Author
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Allred, Barry |
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Submitted to: Fast Times: News for the Near Surface Geophysical Sciences
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/4/2011 Publication Date: 2/11/2011 Citation: Allred, B.J. 2011. Location and assessment of drainage pipes beneath farm fields and golf course greens using ground penetrating radar: A research summary. Fast Times: News for the Near Surface Geophysical Sciences. 15(4):49-55. Interpretive Summary: Studies indicate that ground penetrating radar (GPR) is a potentially important tool for mapping drainage pipe systems beneath both agricultural fields and golf course greens. For GPR to be successful within agricultural field settings; site conditions, equipment parameters, field survey set-up, and computer processing steps are important considerations. Golf course greens are a particularly good environment for using GPR to detect drainage pipes; however, due to the complex patterns of these drainage pipe systems, and intensive data collection effort is usually required to map the in-place drainage pipe networks. In addition to mapping drainage pipe systems, GPR, given the right circumstances, is also capable of evaluating drain line functionality by detecting whether pipe flow obstructions are present. Continuing research is focused on integration of GPR with real time kinematic Global Positioning System receivers in order to improve the efficiency of drainage pipe detection GPR surveying. Furthermore, investigations are now being carried out to appraise the impact on the GPR drainage pipe response due to GPR antenna orientation relative to drain line trend. Technical Abstract: Enhancing the efficiency of soil water removal, and in turn crop productivity, on farmland already containing a subsurface drainage system, typically involves installing new drain lines between the old ones. However, before this approach can be attempted, the older drainage pipes need to be located. The ability to map drainage pipes can also be important within golf course green settings. Research investigations have found ground penetrating radar (GPR) was successful in locating on average 74% of the total amount of pipe present at fourteen agricultural field test plots in southwest, central, and northwest Ohio. This method worked well finding clay tile and corrugated plastic tubing drainage pipe down to depths of around 1 meter (3 feet) within a variety of different soil materials. Additional research has focused on various factors that can be important for achieving success using GPR to find agricultural field drainage pipes. Results with respect to equipment parameters indicate that choosing the proper antenna frequency is crucial, and antennas with a center frequency of around 250 MHz seem to work best. Also, data quality is similar over a sampling interval range of 2.5 to 10 cm (1 to 4 inches) between points along a measurement line and for averaging 4 to 32 signal traces at a measurement point. In regard to agricultural field site conditions, shallow hydrology, soil texture, and drainage pipe orientation all influence the GPR response. Moist soils with pipes at least partially filled with air provide good GPR field conditions, assuming the radar signal penetrates to the drain line depth. Sandy soils allow greater radar signal penetration than do clayey soils. Field operations (spacing distance between measurement lines and bidirectional vs. unidirectional surveys) along with the algorithms used in the computer processing sequence to generate GPR profiles and GPR maps are all very important considerations. Golf course greens were found to be an extremely good environment for collecting GPR data.A rather wide range of antenna frequencies, from 250 to 1000 MHz, work reasonably well for mapping drainage pipe systems. The lower frequency GPR antennas (250 MHz) are slightly better for locating drainage pipes; however, higher frequency antennas (900 to 1000 MHz) are the best choice if sand/gravel layer thickness determinations are needed in addition to drainage pipe mapping. With regard to field survey operations, due to the complex drainage pipe networks typically present on golf course greens, spacing distances of 1 m or less between adjacent parallel GPR measurement transects are needed and two sets of parallel GPR measurement transects, with the sets perpendicular to one another, are usually required. Finally, GPR has also proven capable of providing information on drainage pipe condition with respect to the presence of water flow obstructions. |
