The evolution of reflectance factors of 16 wheat plots (four different cultivars with four different planting dates) was monitored during the growing cycle using a high spectral resolution radiometer (1024 spectral bands between 468 and 1064 nm). The position of the inflexion point on the red edge of the reflectance curves of plants (between 670 and 760 nm) and the “red slope” (between 580 and 660 nm) give specific information on the leaf area state and percent ground coverage. Results also show that a spectral resolution of 5 nm is adequate to observe the described phenomena. Spectra have also been used to simulate and interrelate different broad spectral bands. The possibility of estimating the reflected photosynthetic active radiation, from SPOT visible channels, is discussed. We conclude that high spectral resolution gives additional information compared with classical measurement performed with broad band radiometers.