Agricultural drainage tile surveying using an unmanned aircraft vehicle paired with Real-Time Kinematic positioning-A case study

A 2012 agricultural census reported approximately 218,000 U.S. farms to have subsurface tile networks that artificially drain over 19.7 million hectares. These drainage networks present a significant expense to land-owners during their installation, inspection, maintenance, and upgrading. The conventional methods for locating buried drain tiles are by excavation employing heavy machinery and hand tile probes which are expensive and time-consuming. Aerial photography offers promise as a less-expensive alternative for mapping tile networks over vast acreages. In aerial photography, ground-surface discoloration from the concentratio of draining moisture periodically appear directly atop functioning drains. We have noted drainage surface patterns occurring on Midwestern fields with minimal surface residue one to three days following significant rainfall. An unmanned aerial vehicle (UAV) equipped with visible or thermal infrared (TIR) imaging can detect these distortions at appropriate times. Our study compared Real Time Kinematic (RTK) and Wide Area Augmentation System (WAAS) Global Positioning System (GPS) for mapping of subsurface drain tiles. The case study revealed WAAS GPS provided insufficient accuracy and precision for physically locating the buried tiles. Although more expensive and complicated, satellite RTK technology increases the vertical and horizontal alignment of UAV surveys as it projects aerial imagery precisely and accurately onto a geodetic coordinate system. The pairing of RTK technology with the UAV survey was deemed essential for physically locating buried tile lines in the field.