Summary

Description

The Nimbus High Resolution Infrared Radiometer (HRIR) was originally 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 Nimbus III HRIR was modified 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. The Nimbus III HRIR data are stored in a binary TAP format (proprietary Tape emulated format). The HRIR instrument was launched on the Nimbus-3 satellite and was operational from April 14, 1966 through July 22, 1969. [Summary Extracted from the Nimbus III users' guide]