Ralf Grispen

Thermografisch Adviesbureau

Uden BV

info@thermografie.nl

The Netherlands

Using a helicopter would be the perfect solution as this would give the ability to look at the roof from an optimal vantage. Helicopters do not come cheap however, so a more affordable alternative is to use an unmanned aerial vehicle (UAV) with a built-in thermal imaging camera and test flights have confirmed that this method is a viable solution for roof insulation inspections. With a remote controlled helicopter it is possible to cover the entire building and inspect it from every possible angle so it is a great addition to the regular ground based thermographic inspections.

The UAV used in the test flights is an octocopter which means that it has eight rotors. The Draganflyer X8 uses an onboard processor and eleven onboard sensors (three gyros, three accelerometers, three magnetometers, one barometric sensor, and one GPS receiver) to enable it to stabilize and hover in place. This enables it to serve as a stable platform for camera systems, such as thermal imaging cameras from FLIR Systems.

Tau 320 Thermal Imaging Camera Core

The thermal imaging camera mounted on the UAV is Tau 320. The size of the camera core, without a lens, is 44.5 x 44.5 x 30.0 mm, it weighs just below 72 grams and the power consumption is less than 900 mW. Due to the extremely small size and light weight it has little or no impact on the flight time. Despite the small proportions and low energy consumption, the camera provides excellent quality thermal images with a resolution of 320 × 256 pixels and a thermal sensitivity of below 50 mK (0.05 °C).

The octocopter’s eight electric motors are powered from one LiPo (Lithium-ion Polymer) battery which provides 5400 mAh/14.8 Volt which is enough for about 15 minutes flight time. The thermal footage from the camera is sent wirelessly to the ground station through a 5.8GHz video link and is at the same time recorded by the onboard digital video recorder and stored on a MicroSD memory card.

Thermal Camera Image of roof insulation problems.

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Remote controlled Octocopter with the Thermal Camera.

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The thermal footage from the camera is sent wirelessly to the ground station through a 5.8GHz video link and recorded by the onboard digital video recorder.

Thermal Pattern

The thermal imaging camera core is not radiometric, so unlike thermography cameras it is not calibrated to provide temperature measurements for each pixel in the thermal image which does not mean that it is useless for building inspections. Because exact temperature differences are an important indication of the severity of insulation problems, thermographers would normally prefer to use radiometric thermal imaging cameras for inspections. However with roof inspections a non radiometric thermal image is far better than no thermal image at all. The thermal pattern makes it possible to locate insulation problems but the severity of the problem still needs to be determined.

In one case the aerial inspection with the UAV revealed a serious problem with the roof insulation of a residential care center in the Dutch city of Deventer. The thermal image indicated clearly that there was heat leakage from certain parts of the roof and after locating the problem areas using the UAV and closer investigation inside the building revealed that the builders had actually forgotten completely to put in insulation materials in some locations. This was not only sloppy construction work but it also caused significant energy loss for the residential care center.

Several test flights have proved that this method is an excellent addition to regular ground based thermography. Aerial vantage point give the ability to look at the building from new angles, revealing insulation defects that would be very difficult to detect without the use of a UAV.