BRDF calibration of natural samples in support of remote sensing

In this study laboratory BRDF measurements of leaf samples are presented in an effort to understand the role of spatial and spectral variability of the natural biome. The samples measured in the laboratory included fresh and dry leaves from a poplar tree (Liriodendron tulipifera) and an acacia tree (Acacia greggii). Three different size samples were created: whole leaves, samples between 4 and 4.75 mm, and samples between 1.7 and 2 mm. The BRDF was measured at incident angles of 0deg and 67deg and at wavelengths of 340 nm, 470 nm and 870 nm. It is shown how the BRDF depends on the incident and scatter angles. The shapes of the BRDF curves strongly depend on the nature of the sample (i.e. crushed versus whole leaf). These laboratory results were compared with airborne measurements of BRDF from NASA's Cloud Absorption Radiometer (CAR) instrument.