It is possible to use remotely sensed data to distinguish properties of objects because objects have their own spectral signatures. A course inspection of the reflectance of objects using albedo as a measurement shows that different type of land cover reflects different proportion of the incident electromagnetic energy. A fine inspection of the reflectance of objects using spectral reflectance curve show that not only the total energies (that are integrated over the spectral frequency) reflected by objects are different but also the energy at each wavelength interval. This allows the type of condition of an object to be specifically identified. (Supichai, 1994)

The basic concept of remote sensing depends on the fact that all objects on the earth reflect scatters or emits energy. Thus, two main points has been concerned, which are (i) the proportion of electro-magnetic radiation reflected, absorbed, transmitted and backscatter varying in different earth features, as well as different environmental condition. And (ii) the wavelength dependency. Remote sensing is classified into three types with respect to the wavelength regions; (1) Visible and Reflective Infrared Remote Sensing; (2) Thermal Infrared Remote Sensing; (3) Microwave Remote Sensing, as shown in Figure

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