Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 26, 2003
Publication Date: July 15, 2005
Citation: Baker, J.M. 2005. Humidity. In: Hatfield, J.L, Baker, J.M. editors. Micrometeorology in Agricultural Systems. Agronomy Monograph No. 47. Madison, WI: ASA-CSA-SSSA. p. 31-42. Technical Abstract: Humidity is one of the fundamental variables that characterize the state of the atmosphere, so its measurement is necessary for a wide array of purposes. It can be measured in a variety of ways, each with strengths and weaknesses. Wet/dry bulb psychrometers permit estimation of humidity from temperature measurements alone, but they require frequent attention. Dewpoint hygrometers provide accurate, direct measurement of humidity, but they are relatively expensive and susceptible to contamination. Infrared hygrometry is the method of choice for high frequency measurement of vapor density, as is needed in eddy covariance measurement of evaporation rate, but they are too expensive for routine monitoring applications, where relative humidity sensors are probably the best choice. These have improved markedly in recent years, and now can provide long-term operation at low cost with accuaracy sufficient for many purposes.