A technique used to investigate broad scale phenological events by means of repetitive satellite observations is described. The temporal sequence of leaf development and senescence of deciduous forest and crop canopies is characterized by changes in their reflectance of solar energy at several wavelength intervals. Correlation with simultaneous ground observations is used to develop relationships between normalized reflectivity ratios derived from multispectral satellite data and the areal percentage of green vegetative material present in the canopy. Satellite observations made over a nationwide network of test sites during the years 1972 and 1973, provide estimates of the amount of green canopy present as it developes during the spring season as well as estimates of the percentage of leaf coloration and abscission during the autumnal period.