Ha. Cleugh et Fx. Dunin, MODELING SENSIBLE HEAT FLUXES FROM A WHEAT CANOPY - AN EVALUATION OF THE RESISTANCE ENERGY-BALANCE MODEL, Journal of hydrology, 164(1-4), 1995, pp. 127-152
Sensible heat fluxes measured over a growing wheat crop are used to ev
aluate the performance of the resistance energy balance model for both
sparse and full canopy covers. Aerodynamic temperatures (for heat and
momentum) are derived from measured sensible heat fluxes and then com
pared to canopy radiometric temperatures which were measured using inf
ra-red radiometers and a pyrgeometer. Agreement between measured radio
metric and aerodynamic temperatures is excellent for the more dense, f
ully-closed wheat crop, and the resistance energy balance model also p
erformed adequately for this canopy. However, very large differences b
etween radiometric and aerodynamic temperatures were observed for the
sparse wheat crop, especially at intermediate leaf area indexes (LAIs)
(less than 2). Large differences were even found between the infra-re
d radiometer-based and pyrgeometer-based canopy temperatures. Under su
ch conditions of sparse canopy cover the model performs poorly. At the
se times greater agreement between aerodynamic and canopy temperatures
was found when the latter was determined as a 'composite temperature'
, combining both infra-red radiometer and pyrgeometer measurements. Mo
delling of sensible heat flux using the resistance energy balance mode
l is improved with the use of this composite canopy temperature. Measu
red values for kB(-1) were extremely variable and so a unique value fo
r the ratio of roughness lengths for heat and momentum could not be de
termined.