*note the "green blip and the red dip" for healthy vegetation
 

Reflectance (%) differs depending on which wavelength is considered. Different surfaces, atmospheric constituents and lighting geometry will influence the light that is measured by satellites as well as by photographic systems. Knowledge of this behavior enables scientists to make inferences from know absolution profiles, also called "spectra", and perform classification. Aerial photography responds to a very narrow range of visible wavelengths, knowledge of the absorption characteristics different surfaces, i.e. wetlands vs. oak woodland, can help with interpretation and identification. ..