Recent Cryosat-2 and SARAL calibration and validation results

Marc Naeije (TUDelft, Netherlands)


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

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Regional and Global CAL/VAL for Assembling a Climate Data Record

Presentation type: Type Poster

CryoSat-2, in orbit since April 2010, maps the cryosphere with a dedicated altimeter system capable of LRM altimetry, SAR and SARin. It already surpassed its nominal 3 year mission of observing the sea ice freeboard and ice sheet elevation change. In addition to ice, the SIRAL altimeter onboard CryoSat-2 perfectly samples the global ocean surface, predominantly in LRM mode but also in SAR mode. We show an update of the results of the CryoSat-2 LRM and pseudo-LRM (reduced SAR) calibration and validation efforts. To be able to exploit these data to the fullest it is necessary to assess, validate and improve them. Up to now we have been complementing the Radar Altimeter Database System RADS with this improved dataset, not only for the sake of completeness but also for being able to use the CrySat-2 data as climate data record (CDR) and for improving the combined altimeter sampling resolution both in time and space. So, we validate and calibrate the LRM data, add and improve corrections (including modeling of corrections that are not directly available from the CryoSat-2 platform), add pseudo-LRM (compressed SAR) to complement the global coverage, and verify the orbit accuracy. The present status of the absolute and relative calibration of LRM data is discussed, also by comparison of CryoSat-2 with other satellites (crossover analyses) and with tide gauge data. We focus on the latest ESA version of the ocean product and compare that with our own efforts to improve the product, which incorporates re-tracking of the wave forms and the determination of a dedicated sea state model. In addition we review the capacity of Cryosat-2 and recent 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 calibrate and validate the data from the Altika instrument onboard SARAL. SARAL was launched in 2013 and carries the first Ka-band altimeter.
Marc Naeije