ABSTRACT
This chapter provides the fundamentals necessary for understanding the techniques and applications of remote sensing. Remote sensing is based on the utilisation of emission and reflection properties of electromagnetic radiation, which carries energy and propagates without attenuation in vacuum but is more or less absorbed in different media. The solar radiation constitutes the external source of energy for the Earth. The atmosphere re-emits part of the radiation received, which contributes to increase the value of the flux measured by the sensor. The accuracy of surface temperatures thus determined from satellite data is difficult to evaluate without choosing homogeneous zones of sufficient size so as to include many pixels. The Doppler Effect produces a shift in frequency between the wave emitted by a moving source and a receiver, due to relative motion between the source and the receiver. In a radar system, the source and the receiver are almost at the same place.
