Directional Effect on Change of Spatial Scale Over Heterogeneous Surface in Thermal Infrared Remote Sensing

摘要

The issue of deriving cross-scale aggregation rules has been heavily investigated during the past two decades. The widely used approach consists of formulating grid-scale surface fluxes using the same equations that govern the patch-scale behavior but whose arguments are the aggregate expressions of those at the patch-scale (Becker, Chehbouni). Such approach has been used in the past derive area-averaged or effective radiative surface temperature as it might be observed using low spatial resolution satellite data. The problem however is such satellite data exhibits large directional effect and none the past studies have addressed this issue. The present work tackles this issue of the combined effects of surface heterogeneity and view angle variations on surface temperature measurements. The directional effects are modeled on surfaces having a known heterogeneity. Then, the angular properties of local surfaces, assumed homogeneous, are calculated according a multiple scattering model. By applying the principle of aggregation, the equivalent angular radiance of the whole heterogeneous scene is then defined. This made it possible to show that this radiance is particularly sensitive to the directional effects, in particular when the spatial variation of surface temperature is significant and when there is a vegetation component in the heterogeneous land surface. The structure of the vegetation component is also a significant factor of directional effect on equivalent angular radiance.