NOAA KLM User's Guide
The first High Resolution Infrared Radiation Sounder (HIRS) instrument was developed and flown in 1975 on the Nimbus 6 satellite. Results from the Nimbus 6 orbital data and system studies showed promise of obtaining data from which improved atmospheric soundings could be derived. The basic design for the Nimbus HIRS system was modified to accommodate the TIROS-N series of spacecraft with TIROS-N orbital requirements, to improve the sensor performance, and to increase the reliability of the filter wheel drive assembly. This HIRS/2 design was used in the protoflight and seven flight models and further improved to become HIRS/2I. Three HIRS/2I units were built. Additional improvements and operational changes were made for the HIRS/3. Three HIRS/3 were built for use on the NOAA KLM spacecraft.
The HIRS/4 design is a modification of the HIRS/3 design, built to fly on the NOAA-N, -P spacecraft. The design changes for the HIRS/4 consist of: 1) radiant cooler operation at 95 K; 2) IFOV size reduced to 10 km; 3) inclusion of a fifth Internal Warm Target (IWT) temperature sensor; and 4) addition of a tertiary telescope temperature sensor. Section 3.2.1 specifically discusses the HIRS/3 instrument (flown on NOAA KLM), while Section 3.2.2 contains descriptions of the HIRS/4 instrument (flown on NOAA-N and -P).
Amended April 5, 2004
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