Ku- and Ka-band Radar Signatures Of Winter Snow-Covered Sea Ice: Observations from the 2019-2020 MOSAiC International Arctic Drift Expedition

We present the first baseline Ku- and Ka-band radar signatures over winter snow-covered sea ice, acquired during the 2019-2020 MOSAiC Arctic Expedition. The radar signatures were acquired using a surface-based, fully-polarimetric, Ku- and Ka-band radar (KuKa radar) from snow-covered sea ice between October 2019 and February 2020; near-coincident with in situ meteorological and snow and sea ice geophysical property measurements . The KuKa radar operated both in altimeter and scatterometer modes, with their center frequencies mimicking those of presently operational Ku- and Ka-band satellite radar altimeter and scatterometer missions.

Preliminary results demonstrate overall low observed Ku- and Ka-band co-polarized (VV and HH) backscatter variability, throughout the winter season. Overall, Ka-band backscatter is greater than Ku-band backscatter, suggesting greater Ku-band radar signal penetration through the upper snow volume. The Ka-band cross-polarized HV backscatter illustrates greater standard deviation throughout winters up to 12 dB, compared to Ku-band HV (only 4 dB deviation), suggesting stronger Ka-band snow volume/multiple scattering, owing to geophysical (snow accumulation/erosion) and thermodynamic (warming events) changes. This is illustrated through a storm/warming event between November 10 and 16, 2019, where substantial warm air intrusion caused significant changes in the snow surface topography and snow metamorphism. This lead to an ~10 dB increase in the Ka-band VV and HH backscatter, especially at nadir- and near-range incidence angles up to 5°, with associated changes in derived polarimetric parameters. Through detailed microwave modeling, we also illustrate the sensitivity of the KuKa radar backscatter to temporal changes in meteorological and snow/sea ice geophysical conditions, throughout the winter season.

Observations from the KuKa radar will provide with the detailed insight and improve our understanding of how snow and sea ice geophysical properties and its associated changes influence the accuracy of satellite-based retrievals of snow depth, sea ice thickness and other critical state variables (e.g. freeze-up and melt-onset timings), from operational and upcoming missions such as SARAL/AltiKa CryoSat-2, Sentinel-3A, SARAL/ALtiKa, CRISTAL, etc.