The Infrared Thermometer (IRT) is a ground-based radiation pyrometer that provides measurements of the equivalent blackbody brightness temperature of the scene in its field of view. The downwelling version has a narrow field of view for measuring sky temperature and for detecting clouds. The upwelling version has a wide field of view for measuring the narrowband radiating temperature of the ground surface.
The IRT data with the SKYRAD comes from the IRT instrument, but from a different port. The IRT data are serial-sampled and the SKYRAD irt values are analog sampled. If there is a problem with the infrared temperatures from one instrument and not the other, then there is likely a port/wiring issue. If the actual instrument fails, the data for both the IRT and SKYRAD datastreams should be bad.
In August 2005, an upgraded version of the IRT was installed at the SGP extended facilities (but not SGP C1). This newer model has a lower temperature range (see table below) and is located inside a positively pressurized box, with an opening for the IRT view (see image right). This will help keep dirt and other objects from collecting on the mirror between times of the bi-weekly site visits.
For more information see IRT.