Humidity Correction

Air moisture can affect flux measurements (Schotanus et al., 1983). An air temperature and humidity sensor (e.g., CS500, Campbell Sci., Inc., Logan, Utah) needs to be mounted next to an eddy covariance system in order to obtain the vapor pressure in the air, which can be used to make moisture corrections to H (Schotanus et al., 1983). In addition to this correction, when the turbulent flux of any constituent is measured by the eddy covariance system, the simultaneous flux of any other entity needs to be taken into account. In particular, heat or water vapor can cause expansion of the air and thus affect the constituent's density and flux. Corrections can be done for LE flux based on the vapor and heat flux's effects on the densities of moist air (Webb et al., 1980). In flux measurements for a full-canopy pecan orchard in Las Cruces, New Mexico, USA (Wang et al., 2007), humidity-corrected ET was only 3% different from uncorrected values; the corrected sensible heat flux was 30% different from the uncorrected (sensible heat flux was near zero at this orchard). Usually the error related to the uncorrected fluxes can be 0-50%

(http://www.licor.com/env/Products/GasAnalyzers/eddyPresentation/EC_master_Presentation _files/_frame.htm).

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