Under typical field conditions of green vegetation over a dark soil, vegetation indices have been shown to vary in a near-linear fashion with the fraction of absorbed photosynthetically active radiation (APAR). On the basis of model results the AVHRR/2 sensor, which was not designed originally to make biophysical measurements, provides the best match to criteria for producing a near-linear variation of vegetation indices with APAR. The radiance measured by the AVHRR/2 sensor, however, is highly sensitive to atmospheric conditions. In the near future sensors will be launched which have been designed with biophysical imaging as an important criterion. This letter examines the potential of three of these new sensors for estimating APAR. Scattering coefficients calculated for each sensor are shown to provide poor simulation of the pholosyn-thetic action efficiency of photosynthesis. Using the combined visible wavebands to calculate the scattering coefficients, however, produce values that are comparable with AVHRR/2.