Credit: Photo by Kevin Price, Kansas State University.
This image illustrates the difference between what a person sees when looking at a soybean plant in the visible spectrum (left), and one of the ways spectral analysis can represent the same plant using wavelengths not visible to the human eye. In this case, the plant on the right is presented using NDVI readings. NDVI is a ratio: (Near Infrared – Red)/(Near Infrared + Red).