Eastern Arctic SURSAT SAR Ice Experiment: Radar Signatures of Sea Ice Features

摘要

Evaluation of X- and L-band steep angle synthetic aperture radar (SAR) sea ice imagery taken in Baffin Bay and Davis Strait in April 1979 has shown that description and discrimination of first-season ice types can be difficult because of ambiguous radar returns. Ambiguous returns seen on X-band radar imagery are attributed to snow cover. The data have indicated that changes in snow properties due to melting and refreezing cause development of a highly reflective medium to the 3 cm X-band radar. The 25 cm L-band radar is not noticeably affected by the observed phenomena, thus correlation of coincident X- and L-band imagery often resolves interpretation ambiguities on the X-band imagery caused by the snow effects. The data suggest that L-band radar energy often penetrates the ice and that subsurface returns are received. These returns also produce ambiguities in interpretation. Apparent smooth surfaces do not show this effect, but rough surfaces which have widely different roughness densities may produce apparently equal backscatter of L-band radar. Ice ridge identification and discrimination was often poor due to the obscuring effects of background clutter associated with the above-suggested backscattering phenomena. Small ridge sizes versus system resolution and steep angles of incidence also reduce ridge identification capabilities. Some icebergs produced time-delayed L-band signals, indicating internal reflections within the iceberg. Iceberg/water interface reflections rather than volume scattering are indicated. L-band radar cannot be depended upon for iceberg identification, since icebergs may be only partially imaged or not imaged at all by this frequency.