Directional reflectance of light from landscapes on a long transect in Australia – forest to desert

The reflectance of land and vegetation observed in satellite imagery depends on sun and viewing geometry. This bidirectional reflectance requires correction for monitoring changes in vegetation cover and condition. We used a digital camera mounted in a light aircraft, and fitted with a fisheye lens, to measure directional reflectance of a diverse range of landscapes along a long transect in Australia — between Brisbane and the Simpson desert. All, except one, of the measured directional reflectances were able to be characterised accurately (adjusted r² > 0.95) by the product of two analytical functions. The first, $G\left({\theta }_1,{\theta }_2\right)$, which represents volume scattering, is a function of illumination and viewing zenith angles, ${\theta }_{1}and{\theta }_2$, and has one parameter $k$: