Temperature/Humidity Intrared Radiometer (THIR)

Description

The Nimbus 7 Temperature-Humidity Infrared Radiometer (THIR) detected emitted thermal radiation in both the 10.5- to 12.5-micrometer region (IR window) and the 6.5- to 7.0-micrometer region (water vapor). The window channel provided an image of the cloud cover and temperatures of the cloud tops, land, and ocean surfaces. The other channel provided information on the moisture and cirrus cloud content of the upper troposphere and stratosphere, and the location of jet streams and frontal systems. The ground resolution at nadir was 6.7 km for the window channel and 20 km for the water vapor channel. Data from these two channels were used primarily to support other sophisticated meteorological experiments onboard Nimbus 7. The instrument was a non-imaging radiometer consisting of a 12.7 cm Cassegrain system and scanning mirror common to both channels, a beam splitter, filters, and two germanium-immersed thermistor bolometers. Incoming radiant energy was collected by a flat scanning mirror inclined at 45 deg to the optical axis. The mirror rotated through 360 deg at 48 rpm and scanned in a plane normal to the spacecraft velocity. The energy then was focused on a dichroic beam splitter which divided the energy spectrally and spatially. The two channels of this sensor transformed the received radiation into electric outputs (voltages), which were digitized and recorded on magnetic tape for subsequent playback to a ground acquisition station. For more complete information on instrument and data products, see Section 9 in "The Nimbus 7 Users' Guide" (TRF B30045) and the "Nimbus 7 Temperature-Humidity Infrared Radiometer (THIR) Data User's Guide" (TRF B30601), both available from NSSDC. Except for data being digitized on board, the Nimbus 7 THIR was of the same design and operation as the THIR flown on Nimbus 4, 5, and 6. The instrument was turned off in 1985 to conserve power.