Termografia con drone
Immagine termografica di una persona. Immagine tratta da pixabay.com libera per usi commerciali - Autore byrev
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The drone for thermal imaging analysis

The thermal imaging with drone has made significant progress over the past two years. There are numerous proposals for professional thermography services with drones. However it is good to know its limits and potential for a correct and profitable use of this science.

Thermal imaging – Writing of heat

The word Thermography (or themal imaging) derives from the union of two terms: ϑερμός (hot) e γραφία (writing), and it means heat writing. Thermography is part of the Non Destructive Testing (N.D.T.), as it does not alter the structure of the objects.

Therefore, the purpose of Thermography is to acquire the mapping of the heat of the objects or their thermogram.

Areas of Thermography

Thermal imaging nvestigations are aimed at identifying certain problems of objects and artefacts in the civil and industrial sector. Thermography therefore lends itself well to identifying problems related to thermal bridges, water infiltrations, and operating anomalies in solar panels, electrical panels, etc.

Thermal imaging analysis

To fully understand the potential and limitations of drone thermography, it is good to briefly describe the “terrestrial” and “aerial” thermographic investigations.

Purpose of “terrestrial” Thermography

Thermography captures the radiation (or in more trivial terms of heat), an object or part of it. The tool with which to capture the radiation, which we remember is not visible to the naked eye, is the Thermal Camera..

It is a camera with a particular sensor capable of capturing the irrigation of a body. In order to provide useful indications, captured images – thermograms – must also be interpreted with the use of dedicated software. Based on the analysis of the heat mapping, it is therefore possible to identify the cause of a specific problem.

“Aerial” thermographic analysis

Termocamera ZENMUSEXT-DJI
Thermal camera ZenmuseXt-DHI – Source DJI website

Thermal imaging analysis with drone  work in a similar way to terrestrial ones. The only exception is that the camera is on board the drone and is controlled remotely. Also in this case it is essential to capture significant images for the purpose of the investigation. Given that the capture of the thermograms takes place in flight, the thermal imager must be well stabilized

 

 

Pixels – “Soul” of Thermal imaging analysis

The factor that influences terrestrial and aerial thermography is essentially the resolution of the thermal imager. In fact, pixels are the discriminating factor for obtaining significant thermograms for identifying the problem being analyzed. A thermal imager with a low resolution e.g. 60×80 pixels will provide a low resolution image (480 pixels). A thermal imaging camera with a resolution of 240 x 320 pixels will instead provide a high resolution image (76,800 pixels), and therefore more readable.

For more details on the features of a drone thermal camera, we recommend reading the article  “Professional Payloads – Read the specs” from the Blog.

Drones and Thermography – On-board instrumentation

Dji-mavic 2 Thermo
DJI Mavic 2 Thermo – Source DJI website

The on-board instrumentation for making drone thermography is therefore made up of the Thermal Camera and its energy source. In addition to being stabilized, the thermal imaging camera must be fully remotely manageable. Therefore the need for native software or an App for FPV management (see glossary) is fundamental. In addition, it is important to bear in mind that the need for simultaneous acquisition of images from the visible (photo / video), and infrared is a fundamental aspect for thermographic analysis.

It is therefore clear that it is not possible – at present – to do Thermography with a 300gr drone. There are still no cameras so light and with such a thermal resolution that they can be mounted on a 300gr or 250gr drone.

Drone requirements for thermographic analysis

In order to provide a realistic view of the possible use of the drone for thermographic analyzes it is good to analyze the requirements that the drone must have as a tool for thermography.

Flight time

Even if today the flight time, with an appropriate set of spare batteries and a flight planner, is somewhat manageable, it remains critical for Thermography. In fact, objective conditions, such as solar radiation or the presence of thermal gradients, in particular conditions and for certain types of analysis can vary substantially in limited time intervals. In order to be able to carry out a good thermographic analysis with drone it is good to:

  • have the right flight capacity, in term of time, considering that a survey on a building facade or on a photovoltaic field can take two hours or more;
  • carefully plan the surveys, taking into account that some flights may have to take place in conditions of less than optimal light.

Payload

The use of drones for thermographic analysis is currently limited by the payload of the drone. In fact, the thermal imaging camera and its system, in addition to being able to be allocated appropriately, must comply with the MTOW (see glossary), envisaged for the drone in use. It is therefore preferable that a drone for thermography is born for this type of activity. Opting for a drone with a non-native thermographic solution can be limiting.

Flight restrictions

Regardless of the payload, the objective limitations imposed by the legislation on the flight of a drone in an urban area, highlight a very binding limit to the use of the drone for thermographic analysis.

Type of the activities – Be careful on the reports produced with the drone

If the thermographic analysis is carried out in the context of an expert report (CTP – Partial Technical Consultancy or ATP – Preventive Technical Assessment), it is essential to know that your equipment must be certified and calibrated. Therefore the availability of both the certificates of conformity and calibration of the Thermal Camera and of the other on-board auxiliary instruments, and possibly of the drone itself, is a must to avoid seeing the expertise invalidated.

Power of drone thermography

The requirements of a drone for thermography clearly indicate that the drone as a tool for thermographic analysis can be considered valid in certain well-defined areas: in the maintenance of photovoltaics and in the analysis of facades.

Solar panels maintenance

Drone thermography finds concrete application in preventive and corrective maintenance on photovoltaic panels.

The analysis of the operation of the arrays of panels placed in the photovoltaic fields, for the identification of both micro fractures, and of degradation and broken connection between cells, is immediate. In this case the drone allows to carry out surveys with lower cost, in less time and with excellent results. The flight in non-urban areas, the geometry of the panel arrays, the diagnostic simplicity, the possibility of automating the survey, are all factors in favor of aerial surveys with drone, compared to manual terrestrial surveys.

Buildings-Facade analysis

Termografia Facciata
Building facade thermography – Created by the author November 2011

Another field of application of drone thermography is that of the analysis of building facades. In fact, the presence of detachments of facade elements such as plaster, tiles, face-view bricks, can be detected by a thermal imaging camera on board a drone. The consequence of detachment is therefore highlighted as an area at a different temperature compared to the context. Accessibility at heights where only the basket (with high costs) would allow for a survey, privileges the use of the drone. However considering the limitations imposed by the legislation in urban areas, this activity is feasible in peripheral areas and on isolated buildings such as farmhouses, villas and farmhouses.

Flight Planner – Mandatory tool for drone thermography

Droneharmony Flightplanner
DroneHarmony Flight planner – Source DroneHarmony website

Thinking to carry out professional thermography with drone, without using a good flight planner, is unthinkable. By their very nature, thermographic measurements require careful planning. The analysis of a panel string or that of a building facade can be planned and optimized with the use of a flight planner.

In fact, the software will optimize the flight of the drone, in relation to the extension to the analysis area.

 

Conclusions

Drone thermography is certainly an interesting technique that is suitable for very well defined cases. A drone designed for Thermography is something that must be considered by those who wish to apply this technique in their business. But it is good to remember that a drone “adapted” to thermography does not match the needs of this type of non-destructive analysis.


Note regarding the images: Some of the images shown in the article are taken from the websites of DJI and Drone Harmony. Each image still mentions the source. The image of the facade’s thermogram was created by the author. The use of the images is exclusively for the purpose of a better understanding of the contents of the article. The highlighted image is taken from the pixabay.com site, free for commercial use and the author is byrev.

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Last Updated on/Ultimo aggiornamento – 28/07/2020

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