Significance of non-isotropic scattering from vegetation for geobotanical remote sensing

Although it has been known for quite some time that individual leaves display non-Lambertian scattering at wavelengths of strong absorption in the visible part of the spectrum, while displaying near-Lambertian behaviour at wavelengths of little absorption in the near-infrared, this is widely ignored in geobotanical remote sensing investigations. Preliminary data show that non-Lambertian behaviour may have a significant effect on the ratio of infrared/red reflectance with changing illumination and observation angles, but little or no efTect on the location of the steep rise in reflectance from the red to the infrared ('red edge'). These results indicate the need for a complete assessment of directional scattering from different vegetation and canopy types, and strongly suggest the need for caution in interpretation of observational data taken without regard for illumination and observation angles.