Ground reference data are important for understanding and characterizing angular effects on the images acquired by
satellite sensors with off-nadir capability. However, very few studies have considered image-based soil reference data for
that purpose. Compared to non-imaging instruments, imaging spectrometers can provide detailed information to
investigate the influence of spatial components on the bidirectional reflectance distribution function (BRDF) of a mixed
target. This research reported in this paper investigated soil spectral reflectance changes as a function of surface
roughness, scene components and viewing geometries, as well as wavelength. Soil spectral reflectance is of particular
interest because it is an essential factor in interpreting the angular effects on images of vegetation canopies. BRDF data
of both rough and smooth soil surfaces were acquired in the laboratory at 30° illumination angle using a Specim V10E
imaging spectrometer mounted on the University of Lethbridge Goniometer System version 2.5 (ULGS-2.5).
The BRDF results showed that the BRDF of the smooth soil surface was dominated by illuminated pixels, whereas the
shaded pixels were a larger component of the BRDF of the rough surface. In the blue, green, red, and near-infrared
(NIR), greater BRDF variation was observed for the rough than for the smooth soil surface. For both soil surface
roughness categories, the BRDF exhibited a greater range of values in the NIR than in the blue, green, or red. The
imaging approach allows the characterization of the impact of spatial components on soil BRDF and leads to an
improved understanding of soil reflectance compared to non-imaging BRDF approaches. The imaging spectrometer is an
important sensor for BRDF investigations where the effects of individual spatial components need to be identified.