Earth scientists are increasingly attempting to utilize spacecraft observations to measure and predict change in the Earth's surface characteristics and surface-related phenomena, such as climate. The task is not easy. The inherent dynamics in Sun, Earth and space platform orbits, together with a diversity of sensor viewing geometries on existing and future orbiting sensors, result in radiometric data that can be expected to vary independent of changes in the surface properties. Conversely, appreciable changes in consequential surface attributes may not be discernable due to compensatory variations in sunsensor-target geometries coupled with prevailing sky and surface conditions. Thus, field studies to determine the nature and magnitude of the natural surface reflectance and sky irradiance variations and to subsequently improve our ability to interpret satellite data are essential. A unique field radiometer, called the PARABOLA, was developed to accurately measure the multi-directional incoming and outgoing spectral radiances for a variety of earth surface types, ranging from rangeland vegetation to ice and snow. Improvements in computational procedures have been recently developed and 3-D graphics capabilities have been implemented for aiding in the analysis of the directional radiances. Field measurements conducted with the PARABOLA for a variety of surface cover types reveal considerable diversity in the magnitude and character of their directional reflectances, which are complicated further for some vegetation types by seasonal variations and ambient sky conditions. Changes due to solar position under "clear" skies appear to be more predictable, however, such that radiometric correction models may soon be developed for some cover types and condition classifications.