Investigation of SMOS Sea Ice Thickness Retrieval with respect to the Ice Temperature Gradient within an Ice Layer

Abstract:

Following the launch of European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite mission, it has been shown that brightness temperatures at a low microwave frequency of 1.4 GHz (about 21 cm wave length) are sensitive to sea ice properties. In contrast to the higher frequencies at which previous microwave sensors have been operated, the radiation over sea ice measured at L-band originates not only from the surface but also from the deeper parts of the ice, thus contains information of sea ice thickness. An iterative retrieval algorithm has been developed, based on a thermodynamic sea ice model and a three-layer radiative transfer model. The algorithm explicitly takes variations of ice temperature and ice salinity into account. Furthermore, ice thickness variations within a SMOS footprint are considered through a statistical thickness distribution function. This algorithm has been used for the continuous operational production of SMOS-based sea ice thickness data set from 2010 on at the University of Hamburg. In the current operational retrieval algorithm, the emissivity model does not correctly account for vertical gradients of ice temperature and salinity. The invalid assumption of a vertically homogeneous ice layer could introduce uncertainties because the relative brine volume and thus the permittivity depends on ice temperature and salinity. A first investigation of the influence of ice temperature gradient on the ice permittivity, and thus the retrieval of SMOS ice thickness will be shown.