During the Marginal Ice Zone Experiment in the Fram Strait in June--July 1984, a number of aircraft with microwave sensors and the scanning multichannel microwave radiometer (SMMR) on board the Nimbus 7 satellite were used to acquire large--scale and mesoscale ice--ocean observations in conjunction with local surface measurements made by experimenters based on helicopter--equipped ice--strengthened vessels. An analysis of the data acquired during six flights of one such aircraft, the NASA CV--990 airborne laboratory, is discussed in this paper. Included in the instrument complement of the CV--990 were two passive microwave imagers operating at wavelengths of 0.33 and 1.55 cm and the airborne multichannel microwave radiometer (AMMR) operating at wavelengths of 0.81, 1.4, and 1.7 cm for both horizontal and vertical polarizations. Total and multiyear sea ice concentrations calculated from the AMMR data were found to agree with similar calculations using SMMR data. This is the first check of the performance of the SMMR Team ice algorithm for near-melting point conditions. The temperature dependence of the multiyear sea ice concentration determination near the melting point was found to be the same for both airborne and spacecraft instrument data and to be correlated with presence or absence of clouds. Finally, it was found that a spectral gradient radio using the data from both the 0.33- and 155-cm radiometers provides more reliable distinctions between low total ice concentrations and open water storm effects near the ice edge than does either singly. ¿ American Geophysical Union 1988