Chapter 26: Composite Moveout Correction to a Shallow Mixed Reflection/Refraction GPR Phase
J. F. Hermance, R. W. Jacob, R. N. Bohidar, 2010. "Composite Moveout Correction to a Shallow Mixed Reflection/Refraction GPR Phase", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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Adapting elements that are common to exploration seismology and electromagnetic wave propagation is extremely useful for interpreting ground-penetrating-radar (GPR) data in a variety of forms, whether the application is environmental, geotechnical, agricultural, or archaeological. In many regions of the world, subsurface conditions are such that material nearest the surface has a low GPR velocity and is underlain by material that has a higher GPR velocity. This condition leads to a critically refracted GPR phase from the higher-velocity interface at depth. Such refracted phases might be particularly troublesome when one is routinely interpreting conventional GPR profiling data as reflections, if in fact the critical distance for refractions is less than the fixed transmitter-receiver offset used for the profile. Misinterpreting such a phase might lead to a subtle, even significant error in depth estimates if only the standard normal-moveout (NMO) correction is applied. However, a complementary wide-angle common-midpoint (CMP) or common-shotpoint (CSP) “calibration” sounding allows identification of such a phase and application of a simple composite moveout correction. The procedure can be illustrated with data from a stratified glacial-drift site in southeastern New England.
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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.