MICROWAVE RESPONSE TO STRESS IN SEA-ICE - A REPORT ON INITIAL FIELD-TESTS

An initial field test was conducted to determine if the stress state o f sea ice has an effect on its microwave signature. The tests were con ducted during March and April of 1992 in the Beaufort Sea. An inflatab le jack was placed into a vertical slot in the ice to induce stress in the ice while a microwave transmitter/receiver monitored the backscat ter from the ice. Measurements were made at X-Band and C-Band frequenc ies, with various polarization combinations, on 1.3 m thick first-year ice and on a freshwater melt pond within a multiyear flee. Changes in backscatter were seen in both the first-year ice and the melt pond ic e at both X-Band and C-Band frequencies, but not at all polarizations and orientations. In general, the largest change in microwave response took place when the ice was pressurized for the first time. The measu red changes in microwave response were less than 2 dB. However, after accounting for the mismatch between the radar footprint and the size o f the area stressed, the effect on the backscatter signal was 13 dB. R esponse was seen at jack pressures at low as about 70 kPa, which resul ted in an average stress over the radar footprint of about 13 kPa. In comparison, natural pack ice stresses range up to 400 kPa.