How far that thermal camera can see?

 

To understand how far a thermal camera (or infrared camera) can see, firstly you need to know how big size the object you want to see is.

Besides, what is the standard of "seeing" you define exactly?

Generally speaking, the "seeing" would divide into several levels:

1. Theoretical maximum distance: as long as there is one pixel on the thermal imaging screen to reflect the object, but in this case there will no accurate temperature measurement

2. Theoretical temperature measurement distance: when the targeted object to be able to measure the accurate temperature, it generally needs at least 3 pixels of detector are reflected on the device, so the theoretical temperature measurement distance is the amount that the object can cast 3 pixels on thermal imaging camera.

3. Only observation, no temperature measurement, but identifiable, then this requires a method called the Johnson Criterion.

This criterion including:

(1) fuzzy outlines are visible

(2) shapes are recognizable

(3) details are recognizable

Maximum imaging distance = number of vertical pixels × target size (in meters) × 1000

Vertical field of view × 17.45

or

Number of horizontal pixels × target size (in meters) × 1000

Horizontal field of view × 17.45