Thermal Detection Range
Detection, recognition and identification distances for a thermal camera and lens.
Thermal camera
Detector pitch from the datasheet, commonly 12 or 17 µm
Target
Results
Fix the highlighted values to see results.
Ranges
Horizontal FOV
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IFOV
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Range = critical dimension × focal length ÷ (pixels on target × pixel pitch). Johnson criteria as used for staring arrays: Detect 1.5 px, Recognize 6 px, Identify 12 px across the critical dimension, for a 50% probability with good thermal contrast and clear air.
Questions
What are the Johnson criteria?
A rule for how many pixels must cover a target's critical dimension: 1.5 to detect it, 6 to recognize what it is and 12 to identify it, each at a 50% probability.
What critical dimension is used for a person and a vehicle?
0.75 m for a person and 2.3 m for a vehicle.
Why do two cameras with the same resolution have different ranges?
Range scales with focal length and inversely with pixel pitch. A 12 µm detector with the same lens reaches about 40% farther than a 17 µm one.
Does weather change the range?
Yes. These ranges assume good thermal contrast and clear air. Fog, rain and a small temperature difference between target and background shorten them.