Young sea ice signatures in the deep Arctic during the fall freeze-up

The authors performed radar backscatter measurements early in the fall freeze-up as part of the 1991 International Arctic Ocean Expedition (IAOE´91) to investigate the ability of observing and distinguishing between young sea ice types with radar. Measurements were taken at all four linear polarizations (VV, HH, VH, HV) with a C-band FM-CW radar system built at The University of Kansas Radar Systems and Remote Sensing Laboratory (RSL). A number of young ice types were investigated during IAOE´91. These included light nilas, dark nilas, and pancake and slush sea ice types. Monitoring the early stages of sea ice growth is vital because the changing sea ice cover controls the heat exchange between the ocean and air. New ice growth is also responsible for adding brine into the upper portion of the water column. Thin sea ice also significantly affects the albedo of the surface as it changes from a sea surface to an ice surface. These radar measurements indicate that for spaceborne radar sensors such as the ERS-1 SAR and the Canadian RADARSAT SAR to be able to observe dark nilas ice they must be able to measure σ⁰ as low as -30 dB for VV polarization (ERS-1) and -34 dB for HH polarization (RADARSAT). The ERS-1 SAR should be able to observe slightly older sea ice types, such as light nilas and pancake ice, due to the higher backscatter from these ice types. To observe the cross-polarized response of these young ice formations a radar sensor must be capable of measuring σ⁰ values as low as -35 to -50 dB