Monitoring boreal and arctic freeze/thaw with the first year of SMAP brightness temperatures

The first year of SMAP brightness temperature (TB) time series was analyzed to characterize the response to surface freeze/thaw variations over two sites (northern boreal forest; Arctic tundra) using various in situ air, soil, and snow measurements as reference. The results show that the Normalized Polarization Ratio (NPR) can distinguish the landscape freeze/thaw state. We also provide evidence that a lag in the lake ice break-up compared to thaw of the ground surface can induce a significant variation in TB and NPR values in lake rich areas.