The Nimbus III was launched on April 14 1969 and was a major upgrade from the Nimbus II satellite with an increase in the number of meteorological experiments from 4 to 7:
High Resolution Infrared Radiometer (HRIR)
Medium Resolution Infrared Radiometer (MRIR)
Infrared interferometer Spectrometer (IRIS)
Satellite Infrared Spectrometer (SIRS)
Monitor of Ultraviolet Solar Energy (MUSE)
Image Dissector Camera System (IDCS)
Interrogation, Recording and Location System (IRLS)
The Nimbus III High Resolution Infrared Radiometer (HRIR) was designed to perform two major functions: First, to map the Earth's cloud cover at night to complement the television coverage during the daytime portion of the orbit, and second, to measure the temperature of cloud tops and terrain features.
The single-channel dual-band pass scanning radiometer uses a PBSe photoconductive detector cell and provides measurements of blackbody temperatures 210K – 330K. The Scan mirror is inclined to 45 degrees with a scan rate of 44.7 revolutions per minute. The Instantaneous field of view is 8.8 milliradians and the scan line separation is 8.3 km. The ground resolution is 8 km at 1110 km.
The Nimbus III HRIR was designed to allow nighttime and daytime cloud cover mapping by use of dual band-pass filter which transmits 0.7 to 1.3 micron, and 3.4 to 4.2 micron radiation. The improvement of detector temperature control and electronics compensation has eliminated the multiple calibrations of previous instruments.
Nighttime operation was in the 3.4 to 4.2 micron near infrared region. Daytime operation was based on the predominance of reflected solar energy in the 0.7 to 1.3 micron region. Change-over from nighttime to daytime operation was accomplished automatically (or by ground station command), by actuating a relay in the early stages of the radiometer electronics. The system gain was reduced in the daytime mode to compensate for the higher energy level present.
More information can be found in the README file or Nimbus III users' guide.
You may download the Nimbus III HRIR data products by selecting the "Data Holding" link on the menu bar. If you have questions on GES DISC data product support and services for the Nimbus III HRIR and related data sets, please let us know.