ANALYZING THE SPECTRAL DIMENSIONALITY OF OUTDOOR VISIBLE AND NEAR-INFRARED ILLUMINATION FUNCTIONS

The spectral properties of outdoor illumination functions can vary sig nificantly, owing to atmospheric conditions and scene geometry. Using a statistical analysis of a comprehensive physical model, we show that the variation in outdoor illumination functions over both the visible range (0.33-0.7 mu m) and the visible/near-infrared range (0.4-2.5 mu m) can be represented accurately by use of seven-dimensional linear m odels. The physical model includes solar and scattered radiation as we ll as the effects of atmospheric gases and aerosols. The MODTRAN 3.5 c ode was employed for computing radiative transfer aspects of the model . We show that the new model has strong agreement over the visible wav elengths with the empirical study of Judd et al. [J. Opt. Sec. Am. 54, 1031 (1964)]. We also demonstrate the accuracy of the model over the 0.4-2.5-mu m spectral range, using measured outdoor illumination funct ions. (C) 1998 Optical Society of America. [S0740-3232(98)01311-8]. OC IS codes: 010.0010, 150.2950, 280.0280, 330.1690.