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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.

<link fileadmin images news mod_actus news_insitu_tg_tp.png download>	<link fileadmin images news mod_actus news_insitu_tg_j1.png download>	<link fileadmin images news mod_actus news_insitu_tg_en.png download>
Comparisons in cm between altimetry and tide gauges in terms of drifts for TOPEX/Poseidon (left), Jason-1 (middle) and Envisat (right) for the corresponding periods. Credits CLS/Cnes/Esa.

• The  difference between Jason-1 and Envisat in terms of trends is consistent to what is observed with the global MSL as described <link internal-link-new-window>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 (<link internal-link>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.

<link fileadmin images news mod_actus news_insitu_argo_j1.png download>	<link fileadmin images news mod_actus news_insitu_argo_en.png download>
Comparisons in cm between altimetry and ARGO T/S  in terms of drifts for Jason-1 (left) and Envisat (right) for the East (0-180°) and West (180-360°) areas. Credits CLS/Cnes/Esa.

Further information:

• <link internal-link-new-window>Systematic Validation activties
• <link fileadmin documents calval validation_report insitu annual_report_insitu_2010.pdf download>Annual validation report for comparisons between altimetry and tide gauges 2010
• <link fileadmin documents calval validation_report insitu annual_report_insitu_ts_2010.pdf download>Annual validation report for comparison between altimetry and ARGO T/S profiles 2010
• <link internal-link-new-window>Mean Sea Level Rise
• <link internal-link-new-window>In-situ tide gauges global statistics