Humidity Fluctuations over a Vegetated Surface Measured with a Lyman-Alpha Hygrometer and a Fine-Wire Thermocouple Psychrometer

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  • 1 Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Nebraska 68583
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Abstract

Simultaneous measurements of humidity fluctuations over a crop made with a specially modified Lyman-alpha hygrometer and a fine-wire thermocouple psychrometer are compared. Standard deviations of the two sets of data are comparable except occasionally when wind speeds were low. The psychrometer appears to underestimate the vertical flux of water vapor due to its slow response. Analysis of humidity spectra and moisture flux cospectra shows that the Lyman-alpha hygrometer is superior to the psychrometer in response at high frequencies and low wind speeds.

Abstract

Simultaneous measurements of humidity fluctuations over a crop made with a specially modified Lyman-alpha hygrometer and a fine-wire thermocouple psychrometer are compared. Standard deviations of the two sets of data are comparable except occasionally when wind speeds were low. The psychrometer appears to underestimate the vertical flux of water vapor due to its slow response. Analysis of humidity spectra and moisture flux cospectra shows that the Lyman-alpha hygrometer is superior to the psychrometer in response at high frequencies and low wind speeds.

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