Thermal Cameras and Distance
When people shop around for a thermal imaging device, one of the most frequent questions they ask is “how far can I see with it?” It may sound strange, but this question is extremely complex and many-sided. To get a precise answer one needs to take into account a variety of factors that could be separated into two groups: inner and outer.
Before we identify these factors, let us first define the terms “Detection”, “Recognition” and “Identification”. These definitions are based on work by J. Johnson who introduced a criteria to assess performance of optical equipment back in 1950s.
Detection: you can distinguish an unknown object from the background.
Recognition: you can tell what kind of object this is (e.g. human, car, etc.)
Identification: you can describe the object in details (e.g. a male civilian or a four-door sedan).
Under this criteria for a human – you need just 1.5 pixels to detect a target, 6 to Recognize it and 12 to ID it – so you can see that it really depends how the manufacture defines a detection to give you the amazing detection ranges.
Hence believing you are going to ‘see’ a deer at 2,000m is best described as BS – Remember Thermals only have 2-4x optical zoom!!
Below is a image of a Canadian Geese to give you a idea – and there is a lot more pixels in this image than the minimum and its more realistic
Internal factors that determine the range are related to the characteristics of the thermal system you are using. These parameters are: detector sensitivity, lens focal length, lens f-number, thermal detector’s resolution, display resolution and type (small or large), brightness and focus
External factors involve object size, environmental and weather conditions, the difference between the object and what the background is
Even your own experience counts
It now becomes quite obvious that one cannot give a definitive and universal answer to that “how far?” question. Some manufacturers bluntly state detection, recognition and identification figures, or DRI for short, without even mentioning what these performance figures depend on.
You’ve probably seen the nice looking deer, Bear! or Giraffe photos from competitors marketing – ever wondered how far they are?
REAL CLOSE is the answer
If they are not showing you the distances then you need to ask – some of the images are that close, that you are in a LOT of trouble
Have a look at this video – Its about UAV cameras, however the principal is the same