Characterising the topographic effect at red wavelengths using juvenile conifer canopies
The topographic effect has been characterised precisely from measurements of nadir-viewed radiance at red wavelengths, for a non-Lambertian canopy constructed from juvenile conifers. The conifers were mounted on a topographically-orientable platform, the aspect and slope of which are independently variable, allowing incidence and exitance effects to be examined separately. Measurements show both that the variation in radiance with topography is dominated by incidence rather than exitance effects, and that incidence and exitance effects appear to be largely independent. The variation in radiance with orientation of the juvenile conifer canopy is well-represented by a simple analytical function of the cosines of the incidence and exitance angles, provided that the canopy radiance arising from diffuse sky irradiance is explicitly considered.