Lidar/Laser Spectrometers
type: Concept

JPL LASER HYGROMETERS
type: Concept
change note: 2021-08-04 17:21:29.0 [sritz] insert AltLabel (id: null category: primary text: JPL LASER HYGROMETERS language code: en);
definition: Laser hygrometers measure the amount of water vapor directly via absorption of laser light. If the initial strength of the laser and the path length through which it travels is known, measuring the diminution of its intensity will give an indication of the amount of water vapor present. The JPL Laser Hygrometer uses this principle in an open-path instrument; that is, the laser path is in the free stream passing by the aircraft. A tunable diode laser operating at 1.37mm is mounted in a window blank (an aluminum panel which replaces the passenger window) on the port side of the NASA DC-8. The laser and detector are mounted on a circular aluminum disk in the upper rectangular 'arm' of the instrument. Exactly 25cm away is a 0.5 inch diameter mirror from which the laser beam is reflected. This gives a path length of 50cm- from the laser, down to the mirror and back to the detector. The length of the arms insures that the instrument is well outside the boundary layer of the aircraft minimizing effects of the aircraft itself upon the measurements. Additional information available at "http://ghrc.msfc.nasa.gov/uso/readme/c4djlh.html" [Summary provided by Global Hydrology Resource Center]
in scheme: instruments