Abstract: Vegetation remote sensing data from sensor change with phenologyand the sun altitude angles. Therefore, the optimum temporal images must be selectedfrom different periods for vegetation studies. The season of the greatest vegetationreflection difference in the visible and near-infrared regions is the optimum temporalfor the vegetation classifying studies. The results indicate that the absolute difference and relative difference of plantspecies in reflectance axe the greatest in spring and early summer. Then the greatestnumber of crop types can be identified in the images. The autumn images are most suitable for identifying deciduous leaf vegetation, for the leaf pigments of all kinds appear at that time. Vegetation reflectances in MSS5 and MSS7 decrease with the decrease of the altitude angles of the sun. Therefore, appropriate images of the sun altitude angles must be selected for the study of vegetation. The author concludes that the optimum temporal images of remote sensing for vegetation studies in Hubei Province or north tropics are those taken in April, May and November.

Key words: Plant Spectral curve, Plant phenological change, Optimum temporalimages, Colour infrared aerophotographs