Noninvasive 3D ground-penetrating radar (GPR) imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface. Full-resolution imaging requires unaliased recording of reflections and diffractions coupled with 3D migration processing. The GPR practitioner can easily determine necessary acquisition trace spacing on a frequency-wavenumber (f-k) plot of a representative 2D GPR test profile. Quarter-wavelength spatial sampling is a minimum requirement for full-resolution GPR recording. An intensely fractured limestone quarry serves as a test site for a 100-MHz 3D GPR survey with 0.1 m × 0.2 m trace spacing. This example clearly defines the geometry of fractures in four different orientations, including vertical dips to a depth of 20 m. Decimation to commonly used half-wavelength spatial sampling or only 2D migration processing makes most fractures invisible. The extra data-acquisition effort results in image volumes with submeter resolution, both ...

Full-resolution 3D GPR imaging

Since both the spatial and vertical heterogeneities in soil properties have an impact on crop growth and yield, accurate characterization of soil properties at high sampling resolution is a preliminary step in successful management of soil-water-plant system. Conventional soil sampling and analyses have shown mixed economical returns due to the high costs associated with labor-intensive sampling and analysis procedures, which might be accompanied with map uncertainties. Therefore, the conventional laboratory methods are being replaced or complemented with the analytical soil sensing techniques. The objective of this chapter is to review different soil sensing methods used to characterize key soil properties for management of soil-water-plant system. This will cover laboratory, in situ in the field, and on-line measurement methods. This review chapter is furnished with an overview of background information about a sensing concept, basic principle and brief theory, various factors affecting the output of the sensor, and justification of why specific soil properties can be related with its output. The literature review is succeeded with an integration and analysis of findings in view of application in the precision agriculture domain. Potentials and limitations of current sensor technologies are discussed and compared with commonly used state-of-the-art laboratory techniques. As sensing is commonly addressed as a very technical discipline, the match between the information currently collected with sensors and those required for site-specific application of different inputs, and crop growth and development is discussed, highlighting the most accurate method to measure a soil property for a given application.

Sensing soil properties in the laboratory, in situ, and on-Line: A review

Just a few meters below the Earth's surface lie features of great importance, from geological faults which can produce devastating earthquakes, to lost archaeological treasures. This refreshing, up-to-date book explores the foundations of interpretation theory and the latest developments in near-surface techniques, used to complement traditional geophysical methods for deep-exploration targets. Clear but rigorous, the book explains theory and practice in simple physical terms, supported by intermediate-level mathematics. Techniques covered include magnetics, resistivity, seismic reflection and refraction, surface waves, induced polarization, self-potential, electromagnetic induction, ground-penetrating radar, magnetic resonance, interferometry, seismoelectric and more. Sections on data analysis and inverse theory are provided and chapters are illustrated by case studies, giving students and professionals the tools to plan, conduct and analyze a near-surface geophysical survey. This is an important textbook for advanced-undergraduate and graduate students in geophysics and a valuable reference for practising geophysicists, geologists, hydrologists, archaeologists, and civil and geotechnical engineers.

Near-Surface Applied Geophysics

Ground penetrating radar polarization and scattering from cylinders

Determination of volumetric water content of concrete using ground-penetrating radar

Near-field dipole radiation dynamics through FDTD modeling

Periodic events in ground penetrating radar (GPR) data may result from antenna and target effects rather than reflections from geologic features. One of the most common pitfalls in GPR data interpretation is to identify each event on a radar cross-section as scattering from a discrete horizon, without considering other possible sources of these events. Soil electrical properties and surface roughness affect ground penetrating radar antenna radiation and waveform characteristics. An impedance mismatch occurs over soils with electrical properties different than those for which the antennas were designed to perform optimally over, and results in periodic ring-down, which can be misinterpreted as stratigraphy or multiple reflections. In addition, target resonance can introduce additional periodic features that can lead to misinterpretation in regards to the number of targets present. Co-pole and cross-pole antenna configurations can be combined with polarization dependent scattering characteristics of subsurface objects to recognize and reduce antenna ring-down for improved imaging and interpretation.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000GL008512

Pitfalls in GPR data interpretation: Differentiating stratigraphy and buried objects from periodic antenna and target effects

Crossed dipole (cross-pole) and parallel dipole (co-pole) GPR data were acquired at an industrial site that formerly operated as a creosote wood treating facility in order to locate buried pipes and tanks or other possible contaminant-filled subsurface structures. Cross-pole data are not typically considered during GPR field studies, but proved essential for accurate site characterization at this location, as images produced using co-pole data had a poor signal to noise ratio. Data interpretations were confirmed through exploratory trenching conducted subsequent to this study. The GPR data proved successful in locating back-filled trenches that contained creosote-filled drainage tile, as well as vaults and a pit filled with pure creosote product at the site.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999GL008365

Demonstration of using crossed dipole GPR antennae for site characterization

The focus of this article is to demonstrate through physical model experimentation a potential means for identifying contaminated areas where a light non-aqueous phase liquid (LNAPL) hydrocarbon has been redistributed by a rising water table in a previously hydrocarbon residual-free vadose zone using ground-penetrating radar (GPR). Analogies of the experimentation conducted in this study are situations where a rise of the water table follows leakage from a tank or pipe at depth or where an LNAPL hydrocarbon plume has migrated laterally from a surface source along the top of the saturated zone and a subsequent rise of the water table occurs. Research to date has provided insight into mechanisms that may offer the potential for LNAPL detection under certain field conditions; however, no studies have specifically focused on developing a potential detection strategy for a case in which residual hydrocarbon is present in a water-saturated medium. A tank model filled with gravel and sand was designed to allow GPR measurements to be made on the surface before, during, and after water and gasoline injections and fluctuations within the tank. Background GPR measurements were made initially with only water being raised and lowered in the model, and the water table was then raised and lowered beneath a volume of 219 liters of gasoline that was injected into the bottom of the tank. Measurements from the initial raising and lowering of the water with no gasoline present demonstrate the sensitivity of GPR for monitoring changes in subsurface water content and minor fluctuations of the water table. Measurements made during the raising and lowering of the water table with gasoline in the model show differences from the measurements made when only water was raised and lowered, and a comparison of the data show that reflections in GPR data can be enhanced when residual gasoline is present in a water-saturated system because there is less attenuation of the radar signal. Differences in travel times to subsurface reflections between the two stages of the experiment are also caused by the residual gasoline present in the water-saturated medium. Results of this study provide the basis for a strategy that has the potential for successful detection and delineation of LNAPL hydrocarbon-contaminated areas at field sites where the conditions are similar to those modeled through this experimentation.

Stanley J. Radzevicius

Papers

Ground penetrating radar polarization and scattering from cylinders

Near-field dipole radiation dynamics through FDTD modeling

Pitfalls in GPR data interpretation: Differentiating stratigraphy and buried objects from periodic antenna and target effects

Demonstration of using crossed dipole GPR antennae for site characterization

Residual Hydrocarbons in a Water-Saturated Medium: A Detection Strategy Using Ground Penetrating Radar