One possibility that can be studied to characterize distant targets is to consider the change of the polarization state that a scatterer may induce to an incident wave. Consequently, it is possible to infer some information of the scatterer under consideration considering the properties of the scattered electromagnetic wave with respect to the incident wave, which is basically the transmitted wave by the radar. The way this energy is reradiated depends on the properties of the incident wave, as well as on the scatterer itself. The energy of the incident wave interacts with the scatterer, and as a result part of this energy is reradiated to the space. The radar system transmits an electromagnetic wave, with a given polarization state, that reaches the scatterer of interest. Although this characterization is important when a radar system is considered, as it transmits and receives electromagnetic waves, nevertheless, the interest is on the scattering process itself. The previous section was concerned with the characterization and the representation of the polarization state of an electromagnetic wave. Given two vectors a and b, they are considered orthogonal if they verifyįull size table 1.1.2 Scattering Polarimetry This process is referred to as change of polarization basis or polarization synthesis. The advantage of this representation is that the electric wave is decomposed in a pair of orthogonal polarization states, so it is possible, through a deterministic transformation, to obtain the electric wave for any other pair of orthogonal polarization states. Indeed, this representation must be extended in the sense that any electromagnetic wave propagating in an infinite, lossless, isotropic media can be decomposed as the sum of two orthogonal elliptically polarized waves. Therefore, it is possible to consider that the total electromagnetic wave results from the sum of two orthogonal linear polarized waves. Separately, the electromagnetic wave of each component can be considered as linearly polarized. For an electromagnetic wave that is propagating in the \( \hat \) may be decomposed as the sum of two orthogonal components. The generation, the propagation and the interaction with matter of the electric and the magnetic waves are governed by Maxwell’s equations (Balanis 1989). 1.1.1.1 Electromagnetic Waves and Wave Polarization Descriptors This concept collects the topic of inferring the properties of a given target, from a polarimetric point of view, given the incident and the scattered polarized electromagnetic waves. The second part introduces the concept of scattering polarimetry. As a result, the first part presents the so-called wave polarimetry that deals with the representation and the understanding of the polarization state of an electromagnetic wave. This section summarizes the main theoretical aspects necessary for a correct processing and interpretation of the polarimetric information. Polarimetry refers specifically to the vector nature of the electromagnetic waves, whereas radar polarimetry is the science of acquiring, processing and analysing the polarization state of an electromagnetic wave in radar applications.
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