Using ground penetrating radar (GPR) with multiple pass scans to improve 3D positional reliability of subterranean features

Abstract

The use of Ground Penetrating Radar (GPR) has increased enormously over the past 25 years. One application for GPR that has gained popularity is the detection and location of underground utilities and subterranean features in the first few metres below the ground surface. GPR typically uses frequencies in the range 30MHz to 1GHz. Signals are transmitted into the ground and radiate out in all directions in most solid materials. A fraction of the signal is reflected back by planar, point or linear features. The receiving antenna in the GPR collects the reflected signals. Current practice is to establish an X Y grid and perform a series of scans along each axis. The scans are then compiled into a 3D model.One of the limiting factors with GPR is in the interpretation of the outputs. The accuracy of the 3D model relies on the positional accuracy of the GPR scan paths,the number of scans, and the frequency used. This project examines the benefits of scanning at extra angles in addition to the traditional X and Y directions. Specifically X + 45º and Y + 45º scans are investigated. A test site containing various objects has been prepared. The location of all the target objects has been surveyed, prior to burying the objects. The test site was scanned using a variety of scanning patterns. 3D models were produced from different combinations of the GPR scans. The derived position of the objects from the different 3D models is compared against the surveyed positions. An error analysis on a selected target in the test pit has provided comparison of a number of methods of compiling the 3D model. The additional 45º scans when quantitatively analysed have improved vertical accuracy, but horizontal accuracy is decreased.