TERMIUM Plus^®

Record 1,  Textual support,  English

Record number: 1, Textual support number: 1 CONT

The laser (or lidar) velocimeter [lidar = light radar] operates in a fashion entirely analogous to that of the airborne Doppler weather radars likely soon to be available for detecting turbulence in storm cells. As with radars, the device detects air movements by observing the motion of particles suspended in the air and carried with it. The only significant difference is that a beam of coherent infrared radiation is used to scan ahead of the aircraft, instead of a beam (or series of pulses) of radio energy in the considerably longer-wavelength microwave band. The frequency of the back-scattered echoes or reflections undergoes Doppler shift detection by standard heterodyning techniques, which involve comparing the frequency of the reflected illumination with that of the original laser beam. Any reflecting object or material which has motion relative to the transmitter/receiver will cause a detectable shift in frequency, which can be isolated from the transmitter's own proper motion (over the ground) and thus yield a precise indication of the speed at which the air is moving several hundred metres in front of the aircraft. From this data, it is easy to compute what the air speed of the aircraft will be when it reaches that particular patch of air in a few seconds' time [and hence detect possible turbulence ahead].  2, record 1, English, - laser%20velocimeter

Record 1,  Textual support,  French

Record number: 1, Textual support number: 1 CONT

Le principe de fonctionnement du vélocimètre à laser (ou lidar) est exactement le même que celui des radars météorologiques Doppler de bord, qui doivent être mis en service prochainement pour la détection des turbulences dans les systèmes d'orages.  1, record 1, French, - v%C3%A9locim%C3%A8tre%20%C3%A0%20laser

Record 1,  Textual support,  Spanish