Furrow Microrelief Influence on the Directional Hyperspectral Reflectance of Soil at Various Illumination and Observation Conditions

This paper describes the results of an experiment designed to investigate the effects of furrow microrelief on the soil hyperspectral directional reflectance collected at various illumination and observation conditions. The reflectance of four soil surfaces formed by the same sandy material, one smooth and the others with furrows of different depth, were measured by a laboratory prototype goniometric spectral device. The most notable effects of the furrows on the hyperspectral bidirectional reflectance factor of the surfaces were observed along the vertical plane perpendicular to their furrows at high view zenith angles (as degrees from the nadir), particularly if the light-source zenith angle θ_s is extremely high, and its beams reach the furrows at the horizontal angle of 90°. It was also found that the absorption features of the soil material used in the experiment, located at around 1420 nm, become less visible with the increase of the θ_s, independent of the shape of the surfaces.