Reflectance anisotropy analysis of homogeneous canopies using laboratory and HyMap airborne data

The BRDF (Bidirectional Reflectance Distribution Function) of vegetation canopies exhibits an anisotropic behaviour that is related to illumination and viewing geometries. However, some other aspects such as the optical properties and the structural parameters of the targets should be taken into account for an adequate explanation of the bidirectional phenomenon. The present investigation examines the anisotropic behaviour of the homogeneous canopies reflectance from laboratory data as a function of viewing geometry, structural parameters and optical properties of the samples in order to obtain relevant information to improve biophysical parameters retrieval and discrimination of vegetation canopies from optical spectral data. Airborne data acquired in Daisex-99 campaign over Barrax test site (Albacete/Spain) with the HyMap instrument are also included. The HyMap concept is able to record hot spot effect, and moreover, the different flight tracks carried out in Daisex-99 allow us to complete anisotropic behaviour shown in laboratory experience, where illumination was fixed, with airborne data acquired under different solar zenith angle. Results confirm initial hypothesis that anisotropy reflectance is related to structural parameters of the vegetation and show anisotropic behaviour usefulness to study vegetation canopies increasing data dimensionality, varying both illumination and view angles. The anisotropy factor, ANIF, has resulted a simple relationship to provide us with relevant information about vegetation canopies structure. Keywords- Vegetation Canopies, Anisotropy, Reflectance, Hot Spot, Hymap.