Development of a georadar system for three-dimensional imaging of the subsurface and its application to studies of crystalline rock bodies

To produce accurate images of complex subsurface geology using ground-penetrating radar, the high standards of 3-D reflection seismic imaging used in the hydrocarbon exploration industry had served as a role model. The aim has been to produce more reliable interpretations of georadar data in order to foster the application of georadar in engineering geology. Fractured crystalline rock was chosen as the medium for evaluating acquisition and processing techniques applied to georadar subsurface imaging. The RAD-SEIS system was developed for the efficient acquisition of high-density georadar data. High production rates in the field were achieved by recording georadar signals continuously at walking speed at 0.05 m spatial intervals with ±0.1% antenna positioning precision. Software written and implemented on a portable 486 computer controlled the acquisition and the 16-bit digitization of the radar signals. By recording the radar data in a standard seismic format and automatically generating survey geometry files, field data could be accessed directly by reflection seismic processing software. In the granitic gneiss of the Gotthard Pass of Switzerland, horizontal and steep fracture were imaged with 100 MHz antennae to depth of 60 m. A comparison of migrated constant-offset sections with trace spacings of 0.05m and 0.25m showed steep fractures to be better defined on the high-density dataset. Fourteen-fold multi-offset profiling delivered continuous velocity information and better definition of deep reflectors. Application of 3-D ground-penetrating radar in engineering geology was tested in a dimension stone gneiss quarry of southern Switzerland. (author) figs., tabs., refs