The Arctic Ocean Observation Operator for 6.9 GHz (ARC3O) - Part 1: How to obtain sea-ice brightness temperatures at 6.9 GHz from climate model output

• Published in: The Cryosphere
• Main Authors: Burgard, C., Notz, D., Pedersen, L., Tonboe, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: Arctic; Arctic Ocean; Sea ice; The Cryosphere
• Online Access: http://hdl.handle.net/21.11116/0000-0005-D492-6; http://hdl.handle.net/21.11116/0000-0006-DFC4-2; http://hdl.handle.net/21.11116/0000-0006-E324-1

We explore the feasibility of an observation operator producing passive microwave brightness temperatures for sea ice at a frequency of 6.9 GHz. We investigate the influence of simplifying assumptions for the representation of sea-ice vertical properties on the simulation of microwave brightness temperatures. We do so in a one-dimensional setup, using a complex 1D thermodynamic sea-ice model and a 1D microwave emission model. We find that realistic brightness temperatures can be simulated in winter from a simplified linear temperature profile and a self-similar salinity profile in the ice. These realistic brightness temperatures can be obtained based on profiles interpolated to as few as five layers. Most of the uncertainty resulting from the simplifications is introduced by the simplification of the salinity profiles. In summer, the simplified salinity profile leads to too high liquid water fractions at the surface. To overcome this limitation, we suggest using a constant brightness temperature for the ice during summer and to treat melt ponds as water surfaces. Finally, in our setup, we cannot assess the effect of snow properties during melting. As periods of melting snow with intermediate moisture content typically last for less than a month, our approach allows one to estimate reasonable brightness temperatures at 6.9 GHz from climate model output for about 11 months throughout the year.