Vegetation can become stressed or less healthy because of a change in a range of environmental
factors. These factors include lack of water, concentration of toxic elements/herbicides and
infestation by insects/viruses. The spectral reflectance of vegetation changes according to the
structure and health of a plant. In particular, the influence of chlorophyll in the leaf pigments
controls the response of vegetation to radiation in the visible wavelength. As a plant becomes diseased, the cell structure of a plant alters and the spectral signature of a plant or plant
community will change.

The maximum reflection of electromagnetic radiation from vegetation occurs in the near infrared
wavelengths. Vegetation has characteristically high near-infrared reflectance and low red
reflectance. Air-borne scanners using narrow spectral bands between 0.4 urn and 0.9 urn can
indicate deteriorating plant health before a change in condition is visible in the plant itself.