Abstract :
Although it is difficult to describe the nature of clear air turbulence (or CAT), we know its effect¿the sudden vibration experienced by an aircraft in flight in a stormfree, cloudfree sky. It is evident that this turbulence is an eddy motion of the air that disrupts its uniform flow, a motion such as that associated with jet streams; however, we do not know exactly how it is generated. Because the effects of CAT can range from mere passenger discomfort to actual loss of an aircraft, it is important to devise some method of warning the pilot of turbulent areas to be avoided. Various indirect and direct detection systems, employing both active and passive techniques, are currently being investigated, but thus far all have exhibited serious limitations on effective performance. One reason for this is the lack of data concerning the phenomenon they are designed to detect.
