GPR Signature Research Articles

GPR Signatures of Pipes and Walls with Emphasis on the Effect of Inclined Scanning Trajectory

This study investigates the effects of some commonly encountered constraints such as inclined scanning trajectory, multiple targets in the vicinity and material variation on GPR responses of pipes and walls. Further, the effects of wall inclination and broken walls are also explored in GPR signatures. Interpretation of such signatures in GPR data for archaeological and geotechnical surveys has been a challenge. A physical model was created to simulate buried pipes and walls under controlled conditions by maintaining density and moisture content of the soil medium. The presence of PVC pipes, plastered brick and stone walls buried in the dry sand have been investigated and major observations have been reported. The inclined scanning trajectory on buried pipes shows a change in curvature of hyperbola-like signatures. Inclined transects near the ends of pipes and walls manifest single limb GPR signatures. The responses of multiple pipes and walls show dependence on separation of targets and footprint of an antenna. One can discern stone walls from brick walls by recognizing the diffraction of waves by irregular stones in GPR responses. The signatures of walls differ from pipes with respect to the width of the apex and variation in the intensity in the limb.

Ground penetrating radar geologic field studies of the ejecta of Barringer Meteorite Crater, Arizona, as a planetary analog

AbstractGround penetrating radar (GPR) has been a useful geophysical tool in investigating a variety of shallow subsurface geological environments on Earth. Here we investigate the capabilities of GPR to provide useful geologic information in one of the most common geologic settings of planetary surfaces, impact crater ejecta. Three types of ejecta are surveyed with GPR at two wavelengths (400 MHz, 200 MHz) at Meteor Crater, Arizona, with the goal of capturing the GPR signature of the subsurface rock population. In order to “ground truth” the GPR characterization, subsurface rocks are visually counted and measured in preexisting subsurface exposures immediately adjacent to and below the GPR transect. The rock size‐frequency distribution from 10 to 50 cm based on visual counts is well described by both power law and exponential functions, the former slightly better, reflecting the control of fragmentation processes during the impact‐ejection event. GPR counts are found to overestimate the number of subsurface rocks in the upper meter (by a factor of 2–3x) and underestimate in the second meter of depth (0.6–1.0x), results attributable to the highly scattering nature of blocky ejecta. Overturned ejecta that is fractured yet in which fragments are minimally displaced from their complement fragments produces fewer GPR returns than well‐mixed ejecta. The use of two wavelengths and division of results into multiple depth zones provides multiple aspects by which to characterize the ejecta block population. Remote GPR measurement of subsurface ejecta in future planetary situations with no subsurface exposure can be used to characterize those rock populations relative to that of Meteor Crater.

GPR detection of buried steel gas cylinder; a study conducted in a sandbox

In this study a controlled medium was created to apply the ground penetrating radar technique to detect and locate a buried steel gas cylinder. The work was to demonstrate the utility of the GPR in locating underground utilities prior to excavation for civil works. The survey was carried out in a sandbox which measures 4.20 m by 2.30 m of surface cross section and has a depth of 1.10 m. The wooden box with an open bottom was filled with dry sand which had previously been sieved to rid it of organic matter and therefore to create a substantially homogenous medium. An empty LPG cylinder was buried in the sand at a measured location and depth from the sand surface. The measurement was carried out with the 800 MHz shielded GPR antennae. The experiment led to a definition of the GPR signature of the horizontally oriented empty steel cylinder. The burial depth, representing the top surface of the cylinder from the sand surface was found to be in the range of 0.58 to 0.64 m, compared with a concealed depth of 0.60 m. The bottom of the sandbox was also well imaged and located within the range of 0.95 m to 1.20 m. the actual depth of the sand was 1.10 m.

GPR signatures of temperate and cold land ice

GPR signatures of temperate and cold land ice

Spatial mapping of multi-year superimposed ice on the glacier Kongsvegen, Svalbard

AbstractGround-penetrating radar (GPR) and satellite ERS-2 synthetic aperture radar (SAR) are used to map the thickness and extent of the superimposed ice (SI) zone on the surge-type glacier Kongsvegen, Svalbard. GPR imagery shows sub-horizontal SI layers lying unconformably above a discrete boundary. Below this boundary, the ice has a GPR signature similar to that of ice further down-glacier in the ablation zone. This boundary is posited to represent the closing of crevasses that were created during the last surge of Kongsvegen in ∼1948. Open crevasses would have interrupted the formation of sheet layers of SI due to efficient vertical drainage of the snowpack. Aerial photographs suggest that the crevasses closed sometime in the period 1956–66. A classified SAR image from 2003 is used to delineate the extent of the SI zone. The SI extent in the SAR image agrees well with the SI zone mapped by GPR. Using the SI spatial depth distribution, we estimate the mean annual accumulation of superimposed ice to be 0.16 ± 0.06 m w.e. a−1 (locally up to 0.43 m a−1 w.e.). This corresponds to ∼15–33% of the local winter balance and ∼5–10% of the total winter balance measured since 1987.

Sustainable urban development and geophysics

Sustainable urban development and geophysics

4-D ground penetrating radar monitoring of a hydrocarbon leakage site in Fortaleza (Brazil) during its remediation process: a case history

A 4-D monitoring GPR survey was carried out in order to outline the light non-aqueous phase liquid (LNAPL) plume underground during a remediation process in the area of an impacted gas station in Fortaleza, NE Brazil. The complex GPR signature of the plume was well characterized. Low reflectivity zone corresponds to hydrocarbon vapor phase in the vadose zone. Enhanced reflections are associated with free and residual products directly above the water table. A theoretical model based on geochemical zonation of the LNAPL was calculated using a finite difference time domain (FDTD) forward modeling code, whose synthetic radargrams provide useful insight into the nature of the reflection events related to LNAPL contamination. Hydrogeologic and hydrochemical data from installed monitoring wells provided additional support for interpreting of the GPR response. Moreover, a network of radar sections collected during fifteen months at the polluted site show clearly temporal changes in the plume dimensions, induced by regular pumping of groundwater. This corrective action caused an important drop of the water table that was followed by a rapid shrinking of the impacted area in the vadose zone, generating pooling of vapor products. A steady restore of the reflectivity in the shadow zone suggests a decrease of LNAPL saturation along the GPR survey.