What is thermal imaging? What is infrared imaging?
Thermal Imaging sensors are commonly referred to terminology such as thermal camera, temperature camera, heat vision camera, infrared camera, thermal imaging sensor, heat signature camera, and even thermal heat vision sensor. In this post we will refer to this type of imaging as infrared or thermal imaging. All objects (above absolute zero) emit infrared energy as a function of its temperature. Infrared energy is generated by the vibration of atoms and molecules. The higher the temperature of an object, the faster its molecules and atoms move. This movement is emitted as infrared radiation which our eyes cannot see but our skin can feel. Thermal imaging is the use of a special infrared camera sensors to illuminate a spectrum of light invisible to the naked eye. Thermal energy is invisible to the naked eye and works in different ways; it can be emitted, absorbed, or reflected. Infrared cannot see through objects but can detect differences in radiated thermal energy between materials. This is known as thermal bridging or heat transfer. To sum it all up thermal imaging cameras are precise non-contact temperature measurement devices.

inside infrared camera diagram

How does thermal imaging work? Answers Infrared radiation coming from a scene is focused onto an infrared sensor detector. From there it is processed into the visible light spectrum which our eyes can see. As a result, thermal images can look different depending on how the thermal image is reproduced in the visible spectrum. The different ways in which the colors are reproduced color palette used. Typical go-to color palette options include black hot, white hot, fusion, and ironbow.

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What infrared (thermal) drone camera resolution (640 vs 336) should I get?

FLIR thermal drone cameras come in a variety of options, the most popular are the DJI Zenmuse XT and XT2 these cameras come in two resolution options, 336×256 and 640×512 pixels. Which resolution you need is dependent on your use case. For basic inspection, the 336×256 should be enough to identify basic faults and temperature differences. For search and rescue, wildlife management, or other public safety use cases we suggest the 640×512 as it gives a larger field of view.

What lens should I get for the Zenmuse XT or XT2? / Does resolution and lens configuration have an impact on the infrared image? 

In this section we will be talking about the cameras field of view (FOV). FLIR’s thermal cameras come in two resolution options: 640×512 and 336×256. These cameras come in 9mm,13mm,19mm, and 25mm lens options. Please note that these lenses are fixed and cannot be interchanged such as in a DSLR camera. The lens option and camera resolution will impact the FOV. The table below illustrates this. To have a better understanding of the FOV we included a diagram to show this instead of just degrees.

To go one step further we wanted to give an example with how the FOV from the 336 with a 9 mm lens can look very similar to the 640 with a 19 mm lens. The difference is infrared accuracy at a specific point. The industry standard is to use a 3×3 pixel spot size to ensure infrared precision. Notice how the 3×3 spot size on the 336 camera when flying at 200 feet is 1.3 feet versus the 6.44 inches on the 640 camera. With the higher resolution, per pixel of data is much greater this is extremely important especially if the infrared camera is being used for search and rescue.

flir xt infrared camera comparison

What’s the difference between the performance and radiometric DJI Zenmuse XT or DJI Zenmuse XT2?

The performance version is best when only trends in temperature are needed. The performance version can read temperature but only at the center 4 pixels of the screen. This is known as the spot meter. The DJI Zenmuse XT2 is not available in the performance version, radiometric only. The radiometric version allows the user to get a temperature reading from any of the pixels in the field of view. For FLIR thermal imaging cameras the radiometric version is denoted with ‘R’ at the end of its product title. An example is the FLIR Vue Pro R vs the FLIR Vue Pro. The radiometric version also can have emissivity values be entered which is necessary for precise data collection. The radiometric version is ideal for those in the inspection industry where taking accurate temperature data is a must.

9hz vs 30hz

What’s the difference between 9Hz and 30Hz refresh rate? The refresh rate refers to frequency at which the image on the screen is refreshed. The higher the refresh rate the less blur in the image. 9Hz means that the thermal image is updated 9 times every second compared to the 30 Hz which is updated 30 times a second. The 9Hz is great for most inspection uses as thermal images are gathered which are then analyzed to check for faults or abnormalities. For search and rescue (SAR) having the 30Hz is ideal since you are scanning for movement. In addition to having a better chance at finding someone, rescue teams generally record video the entire time and then re-watch the video to see if there is anything that they missed.

What is emissivity for infrared imaging? Emissivity is the efficiency at which an object gives off its thermal energy. Emissivity is affected by the surface type, humidity, atmospheric temperature, and wind. These factors should be recorded when taking measurements. Objects that have high emissivity include people, animals, concrete, trees, and rocks. Objects that have low emissivity include shiny metals such as aluminum foil and polished silver.

What are Isotherms? Isotherms highlight pre-set temperature ranges so when a specific temperature is detected it stands out, typically shown in an orange color. On the DJI Zenmuse XT2 there are pre-set isotherms, one for person search and one for fire. From our research, we found that many public safety officials advise against using isotherms during search and rescue since there are too many variables to take into consideration such as skin temperature, clothing emissivity, and environmental conditions. Public safety officials recommend using the black hot and white-hot color pallets to search for people.

How do environmental conditions impact infrared imaging? / What is the best time to use a thermal drone? The amount of thermal energy in a scene has a direct impact on the infrared image. Typically, the amount of infrared energy is attributed to the diurnal cycle, solar loading, and thermal crossover. The diurnal cycle is the daily heating and cooling of the Earth’s surface from the sun. Solar loading is when a scene absorbs more radiation from the sun’s rays the temperature differences between objects decrease. When two different objects in a scene are indistinguishable this is known as thermal crossover. With these factors in mind, early morning or late-night conditions are ideal.

Can infrared see through glass? Thermal drone cameras typically use medium and long wave infrared radiation which cannot pass through glass and typically reflect infrared radiation. For this reason, lenses of thermal cameras are generally made from Germanium which infrared radiation can easily pass through.

What color palette is the best to use for thermal imaging? White hot and black hot are by far the most popular for search and rescue. The object in the scene giving off the most radiation will be white and the object giving off the least will be black or vice versa. Everything in between will be a different shade of gray. White hot and black hot are the pallets recommended for search and rescue since the pallet highlights the objects in the scene with the greatest temperature difference. Fusion and Ironbow are ideal for roofs, solar panels, and outdoor electrical equipment. Lava and arctic color palettes enhance contrasting colors next to each other. These palette works the best when there is a high contrast between objects.

What drones are the best for thermal inspection? What drones are the best for commercial inspection? (Updated for 2020) A great entry level drone into the world for aerial infrared imaging is a DJI Mavic 2 Enterprise Dual. The Mavic 2 Enterprise Dual has a dual camera system featuring a 4k optical camera a lower resolution thermal sensor. Another added benefit of the Mavic Enterprise platform are the modular accessories (speakers, spotlight, beacon). It is important to note that the FLIR thermal sensor in the Mavic 2 Enterprise is pretty low resolution meaning that flying low to get accurate temperature data is a must.  

A step up would be the Matrice 200 with a DJI Zenmuse XT or XT2. The benefit of the XT2 is that it has a 4K regular camera and an infrared sensor in one which makes inspection or search and rescue much easier. The next step up would be the Matrice 210 with a DJI Zenmuse XT2 and a Zenmuse Z30. The Matrice 210 can carry two camera payloads. With the Zenmuse Z30 it gives operators the power of 30X optical zoom which means closer inspections at a distance. 

DJI Matrice 210 with zenmuse z30 and zenmuse xt2
DJI Matrice 210 with Zenmuse Z30 and Zenmuse XT2
Matrice 300 RTK Back and Front View with H20T

Matrice 300 RTK Back and Front View

New for 2020 we have the DJI Matrice 300 RTK. The DJI Matrice 300 has a 9.3 mile transmission range, 55 min flight time, 6 directional sensing, and IP45 water and dust protection. The Matrice 300 RTK is a durable drone ready for harsh environments and has the reliability and durability you  need when on the job. What makes the M300 an even better drone is the camera payload that can come with it. That camera would be the DJI Zenmuse H20T. The H20T has 4 sensors in one camera housing. There is a laser range finder, wide angle, zoom, and thermal camera. 

What is the best thermal drone camera? The best thermal drone camera will be dependent on the use case. If you are looking to do inspections or search for people, the DJI Zenmuse XT2 has the necessary configurations to meet the desired use case. The DJI Zenmuse XT2 is compatible with the DJI Matrice 200, 210 (RTK), and 600 Pro. If the job requires infrared gas imaging, then a cooled thermal core is necessary. The Workswell GIS 320 thermal camera is a great option due to its compact size. However, the GIS 320 requires its own gimbal and must be custom integrated onto the drone that it is going on.

As of now there is a close tie between the DJI Zenmuse XT2 and Zenmuse H20T. While the XT2 offers a variety of lens options, resolutions, and refresh rates the H20T has more sensors build in (laser range finder, wide angle, and zoom cameras. The H20T comes only in one configuration that being, 

Can you see gases with a thermal camera? This concept is commonly referred to as Optical Gas Imaging (OGI) and employs spectral filtering and various sensor optimizations such as cooling the thermal sensor to detect the absorptive and emissive properties of various gas compounds. In the resulting image, escaping gases look like smoke against a contrasting background. Video can be viewed in real time and can be recorded in the camera for tracking, archiving, and reporting. Once again, the Workswell GIS 320 thermal camera is a great option due to its compact size.

How are thermal/infrared drones used for Firefighting? Fire departments have been using handheld thermal imaging cameras for some time now. With thermal drones, crews can get a live stream of structure fires, wildfires, and forest fires from above as they can see through smoke. For wild and forest fires being able to see through smoke to identify the edge of the fire is crucial when planning the attack, not to mention identifying smoldering hot spots that can flare up. For structure fires thermal drones can provide valuable information about roof integrity. Giving ground crews valuable information about burn through rates and fire flow paths. For more information on how fire departments are using infrared drones see our 2017 infographic on firefighting drones.

How can drones be used for roof inspections? Remote aerial sensing technology gives inspection personnel more thorough, frequent, safer, and efficient inspections. Drones equipped with infrared cameras can be used to detect irregularities in insulation and pooling water. With a zoom camera drone, inspectors can visually identify problems without having to be physically there. This means greater efficiency for the inspector while providing better data to the client.durability


Single sensor cameras – Infrared sensor only: FLIR VUE PRO R, FLUR VUE PRO, DJI Zenmuse XT, DJI Zenmuse XT (R)

Dual sensor cameras – Standard RGB camera and Infrared camera: FLIR DUO, FLIR DUO R, FLIR DUO PRO RDJI Zenmuse XT2 R

Another large infrared camera manufacturer is Workswell. Workswell currently produces 3 thermal camera models for the UAV market.

Is the Inspire 2 compatible/work with the DJI Zenmuse XT or XT2? The Inspire 2 is not compatible with the DJI Zenmuse XT or DJI Zenmuse XT2. We here at Dronefly offer a solution to this problem. The FLIR Touch upgrade kit is a self-powered gimbal specifically designed to carry the FLIR Vue Pro. This add on gimbal gives the Inspire 2 the ability to capture thermal data while being able to carry either the DJI Zenmuse X4S or DJI Zenmuse X5S cameras.
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