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.