Our understanding of snow distribution in the polar regions is severely restricted owing to the heterogeneity, both in space and time, of this solid precipitate. Processes such as vapor and mass fluxes across the interface are, to a large extent, controlled by the presence and geophysical state of the snow cover on sea ice. Numerous studies have shown the importance of snow cover in ecosystem processes and particularly in photosynthetically active radiation extinction. Researchers are currently exploiting developments in electromagnetic interaction theory in an attempt to measure snow thickness distributions remotely. In this paper, we investigate the dependence of radar backscatter on snow thickness over smooth first-year ice. We use data from the Seasonal Sea Ice Monitoring and Modeling Site located in the Canadian Archipelago. Results show that the thermodynamics of the snow cover affect wave propagation, attenuation, and scattering through the control that brine volume exerts on interfacial characteristics of the snow and ice layers. The effect is subtle and specific to certain ranges of salinity, surface roughness and thickness of sea ice. We describe the phenomenon responsible for this effect using a microwave model consistently for both complex effective permittivities and backscatter coefficients coupled to a one-dimensional model. We validate the physical principles using in situ field data. We then discuss the potential of synthetic aperture radar in estimating snow thickness distributions under these specific conditions using both observed and modeled microwave scattering. ¿ 1999 American Geophysical Union