ISHS Acta Horticulturae 449: II International Symposium on Irrigation of Horticultural Crops
SURFACE RENEWAL ESTIMATES OF EVAPOTRANSPIRATION. TALL CANOPIES |
| Authors: | D. Spano, P. Duce, R.L. Snyder, K.T. Paw U |
| Keywords: | Sensible heat flux, energy balance, eddy covariance, coherent structures, structure functions |
| Abstract:
Sensible heat flux density (HSR) was determined over grapevine and avocado tree canopies using the surface renewal (SR) method that was first proposed by Paw U and Brunet (1991). The method employs high frequency temperature measurements above canopies to calculate H values using a conservation of energy equation. The HSR estimates increased with measurement height above the canopies, and a calibration factor (a) was needed to improve H estimates. This a is believed to result from unequal heating of the mean air volume under the measurement height. The grapevines have a sparse canopy, whereas the avocado orchard has a dense canopy. This may explain the difference in observed a values. However, more research is needed to better understand a. Evapotranspiration (lESR) was calculated using net radiation and soil heat flux density and HSR in the energy balance equation. An independent measure of H, obtained from a sonic anemometer, was used to calculate evapotranspiration (lE) for comparison with IESR values. High correlations were observed between IESR and lE for both crops. When the a values were used to determine HSR and a regression of lESR versus lE was computed, the coefficient of determination values were R2 = 0.96 for avocado trees and R2 = 0.93 for grapevines. | |
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