Microwave brightness temperatures of the greenland ice sheet

Abstract

Microwave brightness temperatures measured by the Scanning Multichannel Microwave Radiometer on NIMBUS-7 over the Greenland ice sheet are analyzed for temporal, spatial, and frequency and polarization variations. Two periods are investigated, November 1978 to October 1980 and January to March 1982, i.e. including two summer and three winter periods. In the central part of the ice cap there exists an area with very small variations in brightness temperature, seasonally and annually, especially at the lower frequencies and at vertical polarization. During winter periods the standard deviation of brightness temperatures is of the same order of magnitude as that of the radiometric resolution of the instruments. It is found that the difference between brightness temperatures at the two polarizations vary with frequency and with the place of observation with a large difference in the north (55 K to 60 K) to a smaller one in the south (40 K to 50 K). Also, the slope of polarization difference versus frequency decreases with the position from north to south. The brightness temperature versus frequency relationship is a complex function of the position on the ice sheet. There appears to be an inversion from north to south with respect to “slope” with a positive slope in the north and a negative in the south with a neutral area in central Greenland.