Ground reflectance measurement techniques: a comparison.
The relative accuracies of reflectance factor measurement methods involving the simultaneous, as compared to the sequential, measurement of irradiance on and radiance reflected from the target are discussed. Data are presented to support a statistical demonstration that the simultaneous measurement technique is the more accurate.
Bidirectional Calibration Results for 11 Spectralon and 16 BaSO4 Reference Reflectance Panels
Abstract Eleven Spectralon 1 (a sintered polytetrafluoroethylene-based material) and 16 BaSO4 reference reflectance panels were calibrated using a field calibration technique. The Spectralon panels differed both in their directional/hemispherical and directional/directional reflectance. However, the differences were sufficiently small that “general” calibration equations were developed. For panels constructed of the same material and with the same methods as those used in these experiments, the directional/directional reflectance may be within ± 0.020 at 10°, ± 0.015 at 45°, and ± 0.041 at 80° of that predicted by the “general” equations. For field measurements, these values are considerably better than those that would be obtained using a value of the directional/hemispherical reflectance. The directional/directional reflectance of the 16 BaSO4 panels varied considerably among panels, so much so that it was not feasible to develop “general” calibration equations. Apparently, the nonlambertian properties of BaSO4 panels are dependent upon the method of applying the barium sulfate coating.
Optical reflection properties of natural surfaces
Measurements of the optical reflection characteristics of various natural sands and soils at wavelengths of 4920 A, 6430 A, and 7960 A are presented. It is shown that there is a strong dependence of the intensity and degree of polarization of the reflected radiation on angle of incidence of the radiation, azimuth and elevation angles at which the surface is viewed, wavelength of the radiation, and physical state of the surface itself. A comparison of these measurements with those of other authors shows that the reflectance values obtained here are generally similar to those obtained by Krinov under similar conditions, but the degree of polarization of radiation reflected from the various sands is considerably less than the polarization values observed by Dollfus for sand.