Estimation of surface sensible heat flux using dual angle observations of radiative surface temperature

In this study, dual angle observations of radiative surface temperature hav e been used in conjunction with a two-layer model to derive sensible heat f lux over a sparsely vegetated surface. Data collected during the semi-arid- land-surface-atmosphere program (SALSA) over a semi-arid grassland in Mexic o were used to assess the performance of the approach. The results showed t hat this approach led to reasonable estimates of the observed fluxes. The m ean average percentage difference (MAPD) between observed and simulated flu xes was about 23%, which is not statistically different from the expected 2 0% scatter, when different flux measuring devices are compared over the sam e site. However, the sensitivity analysis indicated that the approach was r ather sensitive to uncertainties in both measured radiative temperatures an d aerodynamic characteristics of the vegetation. Finally, the issue of usin g dual angle observations of surface temperature for characterizing the dif ference between aerodynamic and nadir viewing radiative temperature has bee n examined. The results showed that this difference is linearly correlated with the difference between nadir and oblique radiative temperatures. Based on this finding, we expressed sensible heat flux in terms of the (nadir) r adiative-air temperature gradient and a corrective term involving the nadir -oblique temperature differences. This formulation has been successfully te sted. The resulting MAPD was about 33%. (C) 2001 Elsevier Science B.V. All rights reserved.