Detecting Coronavirus Fevers With Thermal Cameras

By: Ethan Ace, John Honovich, and Charles Rollet, Published on Feb 03, 2020

Thermal cameras have emerged as a widely used tool for authorities to help detect fevers in the response to Wuhan coronavirus.

But there are significant concerns about how accurately they work. In this report, we examine:

  • Biggest accuracy issues
  • Setup examples
  • Problems examples
  • Temperature variance issues
  • Optimizing accuracy
  • Survey of options ranging from FLIR and Optotherm from the US to various China suppliers including Dahua, Hikvision and Sunell
  • Performance claims and pricing differentials for thermal products offered.
  • The rising importance

Biggest Accuracy Issues

In our research of various options, we found 3 fundamental accuracy issues:

  • Camera temperature detection accuracy - while some manufacturers claim accuracy to as precise as 0.3°C, we are skeptical of actual field accuracy as these are likely overinflated. Surveillance users can compare to lux ratings.
  • The positioning of cameras - many cameras being used to detect temperature are positioned perpendicularly to the person and/or the person is on the move. This significantly reduces the probability of an accurate reading, as one is briefly getting the side of a person's head, which typically has a lower temperature reading.
  • Reading temperature on the forehead and other areas of the face is heavily impacted by environmental factors. In airports, for example, subjects entering from outside will be skewed by hot, sunny days or very cold temperatures, or those running to catch a flight may be flushed, raising surface skin temperature.

Pricing variance: Beyond accuracy issues, the other major issue that stood out was drastic differences in pricing, ranging from the ~$10,000 range for US cameras like FLIR and Optotherm that are marketed specifically for human body temperature reading to hundreds of dollars for China models. However, FLIR does offer much less expensive cameras that detect temperature but do not recommend because of accuracy limitations. We have not tested any of the FLIR or China low-cost models but would be quite skeptical of their accuracy.

Key Issue: No Independent Tests

A core issue is there are no independent tests of thermal camera performance/accuracy and no independent standards to measure against. This has allowed manufacturers to tout products meant for body/fire detection as a fever solution, or falsely claim pinpoint accuracy at long distances. We urge caution against buying low-cost thermal solutions from any manufacturer.

Setup Examples

First is an example from Wuhan, the center of the epidemic, where a NY Times reporter took a photo of herself having her temperature detected. We have translated the screen for context:

Despite translating and searching in both English and Chinese, we could not find the name of the manufacturer. The on-screen text indicates it the device combines color and thermal cameras, color for display purposes and thermal for measuring temperature.

In some cases, people are moving directly towards the camera, as this AFP photo shows FLIR in Malaysia:

Here is another case where the person is moving directly but notice how the person head often will turn the other way, as this AFP news video of the airport in Hanoi, Vietnam using OptoTherm equipment can be seen:

In the case below, the camera (highlighted in the red box) is at a moderate angle to traffic, as shown in this NY Times report showing a Thailand mall:

The crowd of people makes it more difficult to tell. Note; the red indicator for temperatures of 38.0° C (equivalent to 100.4° C).

By contrast, other detectors are used to measure temperature person by person as this example in the Philippines shows:

Of course, the obvious tradeoff of this vs thermal cameras is that a person is required to measure temperatures one at a time, which requires a lot more time and staff to implement.

Problems Examples

A common problem is that readings come in too low, especially when the camera is reading the side of someone's head:

And again in the example below:

There is also a recent example of a handheld infrared thermometer having significant accuracy issues, as shown by this Economist reporter who tweeted that one gave him a 32.1ºC / 89.8ºF temperature, which would mean he is dying of hypothermia:

Neither the model nor make of that device nor other particulars were available. The underlying point of under readings, though, remains clear.

UPDATE: another example of infrared thermometers' unreliability comes from an NYT reporter, who tweeted he was constantly getting "corpse-level" 34ºC readings:

Skin Temperature Lower Than Body Temperature

Likely contributing to these issues is that skin temperature is colder than someone's actual (internal) body temperature. Known as the "skin temperature offset" as explained by OptoTherm, this difference can be a few degrees Celsius:

Optimizing Accuracy

To get the most accurate readings, according to a source in this field, one needs:

the person face the camera, remove glasses and allow the camera to image the inner canthus [corner] of the eye

Glasses can distort the readings since they interfere with measuring heat from the body. Moreover, the inner canthus of the eye emits higher, more accurate temperature than the skin.

Moreover, like with cameras generally, the pixel density has a factor with lower pixel density increasing accuracy issues:

Trying to get a reading of a person far away will also significantly decrease performance as recommendations are to get 9 to 16 pixels on the 1/4 inch area of the eye, which effectively limits the overall camera's FoV

One technique that is sometimes used is effectively doing relative measurements, such that what stands out is a person whose readings are higher than others in the immediate vicinity / time frame. This still has the risk of people with fevers being missed if the camera only reads the side of their head at a poor angle or distance, etc.

Accuracy

FLIR states that thermal cameras typically have accuracy +/- 2ºC, but that "with proper calibration and attention to factors such as ambient temperature, emissivity, and spot size, the possible margin of error can be less than 1ºC."

If deployed properly - with a focus on individual people rather than large groups all at once - thermal cameras are useful, but will not catch all those infected, said Ben Cowling, a professor at the University of Hong Kong's School of Public Health. This is chiefly since some infected people may not have a fever yet.

Yes quite a number of the imported cases have been picked up by thermal scanners. It can pick up people with a high body temperature. Those can then be verified with a hand-held thermometer. It does not pick up people who have been infected but do not yet show symptoms ("during the incubation period"). For the new coronavirus, the incubation period could be up to 14 days. So it will catch some infected people but miss others. It does not pick up infected people with symptoms but who do not have a fever, for example the Chinese tourist who went to France, departed with a fever but took paracetamol to evade the thermal scanners. Some infected people may have symptoms (e.g. coughing) but no fever. It is useful but will not identify every infected person.

Limited Studies

A 2010 study from the US' Center for Disease Control that a FLIR A20M camera and an Optotherm Thermoscreen were each "reasonably accurate in detecting fever and were better predictors of fever than self report". IPVM could not find a more recent study as authoritative.

However, worth noting the test was limited to the much more expensive units and is a decade old.

FLIR Offerings

While FLIR has various thermal cameras, FLIR only markets a limited number of thermal cameras for body temperature detection. Notably, FLIR does not recommend its conventional security thermal cameras for body temperature detection.

FLIR provided us a list of models they say may be considered include the portable FLIR E75, E85, E95, T530, T540, T840, T860 and the FLIR T1020 (T1K), or fixed mount A310, A315, A615, and A655sc, the latter of which is a more accurate, higher resolution, but more expensive option.

US FDA 510K Certification

In the US, there is a Food and Drug Administration (FDA) certification called 510(K) which impacts the use of thermal for detecting body temperatures, according to both FLIR and Optotherm.

FLIR says:

These FDA-certified cameras (510(k) submission K033967) were designated with an intended use specifically in public areas, i.e., airports, to allow operators to visualize and document temperature patterns and changes.

Here is the FDA 501(K) listing for FLIR and the 2004 summary PDF report.

We do not understand enough how the 501(K) process works or how it actually verifies performance since it requires comparison to devices released prior to 1976:

Submitters must compare their device to one or more similar legally marketed devices and make and support their substantial equivalence claims. A legally marketed device is a device that was legally marketed prior to May 28, 1976

OptoTherm Offering

OptoTherm sells a single solution called Thermoscreen. This clip from the AFP news video shows it in action:

Notably, OptoTherm declares on their website that it cannot be sold in the US due to a current lack of 510(K) certification:

This product is currently for export only. Optotherm is currently undergoing the US FDA Premarket Notification (510k) submission process for medical devices. As soon as Thermoscreen has been cleared, this product will be available for purchase in the US.

PRC Manufacturer Dubious Claims

IPVM has noticed several PRC manufacturers touting their thermal solutions in light of the Wuhan virus. However all of them had significant issues:

  • A Sunell thermal camera demo showing pinpoint accuracy at a long distance, which is suspicious to impossible
  • Dahua claiming its thermal cameras can detect fevers with pinpoint accuracy, even though they are meant for detecting fires in electrical substations and bodies at border crossings
  • Hikvision deleting a tweet showing a wide range of body temperature detections for a single person

Panda Cam Claim from Sunell

A Sunell employee on LinkedIn posted that their "Panda" camera could help "protect us from Coronary virus" [sic]. This is the Sunell TN-5 we saw at ISC West last year.

However, this solution is unproven and makes a number of dubious claims, including pinpoint (to a fraction of a degree) temperature readings for people at a significant distance, as shown in this demo:

At such a high distance, with little to no focus on the crucial inner part of the eye, such a specific body temperature reading is simply not possible.

Even more astounding, this demo gets 4 readings in a row all within a fraction of 1 degree Celsius from ideal body temperature, which means this is astoundingly lucky, incredibly accurate or simply rigged:

Additionally, in its specs, Sunell states the Panda cam has +/- "less than 0.3°C" accuracy in ideal conditions, which is far more accurate than the typical +/- 1°C accuracy in ideal conditions that FLIR says is possible. Their specs also don't include a recommended minimum distance or a description of what ideal conditions actually are.

There is no evidence the Panda camera is being deployed against the coronavirus. When IPVM reached out to Sunell, they were unable to answer any questions about the SN-T5.

Hikvision Deletes Thermal Tweet, Sends Equipment to Wuhan

Shortly after the virus became international news, Hikvision Italy's Twitter account shared a video of thermal camera surveillance footage referencing current events, implying that Hikvision products could be used as a coronavirus solution. Below is the video, which shows a considerable range of temperature:

However, when we reached out to Hikvision, they deleted the video and told us:

We have deleted the tweet, it was part of an ongoing thermal campaign in Italy and could now be deemed misplaced.

Separately, a local news report from Hikvision's Hangzhou HQ said that on January 22, Hikvision dispatched nearly 1,000 "sets of video capturing and analytics products as well as thermal detection devices" to Wuhan's Hospital Number 7, sending another 40 sets of thermal devices a day later due to local shortages:

海康威视红外测温产品驰援武汉协助当地防控疫情

The specific Hikvision devices being packaged are the H10 infrared thermometers, which are sold on Alibaba for about $288 (1999 CNY) and also have reported accuracy of +/- 2ºC. This is the same accuracy as FLIR, a company which specializes in thermal solutions, and we have no way of confirming whether this reported accuracy is true. These devices are also only advertised for industrial purposes.

Another news report states Hikvision has set up an emergency committee to deal with the virus response.

Hikvision declined to comment on its response to the Wuhan virus.

Dahua Touts Unrelated Thermal Product Line

In response to the virus, Dahua's Chinese social media account issued a post titled "Dahua will always guard you!" that touted its thermal camera and access control solutions, claiming accuracy within 0.3ºC like Sunell.

However, 3 of the products above have different purposes than human body temperature, according to Dahua's own promotional video.

The two bullet cams (BF5x00 left, BF2120 right) are meant for indoor monitoring/perimeter protection/fire detection while the camera on the lower right (PT8x20b) is meant for city surveillance (i.e. body detection) and detecting fire hazards at electrical substations. We could not identify the fourth camera. Furthermore, while Dahua's post touted +/- 0.3°C accuracy, these cameras' specs all list +/- 2°C accuracy.

Fire and body detection, obviously, requires much lower accuracy than detecting a human fever, but there is no mention of these cameras' original purpose in Dahua's post. The promotion of this series amid the coronavirus crisis showcases the danger in taking surveillance manufacturers' claims at face value.

PRC Government Mandates Anti-Virus Equipment Production

China is currently experiencing critical shortages of thermal detection equipment, face masks, hand sanitizer, etc, leading the PRC government to announce measures ensuring the production of such goods:

Although this directive mandates enterprises to "strengthen product quality management", IPVM has not found any mention here (or anywhere else) of specific measures targeting thermal screening accuracy.

Delivery Food Includes Temperature of Those Involved

The measuring of temperatures is becoming a broad phenomenon inside of China. For example, this Twitter user shared an image of a delivery slip where the "food preparer, packer, and the courier all have to measure their temperatures":

The card above is from Yunhaiyao, a chain restaurant serving Yunnan cuisine across major cities in China and overseas. We saw other reports on Weibo of similar activities from other chains.

Outlook - Thermal Challenges But Difficult Conditions

While using thermal cameras for temperature detection presents challenges, the difficult conditions faced clearly have spurred their use. And the quick acceleration of these challenges means that most users and few suppliers are ready with highly accurate thermal detectors.

We plan to update this report as we have more information on accuracy, best practices, options and usage of thermal cameras detecting body temperatures and alerting on fevers.

Comments (13)

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worth noting that PRC state media just tweeted out a video of a drone taking people's temperatures:

Given the difficulty of getting ideal conditions & close ups of people's inner eyes using this method, this is highly unlikely to be accurate (although it does look cool).

Wow, the degree to which they are throwing everything they have (including some very dubious tools) at this outbreak really highlights how spooked the PRC is...

I think if they really were spooked they wouldn't be using "Benny Hill" type music in the video.

Charles, very interesting. Btw, here is a screencap showing the drone's user interface and that the person has a 35.6° C (96.1° F) reading:

Given how low these readings tend to be, if someone actually gets a 'normal' 37° C / 98.6° F reading, is that considered a fever.

Also, going outdoors in winter will lower someone's surface skin temperature.

FWIW more recent research indicates that the "normal" body temp is actually lower than 98.6 these days.

When is body temperature too low? - Harvard Health

I'm curious to know if any solutions described above (FLIR, OptoTherm, HIk/Dahua) use reference based temperatures for increased accuracy? This seems like an easy way to combat emissivity and would seem prudent during this outbreak.

Soon everyone will be wearing mud and clay to avoid detection....

Currently we are doing the tests using the Camera that's on this photo and the Blackbody device, and you are right, the only correct logics to get most accurate results is to use reference and comparison method, rather than relying just on the measurement results.

The fourth unidentified camera in the Dahua image above is the blackbody device. Having been in contact with the Dahua country team, the thermal camera alone is claimed to have +/- 1 degree celsius. With the addition of the blackbody device, the accuracy is improved to +/- 0.3 degree celsius

As I know a blackbody can be also impacted by ambient environment.

I wonder whether it is possible to get the ±0.3℃ accuracy if the blackbody is not correct.

I added this example into the post - an NYT reporter tweeted that he was constantly getting "corpse level" body temp readings from infrared thermometers, noting they often "simply don't function":

Separately, Chinese state media outlet People's Daily (the same outlet behind the drone video) tweeted about thermal cameras deployed against the coronavirus detecting people's farts. Not very mature or useful, but that doesn't seem to be the point...

UPDATE: the video shared by People's Daily is 100% fake, Gizmodo explains.

Dahua has a new social media post / video showing one of its camera being used in its hometown of Hangzhou:

SCMP has a video on Twitter showing a thermal camera in operation, screencap below:

Interestingly, again, the temperature detected is so slow, 28 / 32.5° C.

I do wonder how you can screen so many people at the same time with such an inaccurate process.

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