Clear air turbulence (CAT) is frequently associated with horizontal temperature gradients of the atmosphere. An instrument has been developed for detecting such gradients remotely by sensing the infrared radiation emitted by the carbon dioxide in the atmosphere. Three of these instruments have been installed on commercial jet aircraft, to evalute this technique for providing advance warning of CAT. Many light turbulence encounters have been detected as much as 80 miles (130 km) (8 min) in advance. A high false alarm rate was experienced because of temperature gradients not associated with turbulence. No severe turbulence has been encountered to date. It is hoped that the temperature effects associated with severe turbulence will be large enough to permit establishing higher alarm threshold levels which will substantially reduce the false alarm rate. Future plans include evaluation of a vertical scan mode for detection of temperature inversions.
R. W. Astheimer, "The Remote Detection of Clear Air Turbulence by Infrared Radiation," Appl. Opt. 9, 1789-1797 (1970)