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Closed-path Laser Hygrometer (CLH)


Operational (Last flown in 2006; unchanged and still operational)
Operated By: 
Replaced By: 

Anna Luebke, Linnea Avallone, and Jess Landeros working on the CLH instrument.

The University of Colorado closed-path tunable diode laser hygrometer (CLH) is based on the water vapor hygrometers designed by R. D. May (Maycomm, Inc.). CLH is coupled to a heated, forward-facing inlet that enhances particulate water by anisokinetic sampling. Ice water content (IWC) is derived from the measurement of enhanced total water, with knowledge of the instrument sampling characteristics, particle size distributions and ambient water vapor.

In contrast to the open-path systems of similar heritage, the CLH, which was designed for operation in the troposphere on commercial aircraft, has a single-pass absorption cell (27.62 cm long). The light source is a room-temperature solid-state laser that puts out 3-5 mW of radiation at 1.37 mm (7306.752 cm-1).

Instrument Type: 
Gulfstream V - NSF, WB-57 - JSC, DC-8- AFRC
Recent Missions: 
SOLVE (DC-8- AFRC); PUMA (WB-57 - JSC); MACPEX (WB-57 - JSC); TC4 (WB-57 - JSC); MidCiX (WB-57 - JSC); CRYSTAL FACE (WB-57 - JSC)
Complete mission list:
Point(s) of Contact: