How far can an infrared thermal imager see?

Users often ask a question when purchasing an infrared thermal imaging camera: How far can an infrared thermal imaging camera see? This is a particularly important question, but one that is difficult to explain clearly. For example, our thermal imaging camera can see the sun 146×106 kilometers away, but it cannot be said that the detection distance of the thermal imaging camera can reach 146×106 kilometers. But the detection distance is another issue that must be made clear, because customers buy thermal imaging cameras to detect and monitor targets. Huawang Intelligent Technology Director told us a Johnson criterion, let us learn about it together and see how to determine the target detection distance.

Johnson criterion: Detection distance is the result of a combination of subjective and objective factors. Subjective factors are related to the observer’s visual psychology, experience and other factors. To answer "How far can a thermal imaging camera see", we must first clarify "what does seeing clearly" mean? For example, when detecting a target, A may think that he has seen it clearly, but B may think that he has not seen it clearly. Therefore, there must be an objective and unified evaluation standard. A lot of work has been done in this area abroad. Based on experiments, Johnson connected the target detection problem with equivalent stripe detection. Many studies have shown that it is possible to use the resolution of the target's equivalent stripes to determine the target recognition ability of an infrared thermal imaging camera imaging system without considering the nature of the target and image defects. This is the Johnson criterion.

Target detection can be divided into three levels: detection (discovery), recognition and identification.

A.Detection

Detection is defined as: finding a target within the field of view. At this time, the image formed by the target must occupy more than 1.5 pixels in the critical size direction.

B.Identification

Recognition is defined as: the target can be classified, that is, it can be identified as a tank, truck, or person. This means that the image formed by the target must occupy more than 6 pixels in the critical size direction.

C. Identify

The definition of identification is: the model and other characteristics of the target that can be distinguished, such as distinguishing between friend and foe. This means that the image formed by the target must occupy more than 12 pixels in the critical size direction.

The above are all data obtained under the condition that the probability is 50%, that is, the target can be found just right, and the contrast between the target and the background is 1. From the Johnson criterion above, we can see how far a set of infrared thermal imaging cameras can see , is determined by factors such as target size, lens focal length, detector performance, etc.

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