CoAuthors

Ernst Schrama (TUDelft, Netherlands); Remko Scharroo (EUMETSAT, Germany)

CryoSat-2, in orbit since April 2010, observes the cryosphere with an innovative altimeter system capable of conventional (LRM) and delayed-Doppler (SAR) altimetry. In addition to sea ice freeboard and ice sheet elevation change, the SIRAL altimeter onboard CryoSat-2 perfectly samples the global ocean surface and all its dynamics. We present results of the CryoSat-2 LRM and pseudo-LRM (reduced SAR) calibration and validation efforts in frame of the ESA GOP/IOP/FDM project. To be able to exploit the data to the fullest it is necessary to assess, validate and improve them where possible. Up to now we have been complementing the Radar Altimeter Database System RADS with an improved dataset (based on NOAA retracker) not just for the sake of altimeter database completeness but also for using CrySat-2 data as climate data record (CDR) and for improving sampling resolution in combined altimetry solutions from different missions. We have validated the LRM data, added and improved corrections, added pseudo-LRM (compressed/reduced SAR) to complement the global coverage, and verified the orbit accuracy. The present status of the absolute and relative calibration of LRM data is discussed, also by comparison and evaluation with ESA’s CryoSat-2 GOP/IOP/FDM, with other concurrent altimeter satellites by crossover analyses and with in-situ data from selected tide gauges. Partly based on these results ESA intends to upgrade its processing chain in 2016. The enclosed figure shows the SSA from CryoSat-2 (left) and from JASON-2 (right) data. The (mesoscale) variations compare very well, only an apparent relative bias between the two of around 4 cm remains.

In addition we reviewed the combined capacity of Cryosat-2 and SARAL altimeter data data to reestablish the altimetric mesoscale variability measuring capability from before the demise of Envisat and Jason-1. For this we also validate and monitor the data from the Altika instrument onboard SARAL, which was launched in 2013 to carry the first Ka-band altimeter.