Scale effects and scaling-up by geometric-optical model

Many physical laws, principles, measurements, etc., are applicable only to either a point or a homogeneous surface. However, remote sensing is dealing with pixels which ranging from meters to kilometers. Therefore scale effects of these laws and measurements are inevitable science problems to be faced. It is convenient but dangerous to assume those great physics laws and principles are automatically applicable to heterogeneous land surface at the scale of pixel size. As examples, the authors briefly explain the scale effects of BRDF, albedo measurements, and of Beer´s law and the principle, of reciprocity. The authors concentrate on the spatial scale effect of Planck law and its scaling-up by a geometric-optical model. When the land surface at the scale of AVHRR or MODIS can not be regarded as isothermal, they have to scale the law up for thermal infrared remote sensing of the land surface