PROCESSING AND INVERSION OF MULTI-OFFSET AND MULTI-AZIMUTH GPR DATA FOR ENVIRONMENTAL AND ENGINEERING APPLICATIONS

摘要

We apply linear and azimuthal multi-fold GPR techniques to study waste disposal sites and areas scheduled for quarry and civil engineering operations. Linear (single azimuth, multiple offsets) and azimuthal (multiple azimuths and offsets) multi-fold GPR data were obtained at four sites with maximum 6000% and 24000% fold for the linear and azimuthal datasets respectively. Pre-stack depth imaging of waste disposal sites provided detailed 3-D reconstructions of soil-waste and waste bedrock contacts. Post-stack migration algorithms successfully imaged quarry and building sites in limestone. Synthetic datasets, obtained by considering homogeneous and isotropic half-spaces, frequency dependent electrical properties of the media and by taking into account attenuation and dispersion effects, were compared with Common Mid Point (CMP) gathers to evaluate properties of subsurface materials. Soil-waste and rock-waste contacts, bedding joints, fractures, cavities and filling materials in limestone were successfully imaged by migrated multi-fold data over 70% of the surveyed area. Results of processing and inversion of GPR data were calibrated by boreholes, excavations and inspections of outcrops and rock faces. An average 2% accuracy was attained in joint mapping at quarry and building sites, where field-synthetic data comparison was exploited to discriminate air/sediments -filled joints and cavities.