Refraction Scattering in the Anomalous Reflections from Icy Surfaces

The modes of scatter at radar targets are discussed and in particular the mode due to internal refraction in the target material whenever a gradual transition in the refractive index occurs. The importance of this arises mainly in planetary radar, as this could account for the unusual polarization effects observed on the icy satellites of the major planets and in certain parts of Mercury and Mars. Ices with their low radar surface reflectivity and low internal absorption would be the best naturally occurring materials to cause these effects. Indeed similar effects have been reported in radar observations over sections of the Greenland ice shelf. The nature of these effects can most easily be seen in the simple approximation of geometrical optics, and a more detailed discussion presented in the applicable electromagnetic theory confirms these results, even when the size of the inclusions is only on the order of a wavelength.