Diurnal Change from Surface to Volume Scattering Induced by Thaw and Refreeze of the the Snow Cover: a Thermodynamic Approach

Sea ice morphological features are of major relevance to oceanic and general circulation models as well as navigation or oil and gas exploration [1]. Beside their first order impact on drag coefficients [2], they create a horizontal heterogeneity of the dynamic and therefore thermodynamic conditions at the ice water interface which control ocean-ice-atmosphere fluxes. However, computer limitations preventing the resolution of boundary layer processes with two roughness scales and unavailability of adequate data sets regarding the roughness variability and more specifically ridge distribution [3] [4] over an ice field prevent the integration of these properties of the sea ice cover into large scale models. Synphetic Aperture Radars (SAR) with improved resolutions, up to 3 meters in the ultra-fine-mode of RADARSAT-2, and the independence of microwaves from cloudy conditions often encountered in polar areas, offer the potential tools to better describe the statistics of large roughness features at scales compatible with large scale models [5] [6] [7]. Whereas most morphological features are satisfactorily extracted from images throughout the winter season, the contrast between the ridge network and the un-deformed sea ice sheet is at its maximum during the melt season. At spring, the increase of the water content in the snow makes it opaque to microwaves and, in turn, causes surface scattering to be the main contribution of radar images. As a consequence, the radar signal becomes mainly function of the surface small scale roughness and interface slope. The angular dependence of surface scattering creates conditions allowing a higher return from ice blocks with a surface oriented perpendicularly to the SAR incident beam and on the contrary a reduced backscattering from other areas within the scene where forward scattering causes the beam energy to be scattered away from the antenna.