In a recent series of flights over the marginal ice zone in the Greenland Sea the Naval Research Laboratory demonstrated that millimeter wavelength radiometry can be used for the remote determination of sea ice edge properties under all weather conditions. The imaging measurements, obtained at 90 GHz (3.3 mm) and 140 GHz (2.1 mm) from high altitude through heavy cloud conditions, can be used to delineate the sea ice edge, to locate polynyas and leads, to measure ice concentration, to determine ice type, age, and thickness, and to quantify the sea surface wind and atmospheric properties. Sea ice images were also obtained at 220 GHz (1.4 mm) but only under clear atmospheric conditions. The location, movement, and concentration of the sea ice edge greatly affects the dynamics of ice-ocean circulation and air-sea interaction. This information is fundamental for accurate long-term weather prediction and for ship operations. These are the first measurements of sea ice ever obtained at 140 and 220 GHz.