Definition and invariance properties of structured surface BRDF

The bidirectional reflectance distribution function (BRDF) is used to characterize the directional properties of surface reflectance, but the most recent standardized definition fails to address some important aspects for the structured and varying surfaces encountered in remote sensing. This paper proposes an updated definition of BRDF that is applicable for such surfaces. The updated definition then motivates an examination of the resulting measurement requirements and invariance properties. The conclusion is that structured surface BRDF can be defined in a consistent manner that is an intrinsic surface property, and it does exhibit the usual invariance properties associated with BRDF, such as reciprocity.