Cryosat-2 Calibration and Validation Results
Naeije, Marc1; Schrama, Ernst1; Scharroo, Remko2; Yi, Yuchan3; Visser, Pieter1
1TUDelft, NETHERLANDS; 2NOAA/Altimetrics, UNITED STATES; 3School of Earth Sciences/OSU, UNITED STATES

CryoSat-2 was successfully launched in April 2010 to map the cryosphere with an advanced microwave altimeter system, including SAR and SARin capabilities. The mission goal is to observe sea ice freeboard and ice sheet elevation changes for a nominal period of 3 years. Precision orbit determination (POD) of CryoSat-2 relies on DORIS Doppler tracking and ground based satellite laser ranging (SLR). Here we show an update on the results of our CryoSat-2 POD efforts. The Delft orbits compare well with the MOE and POE trajectories computed by CNES and can be considered of Jason-class. We find RMS of SLR residuals around 2cm and RMS of radial differences around 1.5cm when compared to the CNES POE orbits. We address data sources, availability, latency, quality and editing, software, standards and methods and focus the discussion on possibilities to further improve the orbit, e.g. by the use of a dedicated satellite macro model.

Then, we also show an update on the results of our CryoSat-2 LRM CAL/VAL efforts. The SIRAL altimeter onboard CryoSat-2 perfectly samples the ocean surface. To be able to exploit these data it is necessary to assess and validate them. Another reason is that we want to to complement the Radar Altimeter Database System RADS with this dataset to improve the combined altimeter sampling resolution both in time and space. This has become very pressing, now Envisat stopped providing data and meanwhile its successor Sentinel-3 is not yet in place. 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), and verify the orbit accuracy. The present status of the absolute and relative calibration of LRM Level-2 data is discussed, also by comparison of CryoSat-2 with other satellites (crossover and grid analyses) and with tide gauge data. We provide estimates on range and timing biases and try to explain them. In this update of CAL/VAL results we focus on the latest ESA version of the product and compare with our own efforts to improve the ocean product.