MEASUREMENT OF ATMOSPHERIC DEWPOINT FROM AIRCRAFT.
NAVAL RESEARCH LAB WASHINGTON D C
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By cooperative efforts of government and industry, the absolute measurement of atmospheric humidity has now become practical under operational aircraft flight conditions by use of thermoelectrically cooled dewpoint hygrometers with optical detection of condensate and automatic mirror temperature control. Effects of salt contamination can be minimized by in-flight check and adjustment of the dew thickness control level with the contamination present on the mirror. Interfacing of the sensor and aircraft is not amenable to a universal solution for all aircraft but a mounting arrangement has been developed to permit in-flight adjustment of flow and pressure at the sensor. On Navy Constellation aircraft, a radome can be used as a rain deflector to reduce the entry of liquid water while flying in hurricanes or other precipitation. Mechanical aspiration of the sensor can remove accumulated water in rain and permit measurement of dewpoint on the ground. However, because the dynamic heating evaporates water at any aircraft surface or instrument, data in clouds or precipitation in general must indicate humidity greater than saturation with any type of hygrometer. Total evaporation of cloud water can provide useful information on the total water content of the clouds with a dewpoint instrument designed for this purpose. Author