Comparison of Nimbus 7 scanning multichannel microwave radiometer radiance and derived sea ice concentrations with Landsat imagery for the north water area of Baffin Bay

Landsat imagery for the northern Baffin Bay (May to June, 1981) is used to compare ice concentration estimates derived from Nimbus 7 scanning multichannel microwave radiometer (SMMR) data. Periods of premelt, onset of melt and melt are identified based on changes in brightness temperature and on gridded air temperature data from the European Center for Mid‐Range Weather Forecasting. Differences between multispectral SMMR‐ and Landsat‐derived total ice concentrations are within 3.5% for premelt and onset of melt periods. During melt, differences increase to about 10%. Differences for individual SMMR footprints are greater and contribute to a mean correlation coefficient of 0.53 between SMMR‐ and Landsat‐derived ice concentrations. The SMMR data yield slightly lower estimates of total ice concentration, and for individual SMMR footprints they tend to yield lower estimates at high concentrations and higher estimates at low concentrations relative to the Landsat interpretation. Although statistically different, the mean concentrations derived using the Landsat and SMMR data were separated by less than 10% in virtually all cases. Possible reasons for these discrepancies are discussed. The brightness temperatures for compact pack ice compared with fast ice are on the average 10 K higher at vertical polarization and 15 K higher at horizontal polarization for 18 and 37 GHz during the premelt period. Classification of ice types such as first‐year ice, young ice, and nilas by means of polarization ratios seems feasible for large homogeneous areas of a single ice type.