The observed rise of the concentration of carbon dioxide over the last 30 years has intensified interest in the study of the global carbon cycle. The key role of vegetation in this cycle is clearly demonstrated by the semi–annual variations of the carbon dioxide concentration in a given hemisphere. The primary variables of interest are the net primary productivity and the biomass on a global scale and the key to their estimation is the leaf-area index (LAI). A global determination of the LAI is practical only with remote-sensing satellite systems. A hierarchical approach to obtaining a LAI map of deciduous boreal forests, which contain a significant part of the total global carbon reservoir using satellite data is presented. The results show that it is very important to understand the nature of the basic physical interaction of solar radiation with canopy biophysical characteristics, if meaningful estimates of these variables are to be made. This understanding has been achieved using ground, helicopter and aircraft measurements made very near to the area covered by the LANDSAT satellite.