On the statistical relationship between sea ice freeboard and C-band microwave backscatter – a case study with Sentinel-1 and Operation IceBridge

Abstract. In this study, we evaluate the statistical relationship between sea ice freeboard and C-band microwave backscatter. By collocating observations between Sentinel-1 images and Operation IceBridge (OIB) measurements in April 2019, we evaluate their relationship under various sea ice types and thickness regimes. We show that, at various spatial scales relevant to synthetic aperture radar (SAR) observations, there exists an apparent significant correlation between C-band backscatter and sea ice freeboard. This relation depends on physical parameters of the sea ice, including the ice type, as well as sensor-specific parameters such as the observational incidence angle of the SAR satellite. As a result, there is considerable variability in this apparent relationship and its fitted parameters. Using the fitted relationship, two-dimensional freeboard maps can be predicted at the scale of SAR images' effective resolution (i.e., ∼ 200 m). More importantly, we demonstrate that although the resolution of SAR images are relatively lower than OIB freeboard maps, we can predict the high-resolution, meter-scale freeboard distribution where altimetry measurements are not available. Thus the representation of altimetric measurements can be improved with the upscaling based on the SAR image. The proposed method can be further utilized for the upscaling of satellite based sea ice topography measurements by the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2). Related issues, including the limitation to spring data, scale dependency and the locality of the statistical relationship, as well as the upscaling of current and historical satellite campaigns, are further discussed.