The Nimbus-4 Infrared Interferometer Spectrometer (IRIS) Level 1 Radiance Data contain thermal emissions of the Earth's atmosphere at wave numbers between 400 and 1600 cm-1, with a nominal resolution of 2.8 cm-1. The data also contain documentation information, reference calibration, average instrument temperatures, and a summary for each orbital pass. The data, originally written on IBM 360 machines, were recovered from 9-track magnetic tapes. The data are archived in their original IBM 32-bit word binary record format, and each file contains an entire day of measurements. The product contains data from April 9, 1970 (day of year 99) through Jan 31, 1971 (day of year 31). The IRIS instrument was designed to provide information on the vertical structure of the atmosphere and on the emissive properties of the earth's surface by measuring the surface and atmospheric radiation in the 6.25 to 25 micrometer range using a modified Michelson interferometer. IRIS viewed along the satellite track direction with a spatial resolution of 94 km at nadir. A Fourier transform was applied to the interferograms to produce thermal emmision spectra of the Earth which could be used to derive vertical profiles of temperature, water vapor, and ozone, as well as other parameters of meteorological interest. The Infrared Interferometer Spectrometer (IRIS) experiment on Nimbus-4 is a follow on experiment to the Nimbus-3 IRIS experiment. The IRIS Principal Investigator was Dr. Rudolf A. Hanel. These data were previously archived at NASA NSSDC under the entry ID ESAD-00093 (originally 70-025A-03A).