Evaluating GPR polarization effects for imaging fracture channeling and estimating fracture properties

This study investigates the polarization properties of GPR signals for imaging flow channeling in a discrete fracture. In particular this study examines if cross-polarized components could be used to image channels in a horizontal fracture. To understand how the polarization of radar waves affects imaging of channelized flow in a horizontal fracture, i) a series of numerical forward models was created with varying fracture aperture, channel orientation, and varying fracture water electrical conductivity, and ii) mulitpolarization field data were used to monitor dipole flow saline tracer tests in a subhorizontal fracture. Numerical modeling demonstrated that the cross-polarized data held useful information about channels but only when the channel is oriented oblique to the E-W wavefield orientation. When the channel is oriented oblique to survey line, summation of the cross-polarized and co-polarized components results in an accurate representation of the total scattered energy from the channel. When the channel is oriented parallel or orthogonal to survey line summation the co-polarized components represent the total scattered energy. In addition to numerical modeling multipolarization, time lapse GPR field data was acquired at the Altona Flat Rock test site in New York State. These surveys were conducted under varying artificial hydraulic gradients, to investigate channeled transport of different concentrations of saline tracer through the fracture and to highlight flow channels between wells. Amplitude analysis of the cross-polarized components reveals flow channeling in an E-W orientation which suggests good well connectivity in that direction. N-S amplitude trends suggest poor hydraulic connectivity. In conclusion, this investigation reveals that cross-polarized components of GPR signals contain useful information for imaging channeled flow in fractured media

Radar Sub-surface Sensing for Mapping the Extent of Hydraulic Fractures and for Monitoring Lake Ice and Design of Some Novel Antennas.

Hydraulic fracturing, which is a fast-developing well-stimulation technique, has greatly expanded oil and natural gas production in the United States. As the use of hydraulic fracturing has grown, concerns about its environmental impacts have also increased. A sub-surface imaging radar that can detect the extent of hydraulic fractures is highly demanded, but existing radar designs cannot meet the requirement of penetration range on the order of kilometers due to the exorbitant propagation loss in the ground. In the thesis, a medium frequency (MF) band sub-surface radar sensing system is proposed to extend the detectable range to kilometers in rock layers. Algorithms for cross-hole and single-hole configurations are developed based on simulations using point targets and realistic fractured rock models. A super-miniaturized borehole antenna and its feeding network are also designed for this radar system. Also application of imaging radars for sub-surface sensing frozen lakes at Arctic regions is investigated. The scattering mechanism is the key point to understand the radar data and to extract useful information. To explore this topic, a full-wave simulation model to analyze lake ice scattering phenomenology that includes columnar air bubbles is presented. Based on this model, the scattering mechanism from the rough ice/water interface and columnar air bubbles in the ice at C band is addressed and concludes that the roughness at the interface between ice and water is the dominate contributor to backscatter and once the lake is completely frozen the backscatter diminishes significantly. Radar remote sensing systems often require high-performance antennas with special specifications. Besides the borehole antenna for MF band subsurface imaging system, several other antennas are also designed for potential radar systems. Surface-to-borehole setup is an alternative configuration for subsurface imaging system, which requires a miniaturized planar antenna placed on the surface. Such antenna is developed with using artificial electromagnetic materials for size reduction. Furthermore, circularly polarized (CP) waveform can be used for imaging system and omnidirectional CP antenna is needed. Thus, a low-profile planar azimuthal omnidirectional CP antenna with gain of 1dB and bandwidth of 40MHz is designed at 2.4GHz by combining a novel slot antenna and a PIFA antenna.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120674/1/wujf_1.pd

GPR Method for the Detection and Characterization of Fractures and Karst Features: Polarimetry, Attribute Extraction, Inverse Modeling and Data Mining Techniques

The presence of fractures, joints and karst features within rock strongly influence the hydraulic and mechanical behavior of a rock mass, and there is a strong desire to characterize these features in a noninvasive manner, such as by using ground penetrating radar (GPR). These features can alter the incident waveform and polarization of the GPR signal depending on the aperture, fill and orientation of the features. The GPR methods developed here focus on changes in waveform, polarization or texture that can improve the detection and discrimination of these features within rock bodies. These new methods are utilized to better understand the interaction of an invasive shrub, Juniperus ashei, with subsurface flow conduits at an ecohydrologic experimentation plot situated on the limestone of the Edwards Aquifer, central Texas. First, a coherency algorithm is developed for polarimetric GPR that uses the largest eigenvalue of a scattering matrix in the calculation of coherence. This coherency is sensitive to waveshape and unbiased by the polarization of the GPR antennas, and it shows improvement over scalar coherency in detection of possible conduits in the plot data. Second, a method is described for full-waveform inversion of transmission data to quantitatively determine fracture aperture and electromagnetic properties of the fill, based on a thin-layer model. This inversion method is validated on synthetic data, and the results from field data at the experimentation plot show consistency with the reflection data. Finally, growing hierarchical self-organizing maps (GHSOM) are applied to the GPR data to discover new patterns indicative of subsurface features, without representative examples. The GHSOMs are able to distinguish patterns indicating soil filled cavities within the limestone. Using these methods, locations of soil filled cavities and the dominant flow conduits were indentified. This information helps to reconcile previous hydrologic experiments conducted at the site. Additionally, the GPR and hydrologic experiments suggests that Juniperus ashei significantly impacts infiltration by redirecting flow towards its roots occupying conduits and soil bodies within the rock. This research demonstrates that GPR provides a noninvasive tool that can improve future subsurface experimentation

Multi-band and dual-polarised ultra-wide band horn antenna for landmine detection using ground penetrating radar technique

Anti-Personnel (AP) and Anti-Vehicle (AV) landmines are considered as a problem of global proportions and it is estimated that about 60-70 million landmines are scattered within at least 70 countries all over the world. Many of the landmines are made with minimum metal content so that certain detection methods, such as metal detectors, often tend to fail. A promising concept for the detection of buried non-metallic objects is Ground Penetrating Radar (GPR). Although GPR has shown some promising results, the diversity and complexity of the problem inflict certain challenges on the operation of GPR systems. The investigations discussed in this thesis cover important aspects of GPR with particular focus on design of a new Ultra-Wideband (UWB) antenna. A systematic approach is adopted to show the GPR modelling process, and understanding the fundamental principles of GPR technology. The resolution of GPR highlights the importance of operating bandwidth. RF characterisation of materials is another aspect of GPR that will be addressed by the measurement of the relative permittivity of the materials. A novel multifunctional, multi-channel antenna design is proposed to enable the investigation of multiband imaging technique in GPR. The antenna is fabricated and the experimental measurements verify the performance of the designed antenna. The GPR results of 3D printed landmine models and real landmines in various environmental conditions have confirmed, the detection capability of the designed antenna. The GPR results of the landmines have also been investigated to study characteristic signatures of the landmines under certain system parameters