Chapter 6: Toward True-amplitude Vector Migration of GPR Data Using Exact Radiation Patterns
J. van der Kruk, R. Streich, M. Grasmueck, 2010. "Toward True-amplitude Vector Migration of GPR Data Using Exact Radiation Patterns", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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The amplitudes and phases of raw ground-penetrating-radar (GPR) data depend on the antenna radiation patterns, the vector nature of electromagnetic (EM) wave propagation, and the EM properties of the subsurface. Migrated GPR data should accurately represent the subsurface EM property contrasts alone. To achieve this, migration algorithms must explicitly account for the radiation patterns and vector wave propagation. A specific vector-migration algorithm models and corrects for exact-field radiation patterns, which include far-, intermediate-, and near-field contributions and propagation effects. When applied to GPR data containing dipping planar reflections, the algorithm produces images largely invariant to the relative orientations of the antennae and reflectors, indicating that most radiation-pattern effects are corrected for. In contrast, strongly orientation-dependent amplitudes and phases in scalar Gazdag and far-field vector images show that these algorithms do not adequately account for radiation-pattern effects. For polarization-dependent features (e.g., most underground utilities), the exact-field vector-migration algorithm produces images with orientation-dependent amplitude variations in qualitative agreement with theoretical expectations, suggesting that the algorithm may serve as a starting point for reconstructing the scattering properties of the targets. In contrast, the scalar Gazdag and far-field algorithms yield distinctly false amplitude variations.
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Near-surface seismology and ground-penetrating radar (GPR) have enjoyed success and increasing popularity among a wide range of geophysicists, engineers, and hydrologists since their emergence in the latter half of the twentieth century. With the common ground shared by near-surface seismology and GPR, their significant upside potential, and rapid developments in the methods, a book bringing together the most current trends in research and applications of both is fitting and timely. Conceptually, near-surface seismology and GPR are remarkably similar, and they share a range of attributes and compatibilities that provides opportunities to integrate processing and interpretation workflows, which makes them a perfect pair to share pages in a book.
With growth in numbers and professional emphasis have come sections, focus groups, and even professional societies specifically promoting near-surface geophysics. The emergence of near-surface geophysics groups, beginning in the late 1990s and extending into the early twenty-first century, has fueled a diversity of opportunities for professional collaborations. A range of workshops and shared publications has been the fruit of collaborative efforts. The near-surface community continues to extend and develop methods and approaches necessary to satisfy increasing demands in some of the socioeconomically pertinent disciplines such as civil and environmental engineering and hydrology. This book represents the first formal cooperative effort undertaken by the near-surface communities of the Society of Exploration Geophysicists, the American Geophysical Union, and the Environmental and Engineering Geophysical Society.