Using drones to locate drainage pipes

Research from Aarhus University, US universities and research organisations has investigated the use of drones for locating drain pipes. Drainage pipe installations are often poorly documented, which is problematic when they need to be retrofitted or repaired. Researchers from Department of Agroecology at Aarhus University have, together with a group of American colleagues, investigated the possibility of using drone imagery in the search for the hidden drainage system.

Risk of destroying the drainage pipes

“Until now the preferred methods have been tile-probing and trenching to locate the drainage pipes. But this is very time-consuming, and the risk of destroying the drainage pipes is huge. We have looked into using ground penetrating radar (GPR), but it is a very expensive and impractical solution to use for large areas,” says PhD student Triven Koganti from Department of Agroecology at Aarhus University.

Mapping drainage system

“With the advent of drone technology and increase in affordability of cameras, we have new opportunities to explore their applications in agriculture. Mapping the drainage system of the field is one such application, which is neither time-consuming nor expensive,” says Triven Koganti.

In trying to map drainage systems with drones, the researchers have worked with three different camera systems to find the most reliant one.

1. Visible-color (VIS-C)
2. Multispectral (MS)
3. Thermal Infrared (TIR)

Difference in soil moisture content and temperature

According to Triven Koganti, directly above the drainage pipes, the soil is often drier than the soil between the drainage pipes, which is especially evident just after it has rained. “Sometimes after it has rained you will be able to see the difference between the dry soil and the wet with the visible-color and multispectral cameras. And you will also be able to capture it with the thermal infrared camera, because the soil warms up at different speeds depending on whether it is dry or wet. The soil directly on top of the drainage pipes will have a different temperature and would appear as a linear feature on the thermal infrared images.”

_{Text continues underneath image}

As part of his PhD study, Triven Koganti has worked with scientists from the U.S. Department of Agriculture and other American organisations. Together they have investigated the possibility of using drone imagery to locate drainage pipes in the fields. – Photo: Triven Koganti

Great potential for using drones to locate drainage pipes

According to Koganti, the studies show that there is great potential for using drones to locate drainage pipes in the field. “However it’s not a silver bullet,” he says. The success rate for the three different cameras and measurement methods is not 100%. For the three types of cameras, the researchers found the following success rates:

• Visible-color (VIS-C) – 48%
• Multispectral (MS) – 59%
• Thermal Infrared (TIR) ​​- 69%

Generate a highly accurate digital terrain model

For that reason, the researchers suggest using all three cameras if possible when measuring in the field. Koganti explains that they had some examples where they were are able to find the pipes by using multispectral cameras, but not with the other two cameras, and vice versa.

Also, by generating high-resolution imagery using a VIS-C camera, a farmer can generate a highly accurate digital terrain model, which is useful information for drainage contractors.

Combining with GPR technology

“We also suggest combining with GPR technology, where you can pinpoint the location and depth of the pipes down to a few centimeters, while the positional accuracy of, for example, our thermal infrared measurements can be 4 meters without accurate georeferencing”, says Koganti.