floats. The first focus is on detection of global and regional drifts in altimeter sea surface height compared with in situ measurements. A second point is that the method can assess the impact of new altimeter standards (e.g., orbit solution, instrumental correction, retracking algorithm) thanks to in situ observations. Finally, the study shows how multiple and reliable altimeter products are used to detect potential anomalies in tide gauges. The results demonstrate the close link between these three steps of the method: while the detection of altimeter drifts using in situ measurements is corrected by computing new altimeter standards whose impact can then be estimated, the improved altimeter sea level time series are used as input for controlling the quality of in situ observations.

Keywords:

• Altimetry
• insitu
• TOPEX/Poseidon
• Jason-1
• Jason-2
• Envisat
• tide gauges
• Argo
• Mean Sea Level
• data quality

Acknowledgements

The tide gauge measurements are collected from the university of Hawaii sea level center (http://www.soest.hawaii.edu/UHSLC). Argo data are collected and made freely available by the international Argo project (a pilot program of the Global Ocean Observing System) and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org).

This activity is supported by CNES in the framework of the SALP contract for all altimeter missions and by ESA within the framework of the Envisat space mission. Part of this study is based on the results from the ESA Climate Change Initiative (CCI) project (http://www.esa-sealevel-cci.org).