Factors affecting the spectral response of forest canopies: A review

Interpreting remote sensing data on forest canopies demands an adequate knowledge of factors affecting their optical properties. After a short analysis of the optical properties of a forest canopy, a review of the factors acting on the forest reflectance is presented. These factors can be external or internal. The five external factors considered are: size of the viewed area, orientation and inclination of the view axis, sun elevation, nebulosity and wind speed. Three internal factors can also affect forest reflectance: row orientation (for young artificial forests), optical properties of the background (soil and understory), and canopy geometry. The effects of these different factors are analysed and discussed.