LABORATORY MEASUREMENTS OF RADAR BACKSCATTER FROM BARE AND SNOW-COVERED SALINE ICE SHEETS

We performed experiments to collect radar backscatter data at K-u (13.4 GHz) and C bands (5.3 GHz) over simulated sea ice at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) during the 1990 and 1992 winter seasons. These experiments were conducted over bare saline ice grown in an indoor tank and an outdoor pond facility. The radar data were calibrated using a complex vector calibration scheme to reduce systematic effects. In conjunction with the radar measurements we measured ice physical properties. These measurements demonstrate that the dominant backscatter mechanism for bare saline ice is surface scattering. Both the copolarized and cross-polarized measurements compare favourably with the predictions of surface scattering models at two frequencies. During the 1992 indoor tank experiment we applied four successive layers of snow (about 2.5 cm each) to the saline ice sheet after the ice thickness had reached about 12 cm. The backscatter at normal incidence dropped by 15 dB and the backscatter at 45 degrees increased by 11 dB with the introduction of the first snow layer. The application of three more layers, each of approximately 2.5 cm depth, did not alter the radar signature significantly. By modelling and direct observation we found that the initial change in the signature was caused by a roughening of the surface at the snow-ice interface and the change in dielectric contrast at the snow-ice interface.