In 1969, the IRIS (Infrared Interferometer Spectrometer) aboard the Nimbus-3 polar-orbiting satellite measured earth-atmosphere-emitted radiances at high spectral resolution for the first time. Over the desert, surface temperatures of 320 K were observed in the 11-µm window region of the spectrum and tropopause emissions of 210 K were observed in the 15-µm absorption band. Closer toward the center of the carbon dioxide absorption band, the radiation temperature decreases due to the decrease of temperature with altitude in the troposphere. The IRIS had 100-km resolution and was nadir-viewing only. These interferometer measurements of the terrestrial spectrum revealed details of the carbon dioxide, water vapor, and ozone absorption bands never seen before (Hanel et al. 1970).