Locating buried drainage pipes is a difficult task confronting farmers and land improvement contractors, especially in the Midwest U.S., where the removal of excess soil water using subsurface drainage systems is a common farm practice. Enhancing the efficiency of soil water removal on land containing a functioning subsurface drainage system typically involves installing new drain lines between the old ones. Before this approach can be attempted, the older drain lines have to be mapped. Previous research supports the feasibility of using ground penetrating radar (GPR) to find buried agricultural drainage pipes. However, one aspect of GPR drainage pipe location and assessment needing further investigation is the GPR pipe response effects associated with GPR antenna orientation relative to drainage pipe directional trend.
A field research study was carried out at a specially designed test plot to evaluate the effect on GPR drainage pipe detection caused by the antenna-to-pipe orientation. Antenna orientations perpendicular and parallel to drain lines were tested using 250 MHz antennas. The GPR data were collected under moderately dry and very wet soil conditions. Overall study results indicated that there can be substantial differences in the strength of the GPR drainage pipe response for an antenna orientation perpendicular to a drain line versus an antenna orientation parallel to a drain line. Under moderately dry soil conditions, a GPR antenna orientation perpendicular to the drain line provided the best GPR drainage pipe response. Conversely, under very wet soil conditions, a GPR antenna orientation parallel to a drain line provided the best GPR drainage pipe response. Consequently, the findings indicated that on-site assessment of soil moisture conditions and knowledge of general drain line directional trend can guide the GPR system antenna set-up and formulation of a GPR survey plan to improve GPR drainage pipe detection and assessment capabilities.