This document presents a technical memorandum by NASA on the use of red and photographic infrared linear combinations for monitoring vegetation. The study evaluates the relationships between various linear combinations of red and infrared radiances and experimental plot biomass, leaf water content, and chlorophyll content. The radiance variables evaluated include red and infrared radiances, as well as linear combinations such as the infrared/red ratio, the square root of the infrared/red ratio, the infrared-red difference, the vegetation index (VI), and the transformed vegetation index (TVI). The study also compares these with green and red linear combinations. Regression analysis showed that infrared and red linear combinations were more significant than green and red linear combinations for monitoring vegetation. The VI, TVI, and square root of the infrared/red ratio were the most significant, followed closely by the infrared/red ratio. These linear combinations were found to be sensitive primarily to green leaf area or green leaf biomass. The study concludes that these linear combinations of red and infrared radiances can be used to monitor the photosynthetically active biomass of plant canopies. The study also evaluates the influence of infrared bandwidth on ratio technique applications for estimating canopy variables. It found that the regression significance for different infrared bandwidths was extremely similar when used with red radiances or in various linear combinations. The study also considers phenological considerations, showing that the spectral manifestations of grass canopy phenology can be inferred from the three sampling periods used. The results indicate that the infrared/red ratio and related transformations are sensitive to the amount of photosynthetically active vegetation present in the plant canopy. The study concludes that these linear combinations are superior to green/red ratios for monitoring vegetation.This document presents a technical memorandum by NASA on the use of red and photographic infrared linear combinations for monitoring vegetation. The study evaluates the relationships between various linear combinations of red and infrared radiances and experimental plot biomass, leaf water content, and chlorophyll content. The radiance variables evaluated include red and infrared radiances, as well as linear combinations such as the infrared/red ratio, the square root of the infrared/red ratio, the infrared-red difference, the vegetation index (VI), and the transformed vegetation index (TVI). The study also compares these with green and red linear combinations. Regression analysis showed that infrared and red linear combinations were more significant than green and red linear combinations for monitoring vegetation. The VI, TVI, and square root of the infrared/red ratio were the most significant, followed closely by the infrared/red ratio. These linear combinations were found to be sensitive primarily to green leaf area or green leaf biomass. The study concludes that these linear combinations of red and infrared radiances can be used to monitor the photosynthetically active biomass of plant canopies. The study also evaluates the influence of infrared bandwidth on ratio technique applications for estimating canopy variables. It found that the regression significance for different infrared bandwidths was extremely similar when used with red radiances or in various linear combinations. The study also considers phenological considerations, showing that the spectral manifestations of grass canopy phenology can be inferred from the three sampling periods used. The results indicate that the infrared/red ratio and related transformations are sensitive to the amount of photosynthetically active vegetation present in the plant canopy. The study concludes that these linear combinations are superior to green/red ratios for monitoring vegetation.