"Radiation that is not absorbed or scattered in the atmosphere can reach and interact with the Earth's surface. There are three (3) forms of interaction that can take place when energy strikes, or is incident (I) upon the surface.
These are: absorption (A); transmission (T); and reflection (R). The total incident energy will interact with the surface in one or more of these three ways. The proportions of each will depend on the wavelength of the energy and the material and condition of the feature. Absorption (A) occurs when radiation (energy) is absorbed into the target while transmission (T) occurs when radiation passes through a target. Reflection (R) occurs when radiation
""bounces"" off the target and is redirected. The reflectance R is defined by the ratio of reflected radiant power to incident radiant power. The transmittance T of a medium is defined by the ratio of transmitted radiant power to incident radiant power. The absorptance A of a medium or target is defined by the ratio of absorbed radiant power to incident radiant power. Conservation of energy require that, at a certain wavelenght: R+T+A=1. To express the circumstance that the reflection can occurre in different direction as the surface deviates from a specular one, becoming rough the concept of surface scattering has been introduced. However, the concept of scattering concerns mainly atmopheric interaction with ELM and radar systems."