Since 1995 at CLS, cross calibration activities have been developed for the needs of comparison between ERS-1 and Topex/Poseidon (TP) instruments and combination of altimeter data. On one hand, inter calibration supports calibration and validation activities (CalVal), for systematic and long term monitoring of the discrepancies between missions. In addition, this intercalibration activity allows updating data on a regular basis in order to generate homogeneous and efficient altimetric products. With other altimetry satellite missions, these activities have grown and now concern the cross calibration among ERS-2, Envisat, Topex/Poseidon, Jason-1, GFO.

CLS tasks:

For the needs of calibration and validation (CalVal), it is necessary to compare the measurements of the different missions. This comparison is done along-track for tandem missions (Envisat/ERS-2 and of Jason-1/TP in the beginning of Jason-1), or at crossovers for the cross calibration of ERS-2/TP, Envisat/Jason-1, ERS-2/Jason-1. In the two cases, cyclic maps are drawn and cyclic and daily monitoring are processed to control instrumental drifts.

An adjustment method has been developed, to provide a reference for all the missions and to correct for the long-wavelength errors on missions like ERS-2, GFO or Envisat.

Updating afterwards the data sets with the most recent corrections lead to create high-performance products. This is another aim of the cross calibration. Those products are available to the oceanographic community as well as for the computation of oceanographic mean sea surfaces and the monitoring of mean sea level. (See Ssalto/Duacs and CalVal brochures.)

Users:

Results from validation and studies on data quality are disseminated to Cnes and Esa users along with data products.

More:

• Topex/Poseidon and Jason-1, Aviso web site: http://www.jason.oceanobs.com
• Envisat, Esa web site: http://envisat.esa.int/calval/
• ERS, Ifremer web site: http://www.ifremer.fr/cersat/