Important Considerations for Locating Buried Agricultural Drainage Pipe Using Ground Penetrating Radar

Enhancing the efficiency of soil water removal on land already containing a subsurface drainage system typicallyinvolves installing new drain lines between the old ones. However, the older drainage pipes need to be located before thisapproach can be attempted. In ongoing research, a near-surface geophysical method, ground penetrating radar (GPR), hasbeen successful in locating on average 72% of the total amount of drainage pipe present at 13 test plots in southwest, central,and northwest Ohio. The effective use of GPR for drainage pipe detection requires careful consideration of computerprocessing procedures, equipment parameters, site conditions, and field operations, all of which were thoroughly investigatedin this study. Application of a signal saturation correction filter along with a spreading and exponential compensation gain functionwere the computer processing steps most helpful for enhancing the drainage pipe response exhibited within GPR images ofthe soil profile. GPR amplitude maps that show the overall subsurface drainage pipe system required additional computerprocessing, which included 2-D migration, signal trace enveloping, and in some cases, a high frequency noise filter and aspatial background subtraction filter. Equipment parameter test results indicate that a 250-MHz antenna frequency workedbest, and that data quality is good over a range of spatial sampling intervals and signal trace stacking. In regard to the siteconditions present, shallow hydrology, soil texture, and drainage pipe orientation all substantially influence the GPRresponse. Additionally, drainage pipe that are as small as 5 cm (2 in.) in diameter can be detected. However, the fired clayor plastic material of which the drainage pipe is comprised does not appear to have much of an impact. Finally, with respectto GPR field operations, bidirectional surveys offer the best chance for finding all the buried drainage pipe possible, and fordisplaying a subsurface drainage system on an amplitude map, the narrower the spacing between GPR measurement lines,the better the result. Although it is important to note that the amplitude maps generated with a wider spacing between GPRmeasurement lines, still provided plenty of useful data on drainage pipe location. The information supplied by this study canbe employed to formulate guidelines that will enhance the potential of success for using ground penetrating radar in locatingburied agricultural drainage pipe.