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Lyman Alpha-Hygrometer


Operated By: 


Instrument: Lyman Alpha-Hygrometer

Principal Investigator: Ken Kelly

NOAA/ERL/Aeronomy Laboratory
325 Broadway MS R/E/AL6
Boulder, CO 80303

Principle of Operation: A 121.6 nm light source dissociates a fraction of the water and forms excited hydroxyl radicals. These radicals will either fluoresce at 309 nm or be quenched by air molecules. A PMT measures the 309 nm light, which is proportional to the water vapor mixing ratio. A photodiode monitors the 121.6 nm intensity at the same distance as the sample chamber center. An in-flight calibration is obtained from the measured absorption of 121.6 nm light by injected water vapor, the known absorption cross section and the chamber pressure. The hygrometer will measure total water.

Accuracy: 6%
Detection Limit: 0.1 ppmv
Response Time: 1 Second
Location on ER-2: Q-Bay

Reference: Kley, D., A. Schmeltekopf, K. Kelly, R. Winkler, T. Thompson, M. McFarland. "The U-2 Lyman-Alpha results from the 1980 Panama Experiment." The 1980 Stratospheric-Tropospheric Exchange Experiment. Ed: A.P.Margozzi. NASA Technical Memo 84297 (1983): 85-125.



Point(s) of Contact: 
Ken Kelly (POC; PI)