CryoSat Cal/Val – Accuracy and Penetration Depth of the CryoSat SARIn product

Abstract

CryoSat-2 was launched in April 2010, as part of the European Space agency's (ESA) Earth Opportunity Programmes. The primary scientific objectives of the mission are to determine changes of the ice sheet elevation and sea ice thickness within its nominal lifetime of five years to get a better understanding of the short-term response of the Cryosphere to climate change. In order to validate the scientific data products four post-launch CryoSat Calibration/Validation Experiments (CryoVEx) were carried out since CryoSat-2’s successful launch. The CryoVEx campaigns included co-coordinated field and airborne measurements at selected validation sites in the Arctic and Antarctica. We will present first results of CryoSat-2 comparisons with GPS data acquired at the Halvfarryggen ice dome in Dronning-Maud-Land (DML), Antarctica during CryoVExANT-2010. A second comparison will be shown with airborne laser scanner data acquired during the same campaign in the Blue Ice area next to Novo runway also situated in DML. The GPS and laser scanner data will be used as reference elevation for the analysis. For our comparisons, we use CryoSat-2 level 1b and level 2 data products acquired in the SARIn mode, since the validation sites are close to the coast with surface slopes of up to one degree. Both sites have different snow/firn properties, which can be used to determine the penetration depth of the Ku-Band signal. The area around Halvfarryggen is characterised by a strong east-west gradient in snow accumulation rate, ranging from 0.5 m to 3 m firn per year. The Novo area is pure Blue Ice, covered with small patches of snow. Therefore, different backscatter mechanism will dominate the received radar signal, volume scattering at the Halvfarryggen and surface scattering in the Blue Ice area, respectively. For volume scattering, the re-tracked surface elevation is typically biased with the effective penetration depth of the radar signal. In the Blue Ice area no signal penetration is expected and the re-tracked radar elevation should resemble the GPS determined surface elevation. Apart from results with respect to penetration depth, we will get a first estimate of the accuracy of the CryoSat-2 SARIn product using interferometric phase processing which accounts for across track slopes