Variations in the spectral radiometric function, measured in the field, of five different types of terrain as a function of atmospheric conditions, solar altitude, and viewing position

The purpose of this experiment was to: 1. Determine how closely five different types of terrain, such as sand, cultivated soil, grass, loose rocks, and bushes resembled Lambertian surfaces. 2. Determine how closely the radiometric functions for three wave length bands compared for each type of terrain. 3. Develops the shape of the radiance envelope as defined by the radiometric function for each type of terrain. 4. Determine the effect of changes in solar altitude on the radiometric function. 5. Determine the effect of changing the conditions of irradiance from clear sky to overcast sky on the radiometric function. The experimental procedures used for measuring the magnitude of the radiance vectors were adequate to yield results from which the radiometric function can be determined, but the variability was higher than predicted. Even with this variability, which was expected in this type of experiment, the results were still significant enough at 95% confidence to yield valuable guidance to scientists and engineers. The five types of terrain tested were concluded to be generally non-Lambertain, and the radiometric functions were entirely a function of atmospheric conditions, solar altitude, and viewing position due to the peculiar scattering patterns for each type of terrain. The radiometric functions were independent of wavelength, except for several isolated cases. Furthermore, they were unsymmetrical for clear sky irradiance and symmetrical for an overcast sky. An approximation of the shape of t h e radiance envelope in two planes and the magnitude of the radiance vectors are presented in the results to help the reader visualize the effects of the input variables