Virtual surfaces simulating the bidirectional reflectance of semiarid soils

Virtual surfaces of four semiarid soils-regs, crusts, playas and sands-used to predict their bidirectional reflectance in the optical domain are discussed in the paper, on the background of their real equivalents and their directional reflectance characteristics. These surfaces are defined by the horizontal and vertical semiaxes of equal-sized opaque spheroids simulating their particles or aggregates. The spheroids are regularly dispersed into a net of squares of a given side length on a freely sloping plane. They are absorbed into the ground with their tops projecting to a given height above the slope. The material of the vertical structure is additionally defined by its refractive index. Virtual surfaces determined in this way were used as part of the input data to a geometrical model, which predicts the soil surface normalized reflectance (NR), expressed as the ratio of the total radiance of the simulated surface viewed from the off-nadir direction to the radiance viewed from the nadir.