Assessment of radar freeboard, radar penetration rate, and snow depth for potential improvements in Arctic sea ice thickness retrieved from CryoSat-2

Abstract

The accuracy of Arctic sea ice thickness retrieved from the CryoSat-2 satellite is significantly influenced by the sea ice surface roughness, snow backscatter, and snow depth. In this study, four updated cases incorporating physical model-based radar freeboard, newly estimated radar penetration rate, and well-validated satellite snow depth were constructed to evaluate their potential improvements to the Alfred Wegener Institute's CryoSat-2 sea ice thickness (AWI CS2). The updated cases were then compared with airborne remotely sensed observations from the National Aeronautics and Space Administration's Operation IceBridge (OIB) and CryoSat Validation Experiment (CryoVEx) in 2013 and 2014, as well as with ground-based observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to April 2020. The results showed that all updated cases had the potential to improve the accuracy of sea ice thickness, maintaining comparable correlation coefficients and significantly reducing statistical errors compared to the AWI CS2. In the evaluation with OIB, CryoVEx, and MOSAiC, the four updated cases reduced the root mean square error of AWI CS2 by up to 0.68 m (55 %) against OIB, 0.76 m (53 %) against CryoVEx, and 0.47 m (76 %) against MOSAiC. The updated sea ice thicknesses retained the main distribution patterns generated by AWI CS2, but generally showed thinner sea ice thicknesses. From 2013 to 2018, the interannual variation trends between the updated cases and AWI CS2 varied regionally, but both show significant decreasing trends along the northern coasts of the Canadian Arctic Archipelago and Greenland. The updated schemes provided new insights into the retrieval of sea ice thickness using CryoSat-2, thereby further contributing to the quantification of the sea ice volume in the context of a warming climate.