CHARACTERIZING THE TOPOGRAPHIC EFFECT AT RED WAVELENGTHS USING JUVENILE CONIFER CANOPIES

The topographic effect has been characterised precisely from measureme nts of nadir-viewed radiance at red wavelengths, for a non-Lambertian canopy constructed from juvenile conifers. The conifers were mounted o n a topographically-orientable platform, the aspect and slope of which are independently variable, allowing incidence and exitance effects t o be examined separately. Measurements show both that the variation in radiance with topography is dominated by incidence rather than exitan ce effects, and that incidence and exitance effects appear to be large ly independent. The variation in radiance with orientation of the juve nile conifer canopy is well-represented by a simple analytical functio n of the cosines of the incidence and exitance angles, provided that t he canopy radiance arising from diffuse sky irradiance is explicitly c onsidered.