Fracture imaging in sandstones using high resolution ground penetrating radar

Ground penetrating radar (GPR) is a technique that employs radar waves to survey subsurface geological or man-made structures. In this survey, a high resolution, high frequency Pulse EKKO 1000 system using operating frequencies of 225, 450 and 900 MHz was used to detect subsurface structural and sedimentological features in the Triassic sandstones of Thurstaston Common, Wirral, England. The Pulse EKKO 1000 system is essentially a continuous profiling system where transducers are moved across a survey line at approximately constant velocity. Measured fix points are appended to the profile as surveying takes place. The mode of operation for the survey was single fold, fixed offset, reflection profiling and a typical 20 m survey line at Thurstaston generated about 2 megabytes of data. An estimation of radar wave velocity versus depth was made from a common mid point method (CMP) where the direct ground wave gave a radar wave velocity of 0.08 nsec per metre for the Triassic sandstones. Digital GPR data require considerable editing and processing to produce a final image. Processing techniques widely used in seismic data processing were adapted for use in the processing of radar profiles. All data display and processing was achieved using Pulse EKKO software running on a 486 personal computer