Examination of the factors controlling directional effects on radiative surface temperature over vegetated surfaces

In this study, the effect of view angle variation on surface radiative temperature measurements has been examined from both experimental and modeling perspectives. A coupled SVAT-vegetation functioning model associated with a radiative transfer model in thermal infrared has been used to document the factors controlling the departure of nadir from off-nadir radiative surface temperature under different soil moisture conditions and vegetation status and dynamics. In the same vein, an experimental setup has been conceived to document the same effect over sparsely vegetated surfaces. This include 3 infrared radiometers observing the same spot at 0, 45 and 55 degrees, respectively. The experimental results indicated differences between nadir and off-nadir radiative temperature of up to 5 K. The data also illustrated that, under clear sky and constant vegetation conditions, this difference is well correlated with surface soil moisture. However, the correlation decreased when the same comparison was made under changing vegetation conditions.