Target Scattering Mechanism in Polarimetric Synthetic Aperture Radar

Target Scattering Mechanism in Polarimetric Synthetic Aperture Radar

Microwave remote sensor can work day and night, and is nearly unaffected by weather and atmospheric conditions. It plays a more and more important role for earth and other planet monitoring in both global and regional scales. As an imaging system, polarimetric synthetic aperture radar (PolSAR) has the ability to obtain fully polarimetric information and becomes one of the mainstreams in microwave remote sensing. Full polarization acquisition greatly enhances radar capability in many aspects and expands its application fields. The studies and applications of polarimetric radar imaging enter a golden era with the significant supports of solid radar polarimetry theory, advanced signal processing techniques, and easily accessible high-quality data sets. Credits are owed to those radar polarimetry pioneers in both fundamental theory and hardware system development.

Based on giants’ shoulders, this book focuses on a branch of radar polarimetry and PolSAR studies: interpretation and application of target scattering mechanism in PolSAR. This research branch is dedicated to bridge the gap between the acquired data and practical applications. Also, it is one of the main challenges in polarimetric radar imaging. This book mainly summarizes our studies, researches, and thoughts of this field in the past decade. Hopefully, it will be benefit for potential readers. This book mainly contains five chapters.

Chapter 1 briefly reviews the basic theories in radar polarimetry, the fundamental principles in polarimetric radar imaging, and some advanced concepts for understanding and interpreting target scattering mechanisms.

Chapter 2 focuses on advanced polarimetric target decomposition development mainly in terms of model-based decomposition. The limitations of classical model-based decomposition are firstly discussed. Meanwhile, a review of recent advances in scattering mechanism modeling and decomposition theorem is presented. Then, a polarimetric-interferometric model-based decomposition is introduced, which is one of several first attempts to fuse both polarimetric and interferometric information to enhance the target decomposition performance. Besides, a general model-based decomposition scheme, which uses all elements of a polarimetric coherency matrix, is presented. The key principles and features include: the double- and odd-bounce scattering models are generalized with their independent orientation angles; each scattering model is considered with equal weight and without any implied assumption of model priority; the unknown model parameters are optimally and simultaneously determined; the occurrence of negative power is theoretically avoided. In addition, the reflection symmetry assumption, branch conditions, and manual interventions are also avoided. Further perspectives for future developments are also discussed.

Chapter 3 introduces the uniform polarimetric matrix rotation theory which aims to investigate target scattering orientation diversity. The underlining physics is that target scattering responses are generally orientation dependent. Although this orientation dependency effect usually leads to scattering mechanism ambiguity and makes PolSAR data modeling and interpretation difficult, target scattering orientation diversity also contains rich information which is seldom considered and explored. Proper exploration of such orientation diversity has the potential to provide valuable insights to reveal intrinsic properties of different targets. The concept of the rotation domain along the radar line of sight is introduced. The core idea is to extend polarimetric matrix at a given imaging geometry to the rotation domain. Then, the uniform representation of each polarimetric matrix element and a new set of oscillation parameters in the rotation domain are derived and summarized. Application demonstrations in terms of land cover classification are carried out.

Chapter 4 introduces the visualization and characterization tool of polarimetric coherence pattern. Complementary to the uniform polarimetric matrix rotation theory introduced in Chap. 3, the developed polarimetric coherence pattern provides solutions to mine and characterize the hidden information between two arbitrary polarimetric channels. A set of new polarimetric features are derived to completely represent those hidden information. Land cover classifications demonstrate the efficiency of these polarimetric features. Furthermore, polarimetric coherence enhancement in the rotation domain is investigated and demonstrated for manmade target extraction and crops discrimination.

Chapter 5 focuses on natural disaster damage investigation by exploring multi-temporal PolSAR data using fully polarimetric techniques. The study case is the great tsunami induced by the earthquake of March 11, 2011, which occurred beneath the Pacific off the northeastern coast of Japan. Two authors, Si-Wei Chen and Motoyuki Sato, experienced this destructive disaster and carried out field investigations afterward. In this chapter, the polarimetric scattering mechanism changes pre- and post-event are examined in theory and confirmed by advanced model-based decomposition and polarization orientation angle techniques. Then, damage indexes are proposed and their relationships to real damage levels are disclosed and established. A rapid urban damage level mapping technique is developed therein which has the capability to simultaneously and automatically identify urban damage locations and damage levels for a huge monitoring area. Finally, other damage condition investigations in terms of flooded river area and flooded paddy field are also carried out.

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