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Those documents present the synthesis of the comparisons of two kinds of in-situ measurements with Sea Surface Height altimetry: tide gauges and ARGO T/S profiles.

Both studies allow to
1. Monitor the SSH between altimeter and external independent in-situ measurements in order to detect potential drifts or jumps in the altimeter Mean Sea Level (MSL)
2. Estimate the improvements performed on the new altimeter standards in the SSH calculation
3. Detect the potential anomalies of the computed in-situ datasets

FOCUS ON TIDE GAUGE COMPARISONS:

• The drifts estimated for Jason-1 and TOPEX/Poseidon have been respectively estimated to 0.27 mm/year and 0.7 mm/year , within the error of the method (+/- 0.5 mm/yr). The stronger drift for T/P is due to a poorer precision of the TOPEX A altimeter at the beginning of the mission. For Envisat the estimation is -1.7 mm/yr with a stronger error because of the East/West discrepancies of the orbit.

• The  difference between Jason-1 and Envisat in terms of trends is consistent to what is observed with the global MSL as described here.

• This activity also leads to the realisation of individual comparison between altimetry and tide gauges.

FOCUS ON ARGO T/S COMPARISONS:

• The map of the MSL trends differences between Jason-1 and Envisat has revealed a strong anomaly of East / West (longitudes 0°/180° and 180°/360°) MSL discrepancy (see calval overview). This year, the comparison of Jason-1 and Envisat altimeter measurements with ARGO data has enabled us to associate this anomaly to the Envisat mission, probably in relation with the orbit determination. Indeed, the slope difference between East and West hemispheres is of 5.7 mm/y for Envisat whereas it is reduced at 1.9 mm/y for Jason-1.

Further information:

• Systematic Validation activties
• Annual validation report for comparisons between altimetry and tide gauges 2010
• Annual validation report for comparison between altimetry and ARGO T/S profiles 2010
• Mean Sea Level Rise
• In-situ tide gauges global statistics