Sea Ice Emissivity Modeling at L-Band and Application to 2007 Pol-Ice Campaign Field Data

Sea ice emissivity models for the L-band frequency range are described and then tested on Pol-Ice campaign field measurements. Pol-Ice was conducted in March 2007 in the Northern Baltic in preparation for the launch of the Soil Moisture and Ocean Salinity (SMOS) instrument, a satellite microwave radiometer operating at 1.4 GHz. The campaign comprised airborne measurements from the EMIRAD L-band radiometer and the E-M Bird ice thickness meter. Because of the translucency of sea ice at L-band, it is hoped that SMOS will render information on ice thickness. Three variations on radiative transfer are used to model EMIRAD brightness temperatures from collocated E-M Bird measurements: a single plane-parallel model, an ensemble of such models, and a ridged Monte Carlo model based on geometric optics that includes both the top- and bottom-surface topography. All three models accurately account for the instrument antenna pattern, relevant to satellite-mounted radiometers that sample a large and heterogeneous area. Because of ice growth processes, salinity and, by extension, permittivity are partial functions of ice thickness; thus, the models are further refined so that permittivity varies with ice thickness, which was necessary to correctly model the polarization difference. Other issues related to effective permittivities, an intermediate quantity in the models, are discussed. Analysis of partial correlations shows that ice ridging makes a significant contribution to the measured signal, commending further study using scattering models that are more appropriate to the scale of the ridging relative to the wavelength.