Microwave emission modeling

The relation between brightness temperatures at 1.4 GHz and ice thickness as modeled using MEMLS (dots). The fitted empirical relation from SMOS observed brightness temperatures to ice thickness is in purple borders (Huntemann et al. 2014) and the mean of modeled values at a given thickness is shown with black borders. The input for the emission model was generated using a thermodynamic ice growth model.

The interaction of sea ice with microwave radiation is an important topic for the observation of several sea ice properties throughout the year. Microwave emission modeling has the aim of predicting what a passive microwave sensor onboard satellite or ground-based would see when observing sea ice.

Different mechanisms and structural parameters determine the microwave emission. Firstly any liquid like brine inclusion in the sea ice has a strong interaction with electromagnetic radiation in the microwave regime. Therefore the fraction of liquid, and the geometry of the liquid inclusions in the ice determine the absorption and emission properties. The longer the wavelength (the higher the frequency) the more volume scattering occurs in the ice and snow. These lead to depolarizing effects which again can be predicted using a microwave emission model.

Among the popular Microwave Emission Model of Layered Snow-packs (MEMLS, Wiesmann and Mätzler, 1999) we operate other specialized models for determining the emitted radiation of sea ice. This work is mainly for support of products like the thin ice thickness from the Soil Moisture and Ocean Salinity satellite (SMOS) and the research on determination of snow thickness exploiting multiple frequencies of the AMSR-E and AMSR2 satellite based instruments.





Thermodynamic ice growth

Example of modeled sea ice growth driven by ERA-40 reanalysis data. Temperature evolution of sea ice and snow cover over time. The three 2d plots show the temperature (red) and salinity (blue) profiles for the corresponding location marked on the time axis.

The formation process of sea ice in the arctic ocean is rather complex. Sea ice forms at a lower temperature compared to fresh water ice because of its higher salinity. As the salts do not fit into the crystal structure of fresh water ice, they remain liquid and precipitate only at much lower temperature. This causes a variable liquid brine content in the ice which is essential for the modeling of the interaction of sea ice with electromagnetic radiation especially in the microwave regime (see above).

The thermodynamic model we are using is an extension of the snow accumulation and densification model CROCUS (Brun et al., 1989, Tonboe et al. 2011) and can be driven by atmospheric parameters from ECMWF ERA Interim, JRA-55 or NCEP reanalysis data. The model contains different mechanisms relevant for ice and snow evolution, such as densification, dynamic heat conduction and a parameterization for desalination of the growing sea ice. At the current state the model is especially designed for the freeze-up period and does not include melt processes.