Millimeter wave backscattering experiments in arctic winter

Millimeter wave sky backscattering in arctic winter conditions close to ground level is not dominated by snowfall. Preliminary measurements at Ka and V-bands suggest that average equivalent backscattering areas stay around 1-3 m/sup 2/ also during wet snowing for both linear polarizations. Sudden high values of backscattering are observed in temperatures below -30 degrees. Successive meteorological inversion layers seem to cause backscattering areas above 10 m/sup 2/ in otherwise similar test conditions. The process can last 3-4 hours. Requirements for such phenomena are steep vertical temperature and humidity profiles, which may exceed 20 degrees and 20 per cent for 200 meters, respectively. Some of these measurements have been performed with a portable 10 mW bistatic system. The receiver noise floor is about -90 dBm. Different antennas are used according to frequency, spatial resolution and desired illumination, including horns supplemented by dielectric lenses. Their gain varies from 19 to 40 dBi. The current synchronization scheme relies on a common X-band IF that is connected through coaxial cable.