CryoSat Ice Baseline-D Validation and Evolutions

• Main Authors: Meloni, Marco, Bouffard, Jerome, Parrinello, Tommaso, Dawson, Geoffrey, Garnier, Florent, Helm, Veit, Bella, Alessandro, Hendricks, Stefan, Ricker, Robert, Webb, Erica, Wright, Ben, Nielsen, Karina, Lee, Sanggyun, Passaro, Marcello, Scagliola, Michele, Bjerregaard Simonsen, Sebastian, Sandberg Sørensen, Louise, Brockley, David, Baker, Steven, Fleury, Sara, Bamber, Jonathan, Maestri, Luca, Skourup, Henriette, Forsberg, René, Mizzi, Loretta
• Format: Text
• Language: English
• Published: 2019
• Subjects: Austfonna; Ice cap; Sea ice
• Online Access: https://doi.org/10.5194/tc-2019-250; https://www.the-cryosphere-discuss.net/tc-2019-250/

The ESA Earth Explorer CryoSat-2 was launched on 8 April 2010 to monitor the precise changes in the thickness of terrestrial ice sheets and marine floating ice. For that, CryoSat orbits the planet at an altitude of around 720 km with a retrograde orbit inclination of 92° and a <q>quasi</q> repeat cycle of 369 days (30 days sub-cycle). To reach the mission goals, the CryoSat products have to meet the highest quality standards to date, achieved through continual improvements of the operational processing chains. The new CryoSat Ice Baseline-D, in operation since 27th May 2019, represents a major processor upgrade with respect to the previous Ice Baseline-C. Over land ice the new Baseline-D provides better results with respect to previous baseline when comparing the data to a reference elevation model over the Austfonna ice cap region, improving the ascending and descending crossover statistics from 1.9 m to 0.1 m. The improved processing of the star tracker measurements implemented in Baseline-D has led to a reduction of the standard deviation of the point-to-point comparison with the previous star tracker processing method implemented in Baseline-C from 3.8 m to 3.7 m. Over sea ice, the Baseline-D improves the quality of the retrieved heights in areas up to ~ 12 km inside the Synthetic Aperture Radar Interferometric (SARIn or SIN) acquisition mask, which is beneficial not only for freeboard retrieval, but for any application that exploits the phase information from SARIn Level-1 (L1) products. In addition, scatter comparisons with the Beaufort Gyre Exploration Project (BGEP, https://www.whoi.edu/beaufortgyre ) and Operation IceBridge (OIB, Kurtz et al., 2013) in-situ measurements confirm the improvements in the Baseline-D freeboard product quality. Relative to OIB, the Baseline-D freeboard mean bias is reduced by about 8 cm, which roughly corresponds to a 60 % decrease with respect to Baseline-C. The BGEP data indicate a similar tendency with a mean draft bias lowered from 0.85 m to −0.14 m. For the two in-situ datasets, the Root Mean Square Deviation (RMSD) is also well reduced from 14 cm to 11 cm for OIB and with a factor 2 for BGEP. Observations over inland waters, show a slight increase in the percentage of <q>good observations</q> in Baseline-D, generally around 5–10 % for most lakes. This paper provides an overview of the new Level-1 and Level-2 (L2) CryoSat ice Baseline-D evolutions and related data quality assessment, based on results obtained from analysing the 6-month Baseline-D test dataset released to CryoSat expert users prior the final transfer to operations.