Principles of Modern Radar - Volume 2 1891121537

622 CHAPTER 13 Introduction to Radar Polarimetry13.6 SUMMARYWave polarization and polarimetry play vital roles in radar target identification comprisingthe three phases of target detection, discrimination, and recognition. This chapter presentsan introduction to radar polarimetry emphasizing the polarization behavior as describedby the scattering matrix. After a brief review of linear, circular, and elliptical polarizationand the geometrical parameters of polarization ellipse, such as tilt and ellipticity anglesand axial ratio, Stokes parameters and scattering matrices are introduced and explainedusing examples on canonical targets. The projection of polarization states on the Poincarésphere is discussed. The transformation of the scattering matrix from one polarization statebasis to another (e.g., linear to circular and vice versa) is derived. Unitary transformationsare applied to the scattering matrix for fully polarized targets and eigen-polarization statescorresponding to maximum and minimum backscattered power are derived. The locationof null polarization states on the Poincaré sphere is discussed, and the Huynen polarizationfork is introduced as a useful tool in the visualization of optimal polarimetric parameters.Stokes reflection or Mueller matrix is derived for partially polarized waves. The distinctionbetween Kennaugh’s and Huynen’s formulations of the target scattering matrix (partiallypolarized case) is discussed. To demonstrate the application of radar polarimetry, the scatteringmatrix measurements of a cone with grooves (resembling a missile reentry vehicle)are processed to extract key features such as specular scattering and edge contributions,and the usefulness of polarimetric signatures to discriminate between coated and uncoatedbodies is discussed. The polarimetric behavior of precipitation clutter, sea clutter,and ground clutter is also discussed. A radar instrumentation setup for scattering matrixmeasurement in block diagram form is described, and implications on the setup imposedby colocation of transmit and receive antennas for monostatic measurements and the needto measure amplitude and phase of each orthogonal channel relative to a coherent sourceare discussed.13.7 FURTHER READINGThis chapter provided an introduction to radar polarimetry based on the original theorydeveloped by Kennaugh [13] and Huynen [14]. Significant modern developments in radarpolarimetry and its application to imaging have been described in the papers, books andmonographs listed below.• Boerner and Lee [60] provide a succinct review of the existing pertinent monographs,books, and study guides on radar polarimetry, and identify particular topics that arebeing covered in new books in order to reflect on complexity of state-of-the-art polarimetricsystems as well as modern evolution of analytical techniques for polarimetrybeyond the seminal methods introduced by Kennaugh.• Boerner, Wolfgang-Martin, Introduction to Synthetic Aperture Radar (SAR) Polarimetry,Wexford Press, April 2007. Available from: http://www.rto.nato.int/abstracts.asp• Yamaguchi, Yoshio, Radar Polarimetry from Basics to Applications: Radar RemoteSensing using Polarimetric Information (in Japanese), IEICE Press, Dec. 2007.• Masonnett, Didier and Souyris, Jean-Claude, Imaging with Synthetic Aperture Radar,CRC Press, Taylor and Francis, 2008.