Analyses of Altimetry Errors Using in-situ Measurements: Tide Gauges and Argo Profiles
Ablain, Michaël¹; Valladeau, Guillaume¹; Legeaos, Jean-François¹; Prandi, Pierre¹; Picot, Nicolas²; Femenias, Pierre³; Benveniste, Jerôme^3
1CLS, FRANCE; ²CNES, FRANCE; ³ESA/Esrin, ITALY

Altimeter missions provide accurate measurements of sea surface height from 1992 onwards. The global quality assessment of altimeter data is usually performed by the analysis of their internal consistency and the cross-comparison between all missions. In this study, in-situ measurements are used as a complementary approach to analyze the altimetry errors, especially for climate scales. Two types of in situ measurements are used:tide gauges and Argo profiles. Tide gauge data derived from several networks (GLOSS/CLIVAR, PSMSL,...) provide sea-level heights with a physical content comparable with altimetry sea level estimations. They also cover the whole altimetric period but only on coastal areas. Therefore, Argo profiling floats are complementary data since they are more evenly spread out in the open ocean, but with enough spatial coverage since 2004 only. However they measured the temperature and salinity vertical profiles, providing only the steric contribution of to the total sea level content measured by altimeters. The mass contribution derived from the GRACE dataset from 2003 onwards is thus also used and is derived from the GRACE dataset from 2003 onwards. In this study, in situ measurements are compared with altimeter sea-level for the main altimeter missions with a focus on ESA missions: Envisat, ERS-1 and ERS-2 but also CryoSat. If altimeter time series are long enough, tide gauge data provide a relevant estimation of the global Mean Sea Level (MSL) drift calculated for all the missions. Argo profiles are able to detect MSL drifts at basin scales thanks to the better ocean coverage. Correlation, variance differences between altimeter and in-situ sea level are also estimated accurately, separating the temporal scales (high, medium, low frequencies). Comparison with sea level products merging all the altimeter missions together have also been performed using AVISO (delayed-time Sea Level Anomaly grids) and the Sea level Climate Change Initiative (SL-CCI) datasets.