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

Authors: Allred, Barry; EASH, NEAL - University Of Tennessee; FREELAND, ROBERT - University Of Tennessee; Martinez, Luis; WISHART, DEBONNE - Central State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2017
Publication Date: 12/4/2017
Publication URL: http://handle.nal.usda.gov/10113/5883119
Citation: Allred, B.J., Eash, N., Freeland, R., Martinez, L.R., Wishart, D. 2017. Effective and efficient agricultural drainage pipe mapping with UAS thermal infrared imagery: a case study. Agricultural Water Management. 197:132-137.

Interpretive Summary: Due to both economic and environmental considerations, there is an important need for the development of better methods to map subsurface drainage systems in agricultural landscapes. Surveys carried out by unmanned aircraft systems (UAS) with visible (VIS), near infrared (NIR), and thermal infrared (TIR) sensors could be an effective and efficient way to map agricultural drainage pipes. For preliminary evaluation purposes, UAS surveys with VIS, NIR, and TIR sensors were conducted on June 12, 2017 at a central Ohio (U.S.A) farm field test site that was chosen in part because of available knowledge and documentation regarding the existing subsurface drainage system. Prior to the UAS surveys, a rain gauge and two soil water/temperature sensors were installed to monitor the soil surface. During the two hours the UAS surveys were carried out, 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 OC) and the ground was partially covered with past growing season crop residue and existing early growth stage corn/soybeans. The UAS survey with the VIS and NIR sensors was not successful detecting drainage pipes; however, 60% of the drain lines were found on imagery obtained from the UAS-TIR survey. Consequently, when field conditions are fairly dry, TIR imagery may be better suited for delineating drainage pipe locations than VIS or NIR imagery. Drainage pipe detection from UAS surveys with VIS and NIR sensors is likely to be much better under more optimally wetter field conditions. Therefore, the goal for future research will be to develop guidelines as to when and where UAS VIS, NIR, and/or TIR imagery can be successfully employed to map agricultural drainage pipes, which will require the evaluation of VIS, NIR, and TIR imagery under different soil wetness/dryness conditions at a number of test sites having different types of soil and drainage system characteristics.

Technical Abstract: Effective and efficient methods are needed to map agricultural subsurface drainage systems. Visible (VIS), near infrared (NIR), and/or 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 OC), 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.