Deterministic Deconvolution Of Ground-Penetrating-Radar Data At A Limestone Quarry

Abstract

A 30 m by 30 m two-dimensional grid was designed on a flat bench behind a quarry face of predominantly limestone with thin shale layers located at a Bonner Springs, Kansas site to test the utility of ground-penetrating radar (GPR) for stratigraphic studies. GPR data were collected along seven lines parallel to the quarry face and seven lines perpendicular to the quarry face, each separated by 5 m, using 50 MHz, 100MHz, 200 MHz, and 400 MHz antennas. As a part of the project, confirmation of reflection events, ringing suppression, and velocities of electromagnetic (EM) wave propagation in the limestone were studied. GPR instrument wavelets were successfully collected in the air. With a known GPR instrument wavelet, ringing in GPR data was significantly suppressed by a deterministic deconvolution. The validity of using a wavelet acquired in air as the operator for deterministic deconvolution was shown in the real-world application of a radar system with 400 MHz antennas to a quarry site consisting of interbedded limestones and shale partings. A total of 78 horizontal holes were drilled in key locations on three exposed quarry faces where data were acquired before and after conductive steel rods, 1.5 m in length, were placed in the holes. Diagnostic GPR responses from the horizontal steel rods serve as known reflectors. The steel rods provide critical information for: 1) confirmation and nature of specific geologic reflection events in the GPR data, 2) GPR resolution limits, 3) accuracy of velocities calculated from common-midpoint data, and 4) identification of multiples. The effectiveness of suppressing ringing waveforms suggests that the deterministic deconvolution of GPR data with the GPR instrument wavelet in the air should be included as a standard GPR data processing step.