Scattering from Earth Surface Features

Abstract

Remote sensing depends upon measuring the reflection or scattering of incident energy from earth surface features; emission from a surface is also possible, but that is beyond the scope of the discussion in this chapter. If the incident energy is in the optical range of wavelengths – i.e. in the visible or near infrared – it is scattered largely by the surface of the material being imaged. Sometimes there is penetration into a medium, such as short wavelengths into water, but by and large the energy received by an optical sensor reflects from surfaces. Because the wavelength of the microwave energy used in radar remote sensing is so long by comparison to that used in optical sensors1, the energy incident on earth surface materials can often penetrate so that scattering can occur from within the medium itself as well as from the surface. Indeed, there are several mechanisms by which energy can scatter to the sensor, and they can be quite complex. In order to be able to interpret radar imagery it is necessary to have an understanding of the principal mechanisms so that received energy can be related to the underlying biophysical characteristics of the medium.