Radar imaging, as understood here, involves target recognition, i.e. the determination of the detailed properties of an object (size, shape, structure and composition, and also location and speed) from radar echoes returned by it. Advanced approaches are required for this, and several of recent interest are discussed in this book. They include mathematical inverse-scattering techniques based on the solution of integral equations; use of the singularity expansion method (SEM), related to the resonance scattering theory (RST), in which the pattern of resonance-frequency location in the complex frequency plane can be employed to characterize a given radar target; and the use of polarization information. Finally, the measurement of radar cross-sections is described.

A comprehensive overview of the basic principles of radar polarimetry is presented. The relevant fundamental field equations are first provided. The importance of the propagation and scattering behavior in various frequency bands, the electrodynamic foundations such as Maxwell's equations, the Helmholtz vector wave equation and especially the fundamental laws of polarization are presented in the first section. Main poins are the polarization Ellipse, the polarization ratio, the Stokes Parameter, and the Stokes and Jones vector formalisms as well as its presentation on the Poincare sphere and on relavent map projections. The Polarization Fork descriptor and the associated van Zyl polarimetric power density and Agrawal polarimetric phase correlation signatures are introduced also in order to make understandable the polarization state formulations of electromagnetic waves in the frequency domain. The different relevant matrices, the respective terms like Jones Matrix, S-matrix, Muller M-matrix, Kennaugh K-matrix, etc. and its interconnections are defined and described together with change determined for the coherent and partially coherent cases, respectively. Concludes with worked examples and references for further reading.