Soil moisture content estimation using ground-penetrating radar reflection data

Ground-penetrating radar (GPR) is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves. However, little is known about the exact cause of GPR reflections because few studies have coupled wave theory to petrophysical data. In this study, a 100- and 200-MHz GPR survey was conducted on aeolian deposits in a quarry. Time-domain reflectometry (TDR) was used to obtain detailed information on the product of relative permittivity (er) and relative magnetic permeability (lr), which mainly controls the GPR contrast parameter in the subsurface. Combining TDR data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr. Synthetic radar traces, constructed using the TDR logs and sedimentological data from the lacquer peels, were compared with the actual GPR sections. Numerous peaks in erlr, which are superimposed on a baseline value of 4 for dry sand, are caused by potential GPR reflectors. These increases in erlr coincide with the presence of either organic material, having a higher water content and relative permittivity than the surrounding sediment, or iron oxide bands, enhancing relative magnetic permeability and causing water to stagnate on top of them. Sedimentary structures, as reflected in textural change, only result in possible GPR reflections when the volumetric water content exceeds 0AE055. The synthetic radar traces provide an improved insight into the behaviour of radar waves and show that GPR results may be ambiguous because of multiples and interference.

/pdf/identifying-causes-of-ground-penetrating-radar-reflections-g7dpjncvpc.pdf

Identifying causes of ground‐penetrating radar reflections using time‐domain reflectometry and sedimentological analyses

http://www.lucabaradello.it/carcione/CSG03.pdf

Acoustic and electromagnetic properties of soils saturated with salt water and NAPL

In 1995 and 1996, researchers associated with the US Air Force’s Phillips and Armstrong Laboratories took part in an extensive geophysical site characterization of the Groundwater Remediation Field Laboratory located at Dover Air Force Base, Dover, Delaware. This field experiment offered an opportunity to compare shallow‐reflection profiling using seismic compressional sources and low‐frequency ground‐penetrating radar to image a shallow, unconfined aquifer. The main target within the aquifer was the sand‐clay interface defining the top of the underlying aquitard at 10 to 14 m depth. Although the water table in a well near the site was 8 m deep, cone penetration geotechnical data taken across the field do not reveal a distinct water table. Instead, cone penetration tests show a gradual change in electrical properties that we interpret as a thick zone of partial saturation. Comparing the seismic and radar data and using the geotechnical data as ground truth, we have associated the deepest coherent event in...

/pdf/seismic-reflection-and-ground-penetrating-radar-imaging-of-a-26ockhb30k.pdf

Seismic reflection and ground‐penetrating radar imaging of a shallow aquifer

Particle swarm optimization (PSO) is a relatively new global optimization approach inspired by the social behavior of bird flocking and fish schooling. Although this approach has proven to provide excellent convergence rates in different optimization problems, it has seldom been applied to inverse geophysical problems. Until today, published geophysical applications mainly focus on finding an optimum solution for simple, 1D inverse problems. We have applied PSO-based optimization strategies to reconstruct 2D P-wave velocity fields from crosshole traveltime data sets. Our inversion strategy also includes generating and analyzing a representative ensemble of acceptable models, which allows us to appraise uncertainty and nonuniqueness issues. The potential of our strategy was tested on field data collected at a well-constrained test site in Horstwalde, Germany. At this field site, the shallow subsurface mainly consists of sand- and gravel-dominated glaciofluvial sediments, which, as known from several boreho...

Crosshole traveltime tomography using particle swarm optimization: A near-surface field example

Crosshole seismic tomography and borehole logging for engineering site characterization in Sikeston, MO, USA

Environmental site assessment usually includes determining the geologic character of the subsurface after contamination has occurred. However, at the Groundwater Remediation Field Laboratory (GRFL), we acquired extensive geophysical and geotechnical data before planned contaminant releases happened. These prespill geophysical images provide background data for comparison with data acquired in the future. Additionally, a large amount of cone penetrometer (CPT) data provide in situ geotechnical measurements to compare with surface geophysics.

/pdf/site-characterization-at-the-groundwater-remediation-field-1jkypmeuc9.pdf

Steven J. Cardimona

Papers

Seismic reflection and ground‐penetrating radar imaging of a shallow aquifer

Crosshole seismic tomography and borehole logging for engineering site characterization in Sikeston, MO, USA

Site characterization at the groundwater remediation field laboratory