The Nimbus-3 Medium-Resolution Infrared Radiometer (MRIR) Level 1 Meteorological Radiance Data contain radiances expressed as equivalent blackbody temperatures along with geolocation, time and other housekeeping information. These Nimbus-3 MRIR data are stored in a 36-bit IBM binary or TAP format (proprietary tape emulated format).

The Nimbus-3 satellite was launched on 14 April 1969, and is the follow-on experiment to the MRIR flown on Nimbus-2. MRIR was designed to measure electromagnetic radiation emitted and reflected from the earth and its atmosphere at 5 wavelengths. The five wavelengths regions are as follows:
                  
* 6.5 to 7.0 microns - This channel covers the 6.7 micron water vapor absorption band. Its purpose is to provide information on water vapor distribution in the upper troposphere and, in conjunction with the other channels to provide data concerning relative humidities at these altitudes.
                  
* 10 to 11 microns - Operating in an atmospheric "window," this channel measures surface or near-surface temperatures over clear portions of the atmosphere.  It also provides cloud cover and cloud height information (day and night).
                  
* 14.5 to 15.5 microns - This channel, centered about the strong absorption band of C02 at 15 microns, measures radiation which emanates primarily from the stratosphere. The information gained here is of primary importance to in following seasonal stratospheric temperature changes.
                  
* 20 to 23 microns - This channel yields data from the spectral region containing the broad rotational absorption bands of water vapor. It will provide information similar to that of the 6.5 to 7.0 micron channel except that the flux will largely be radiated from lower in the atmosphere.
                  
* 0.2 to 4.0 microns - This channel covers more than 99% of the solar spectrum and yields information on the intensity of the reflected solar energy from the earth and its atmosphere.
                  
The MRIR instrument was operational from May 15, 1966 through July 28, 1966. On September 25, 1970, the satellite's rear horizon scanner failed, making it impossible to determine where the MRIR sensor was pointing. The experiment was operated periodically until January 22, 1972, when all spacecraft operations were terminated.

These data were previously archived at NASA NSSDC as product NMRT-MRIR under the entry ID ESAD-00183 (originally 69-037A-05B).