Dependence on the distance to the object - Page 1
Forum section: electronics / general

author: rgbdt
author_rank: Newbie
timestamp: September 09, 2021, 01:52:29 pm
content: We purchased Seek Thermal C3 for the task of determining the skin temperature of people by their faces.https://www.thermal.com/oem.htmlWe also hope to measure people's core temperatures, but we are aware of the problems that go along with that.The main problem we encountered was a decrease in temperature readings as the thermal camera moved farther away from the person. You can see the results on the graph.Now we are trying to predict the distance to an object using neural networks and correct the temperature using the predicted distance.Is this a problem common to all thermal imaging cameras or is it only a problem with this model? Are there ways to deal with it?We don't use the black body for correction.

author: rgbdt
author_rank: Newbie
timestamp: September 09, 2021, 01:57:55 pm
content: It would also be great if you could recommend articles that describe how major thermal imaging manufacturers such as Seek and FLIR solve similar problems.

author: agiorgitis
author_rank: Regular Contributor
timestamp: September 09, 2021, 02:17:51 pm
content: Distance is not only the distance from the object, but also the air in between. Which means your prediction should also use air temperature and air density to make corrections.You can do some testing on different hours per day (with different air temperatures) and feed your neural network with those.It's also important that your senson has stabilized, temperature wise, before taking readings.

author: geggi1
author_rank: Frequent Contributor
timestamp: September 09, 2021, 02:51:02 pm
content: Its probably related to the resolution of the camera.A thermal camera sensor is basically working the same way as a regular photo sensor (CCD)When you get some distance less pixels with heat information will be available.The factor for dubbeling the distance is 1:4 so if you go form 1m to 2m the pixels covering the face will only be a quarter.You might be able to mitigate this a bit by implementing som kinde of distance measurement in your software.

author: Fraser
author_rank: Super Contributor
timestamp: September 09, 2021, 03:36:58 pm
content: This is just physics at work and normal behaviour in thermography, which is why thermal cameras use Distance to target, Ambient Temperature and Humidity in their measurement corrections. Many manufacturers do not publish their measurement correction algorithms. You could try askingFLIRSEEK for help regarding their correction algorithms. It may help if you tell them why you need such technical information and that it is for a worthy cause.This paper may be of interest to you as well…..https://www.spiedigitallibrary.org/journals/optical-engineering/volume-53/issue-07/074101/Handy-method-to-estimate-uncertainty-of-temperature-measurement-by-infrared/10.1117/1.OE.53.7.074101.fullNot wanting to be mean, but the C3 would not be my choice of thermal imaging camera for measuring human skin temperature. Ituses the LEPTON core and this wasnot really intended for accurate temperature measurements, especially as you are not using an ‘in scene’ temperature reference of known accuracy.

author: Fraser
author_rank: Super Contributor
timestamp: September 09, 2021, 03:47:49 pm
content: This paper may also be of interest. It relates to the thermographic study of the environment and the real world effects of distance etc on measurements within the scene. It may contain some useful real world data for your to work with, rather than just theoretical calculations.https://agritrop.cirad.fr/584611/1/Faye_et_al._2015-Journal_of_Thermal_Biology.pdfFraser

author: Fraser
author_rank: Super Contributor
timestamp: September 09, 2021, 03:49:56 pm
content: A FLIR document on measurement uncertainty in their cameras.https://www.flir.co.uk/discover/rd-science/infrared-camera-accuracy-and-uncertainty-in-plain-language/Fraser

author: Fraser
author_rank: Super Contributor
timestamp: September 09, 2021, 03:51:44 pm
content: And another paper that may be of interest to you…..https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.852.2058&rep=rep1&type=pdfFraser

author: bap2703
author_rank: Regular Contributor
timestamp: September 09, 2021, 07:11:42 pm
content: A simple answer : the atmosphere absorbs more or less light depending on the wavelength.LWIR, around 8-12 µm is a window of transitivity : in that band, gases absorb less.But they still do!So as you put more gas between your source and your camera, you get less and less signal.Now different sensors and systems are more or less sensitive to that.Want to build a device that will be mainly used to look at PCBs not even a meter away? Then design your system for a large wavelength range : you'll get more light at close range, but it will decrease with range.Want to build a device mainly used to see miles away : you'd better build your system so that you get a constant amount of light regardless of the distance. That means filtering out more wavelength, meaning your device is less sensitive. So you'll probably need to compensate by having a more sensitive sensor in the first place.When you have the luxury to do so, just replace or remove the atmosphere

author: svgurus
author_rank: Regular Contributor
timestamp: September 09, 2021, 07:16:02 pm
content: Quote from: Fraser on September 09, 2021, 03:36:58 pmLooks like you thought about Flir c3, but here some product from seek is used, link provided above doesnt describe it. And one can never be too mean about seek's products, in my very humble opinion) but the point is right, usually good 320-384 core is used for this quite responcible task. Once i saw Testo 890(vga, crazy price, etc) standing in Moscow metro station entrance, inside watchman's glass cubicle but i dont think it used there not for crown scanning) rgbdt, do you live in Moscow?) What company do you work for? maybe i can borrow you some stuff

author: Fraser
author_rank: Super Contributor
timestamp: September 09, 2021, 07:43:42 pm
content: The SEEK Scan product uses a temperature reference in the scene and custom software to produce acceptable accuracy of measurement. Without the in-scene temperature reference it is incapable of the accuracy required for fever detection in humansThis is one reason why the Chinese microbolometer manufacturers developed their own miniature cores as they tried using SEEK consumer grade cores for fever screening and let’s just say they found the accuracy lacking.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 09, 2021, 09:14:59 pm
content: Does the C3 not have a distance to target setting for internal correction? My E60's got one and I believe I've seen it in FLIR's software, though this would not correct for a variety of target distances in a single shot (or you couldn't reset the range between varied target distances).

author: svgurus
author_rank: Regular Contributor
timestamp: September 09, 2021, 11:17:30 pm
content: I found, he means Seek Mosaic core c3 series 4mm qvga, 56*42 degrees fov.

author: Fraser
author_rank: Super Contributor
timestamp: September 09, 2021, 11:34:45 pm
content: Darn it, I read C3 and immediately thought of the FLIR C3My mistake. I have corrected my previous post but the comments remain. I own the SEEK OEM core and have it’s SDK. I would not want to use that core for fever detection without an in-scene thermal reference but rgbdt intends to operate in a person to person differential mode so maybe they can achieve what they need from this basic cores performance.Fraser