Interpretation of polarisation behaviour of radar waves transmitted though Antarctic ice shelves

We have collected polarimetric ice sounding radar data on Brunt, George VI and Ronne ice shelves using a vector network analyser as a continuous wave step-frequency radar. Being a wideband phase sensitive instrument, the radar allowed the vectorial nature of the interaction between radio waves and the ice and reflecting surface to be explored. Single crystals of ice are birefringent not only at optical frequencies but also at radar ones, so in an ice sheet the average crystal orientation fabric determines the overall level of birefringence. The polarisation of radio waves is changed by the birefringent nature of the ice and by the reflecting surface, whether an internal layer or the basal boundary. By transmitting and receiving on orthogonal linearly polarised aerials, we could use a scattering matrix approach to determine parameters related to the physical properties and nature of both the ice and the reflecting surface. The polarisation behaviour will have to be allowed for when processing ice penetrating SAR data.