Scattering from Snow Backgrounds at 35, 98, and 140 GHz.

• Main Authors: Hayes,D T, Lammers,U H W, Marr,R A
• Other Authors: ROME AIR DEVELOPMENT CENTER GRIFFISS AFB NY
• Format: Text
• Language: English
• Published: 1984
• Subjects: Snow; Ice and Permafrost; Radiofrequency Wave Propagation; *BACKSCATTERING; *SNOW; *SNOW COVER; MILLIMETER WAVES; TERRAIN; DEPTH; ANTENNAS; CROSS POLARIZATION; Antenna footprints; WURADC46001607; PE62702F; Ice; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA145798; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA145798

Potentially, millimeter wave systems operating near terrain interact strongly with snow cover. The dependence of the millimeter-wave backscatter coefficient on physical snow parameters, such as metamorphic state and free-water content, were explored. The results complement a previous study done on dry slabs removed from snow cover (RADC-TR-81-88). Low-power cw scatterometers at frequencies of 35, 98, and 140 GHz allowed backscatter measurements on in-situ snow at vertical, horizontal, and crossed polarization. Backscatter coefficients reported here were obtained by averaging returns while the scatterometer antenna footprints swept over the snow in a continuous circular motion. Grazing angles on the surface, constant during a sweep, were parametrically changed from 90 deg to 45 deg to 15 deg. The measurements took place in march 1978, late during that winter, when the snow cover was usually melting during the day and refreezing during the night. Melting-water calorimetry provided the free-water data. The snow depth on the ground exceeded 30 cm. It was composed of layers ranging from fresh to almost month-old granular snow. Like-polarized backscatter coefficients of dry in-situ snow spread from a minimum of -12 dB at 35 GHz and 15-deg grazing angle to wellover 0 dB at all frequencies (8 dB at 140 GHz) at 90-deg grazing angle. The cross-polarized backscatter coefficient, following the same trend, ranged from a low of -16 dB at 35 GHz and 15 deg to a high of 4 dB at 140 GHz and 90 deg.