A Proposed Improved Method of Radiosonde Humidity Sensing
Environmental research papers,
PHILLIPS LAB HANSCOM AFB MA
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The carbon humidity element has been used in most U.S. radiosonde flights for the past twenty-five to thirty years. Although it is arguably the best radiosonde humidity sensor in use, the carbon element has physical characteristics that result in significant measurement errors as employed in todays synoptic radiosonde flights. The principal characteristics causing errors are its requirement to be in temperature equilibrium, its poor time response at low temperatures, and its poor sensitivity at low relative humidities. A proposal is made to employ the carbon element in a servo loop designed to control the temperature of the element in such a way as to maintain the measured relative humidity at 33 percent. The temperature of the element will then be used to determine either dew point or the partial pressure due to water vapor. This method will eliminate or significantly reduce the errors arising from the main error source and from some others as well.