Department of Agroecology, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark.
Department of Biosystems and Agricultural Engineering, Michigan State University, East Lansing, MI 48824, USA.
Sensors (Basel). 2021 Apr 15;21(8):2800. doi: 10.3390/s21082800.
Agricultural subsurface drainage systems are commonly installed on farmland to remove the excess water from poorly drained soils. Conventional methods for drainage mapping such as tile probes and trenching equipment are laborious, cause pipe damage, and are often inefficient to apply at large spatial scales. Knowledge of locations of an existing drainage network is crucial to understand the increased leaching and offsite release of drainage discharge and to retrofit the new drain lines within the existing drainage system. Recent technological developments in non-destructive techniques might provide a potential alternative solution. The objective of this study was to determine the suitability of unmanned aerial vehicle (UAV) imagery collected using three different cameras (visible-color, multispectral, and thermal infrared) and ground penetrating radar (GPR) for subsurface drainage mapping. Both the techniques are complementary in terms of their usage, applicability, and the properties they measure and were applied at four different sites in the Midwest USA. At Site-1, both the UAV imagery and GPR were equally successful across the entire field, while at Site-2, the UAV imagery was successful in one section of the field, and GPR proved to be useful in the other section where the UAV imagery failed to capture the drainage pipes' location. At Site-3, less to no success was observed in finding the drain lines using UAV imagery captured on bare ground conditions, whereas good success was achieved using GPR. Conversely, at Site-4, the UAV imagery was successful and GPR failed to capture the drainage pipes' location. Although UAV imagery seems to be an attractive solution for mapping agricultural subsurface drainage systems as it is cost-effective and can cover large field areas, the results suggest the usefulness of GPR to complement the former as both a mapping and validation technique. Hence, this case study compares and contrasts the suitability of both the methods, provides guidance on the optimal survey timing, and recommends their combined usage given both the technologies are available to deploy for drainage mapping purposes.
农业地下排水系统通常安装在农田上，以排出排水不良土壤中的多余水分。传统的排水测绘方法，如瓦片探测器和沟渠设备，既费力又容易造成管道损坏，而且在大空间尺度上应用往往效率低下。了解现有排水网络的位置对于理解增加的淋溶和场外排水排放以及在现有排水系统内改造新的排水管道至关重要。最近在非破坏性技术方面的技术发展可能提供了一种潜在的替代解决方案。本研究的目的是确定使用三种不同相机（可见光、多光谱和热红外）和探地雷达（GPR）采集的无人机（UAV）图像在地下排水测绘中的适用性。这两种技术在使用、适用性和测量特性方面具有互补性，并在美国中西部的四个不同地点进行了应用。在 Site-1，整个场地的 UAV 图像和 GPR 都同样成功，而在 Site-2，UAV 图像在场地的一个部分成功，而 GPR 在 UAV 图像未能捕捉到排水管道位置的另一个部分中证明是有用的。在 Site-3，在裸地条件下使用 UAV 图像寻找排水管道的效果较差或没有效果，而使用 GPR 则取得了良好的效果。相反，在 Site-4，UAV 图像成功，而 GPR 未能捕捉到排水管道的位置。尽管 UAV 图像似乎是一种有吸引力的农业地下排水系统测绘解决方案，因为它具有成本效益并且可以覆盖大面积的农田，但结果表明 GPR 作为一种测绘和验证技术来补充前者的有用性。因此，本案例研究比较和对比了这两种方法的适用性，提供了关于最佳调查时间的指导，并建议在两种技术都可用于排水测绘目的的情况下，联合使用这两种技术。
