Effective and efficient agricultural drainage pipe mapping with UAS thermal infrared imagery: A case study

Effective and efficient methods are needed to map agricultural subsurface drainage systems. Visible (VIS), near infrared (NIR), and thermal infrared (TIR) imagery obtained by unmanned aircraft systems (UAS) may provide a means for determining drainage pipe locations. Preliminary UAS surveys with VIS, NIR, and TIR sensors were carried out at a farm field test site in central Ohio (U.S.A). During the UAS surveys, the soil surface was very dry (less than 5 mm of rainfall the previous week, soil surface volumetric water content below 16%, and soil surface temperature above 33 °C), and the ground was partially covered with past growing season crop residue and existing early growth stage corn/soybeans. Under these field conditions, drainage pipes were not detected with the VIS and NIR imagery. Conversely, the TIR image detected roughly 60% of the subsurface drainage infrastructure known to be present. Consequently, TIR imagery from UAS surveys was found to have considerable potential for drainage pipe mapping purposes, and compared to VIS and NIR imagery, may be better suited for detecting drain line locations under dry surface conditions. However, more evaluation of VIS, NIR, and TIR imagery for drainage pipe mapping is certainly needed under different soil wetness/dryness conditions and at a number of test sites having different types of soil and drainage system characteristics.