Field observations of microwave backscatter from Weddell Sea ice

Abstract

During September and October, 1989, we made backscatter measurements over sea ice in the Weddell Sea using a ship-based 13·5-GHz radar at incidence angles from 0° to 30° with VV polarization. The objectives of these measurements were to document microwave signatures of Antarctic ice morphologies and to determine the geophysical processes responsible for microwave scattering. The frequency of 13·5 GHz is similar to that used on operational satellite radar altimeters. We found that two characteristics of the snow cover dominated the measured backscatter coefficients (σ⁰). A thick snow cover increased σ⁰ at oblique incidence due to volume scatter. Slush at the snow/ice interface increased σ⁰ by about 8 dB at normal incidence because the smooth surface of the slush layer represents a stronger dielectric boundary. Our results indicate that it may be possible to monitor the formation and subsequent freeze-up of this slush layer using satellite radars. Field observations have shown that this slush can be a significant source of new ice formation, contributing as much as 16 per cent to the total sea ice volume found in the Weddell Sea.