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Surveillance fever: how does thermal technology check your temperature?

May 5, 2020  By Colin Bodbyl

The rapid spread of COVID-19 has created overwhelming demand for everything from surgical masks to toilet paper; even video surveillance has been caught up in the surge.

Thermal surveillance cameras with temperature monitoring are traditionally used for measuring the temperature of critical infrastructure. With COVID-19 however, measuring human body temperature has suddenly become its most popular use case. Video analytics are also playing a role in fighting COVID-19 by monitoring social distancing, an application that was previously unheard of.

With fever being a key symptom of COVID-19, health-care workers and regular citizens alike went in search of the easiest and fasted way to test people’s temperatures without coming into contact with them. There are two popular methods for doing this, thermal cameras and infrared thermometers. The science behind both products is the same. Thermal is most simply described as a region of the infrared light spectrum which is not visible to the human eye. So, while one product uses the term thermal and the other uses infrared, they are both measuring the same spectrum of light or waves emitted by heat.

Thermal cameras use a sensor array to capture infrared. Similar to a traditional camera’s image sensor, the array has a pixel dimension which is used to capture thousands of reference points in a scene and display them as an image. Not all thermal cameras can produce temperature measurements. Accurately measuring temperatures requires a radiometrically calibrated camera. For more precise measurements, some cameras also use a black box as a temperature reference point. A black box is a separately powered device that is placed in the camera’s view and maintains a consistent temperature which the camera can then use to compare against other temperatures in the scene. Different cameras have different ranges of accuracy and not all cameras are accurate enough to determine if a person has a fever or not.


The alternative to a thermal camera is an infrared thermometer. As mentioned, an infrared thermometer also measures light waves created by heat. Where an infrared thermometer differs from a thermal camera is that it uses a different sensor called a thermopile that converts the infrared light into heat which then creates an electrical signal that is ultimately measured to determine a temperature reading. Infrared thermometers have similar accuracy ranges to thermal cameras, but only measure a single point where the device is aimed, whereas thermal cameras can measure a larger area and are in turn less likely to miss something.

Another technology that has seen an increase in interest due to COVID-19 is video analytics or AI typically used to detect intruders. Video analytics are capable of distinguishing between people, vehicles and many other objects. Using the same technology, analytics providers are also able to determine distance between people as well as the total number of people in an area, two key measures in reducing the spread of COVID-19. While the implementation of this might seem challenging, one company, Voxel51, has applied the technology to live public video feeds from around the world. They are also publishing the data openly so others can see if people are following social distancing measures and how that behaviour correlates to the spread of the virus.

Technology like thermal imaging has already played a key role in reducing the spread, while video analytics is collecting data that is key to understanding the adherence to and effectiveness of social distancing measures.

We do not know how long COVID-19 will impact our lives or when life will go back to normal, but video surveillance has an important role to play, as always, in keeping people safe, only this time it is not from criminals but rather a dangerous virus.

Colin Bodbyl is the chief technology officer of Stealth Monitoring (www.stealthmonitoring.com).

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