The common way to check the accuracy of and calibrate covariance measurements is to check the energy balance. One can install net radiometers and soil heat flux plates to complete the energy balance measurements and use the energy balance method to check the result of LE calculations from the eddy covariance method (Sammis et al., 2005; Simmons et al., 2007).
The energy budget equation is:
If the energy is not balanced, there must be problems in one or more of the energy components. Problems in Rn measurements can occur when the sensor is not level or the domes have not been kept clean. Also, the net radiometer must be high enough to represent the average Rn over the canopy cover. Another problem is the measurement of G using soil heat flux plates. The number and distribution of the heat flux plates must be sufficient to give an average value for the canopy conditions. Because measuring the H component with the eddy covariance method involves a simpler technology than does measuring LE, it is assumed that the eddy covariance system measures H accurately except under certain conditions (low wind speed, stable stratification, in high canopies, or in any case when air mixing is significantly reduced or/and atmosphere-surface are decoupled. http://www.licor.com/env/Products/GasAnalyzers/eddyPresentation/EC_master_Presentation _files/_frame.htm). If all the components are measured accurately except LE, then one can calibrate the LE measurements of the eddy covariance equipment using the LE obtained from the energy budget equation (Sammis et al., 2005; Simmons et al., 2007). Researchers have used the Bowen ratio to correct both H and LE to get energy closure (e.g., Cleverly et al., 2002), but no rational reason is given to assume that both H and LE are in error using the eddy covariance technology. Before calibrating the LE measurements using energy closure, it is important to make all the proper corrections for the calculation of H and LE from the eddy covariance technology.
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