Time evolution of the microwave signatures of a drifting Arctic ice feature in 1996-1997

A large second-year ice feature, observed in autumn 1996, has been tracked during its drift, from October to the end of May. Its active microwave characteristics, obtained from scatterometers in C- and Ku-band, have been compared to the brightness temperatures, the gradient ratio and the multiyear ice concentration derived from the SSM/I data. Ice, highly reflective at C-band, located in the center of the feature, appears as a cluster on the scatter plot in (19, 37-vertical polarization) brightness temperature space. Situated under the main line characterizing consolidated ice on the feature, these points are associated to a relatively high gradient ratio. The NASA team algorithm interprets these observations as low multiyear ice concentrations. Despite their inability to give a direct estimation of the multiyear ice concentration, scatterometers present, through the cold season, coherent sets of data which can help to identify areas of homogeneous type within old ice. For this purpose, scatterometers in C-band (5.3 GHz) provide observations which complete those of the SSM/I while data in Ku-band (14.5 GHz) appear to be close to the 19 GHz brightness temperatures.