Understanding Infrared Thermography Reading 3

■ Thermal Resolution
thermal resolution can be measured using a procedure developed for military
evaluation of night vision systems. This procedure uses standard resolution
targets as illustrated in Figure 4.11 and is described as follows:
1. Set up the test pattern such that ΔT exceeds the manufacturer's
specification for minimum resolvable temperature difference.
2. Determine the spatial frequency I t of the target in cycles per milli-radian as
follows:
a. the number of radians equals the bar width W divided by the distance d to
the target (example: 2 mm at 1 m = 2 mRad); and
b. the spatial frequency, I t = 1 cycle / (1 bar + 1 space) = 1 / (W + S).
(If W = 2 mRad and S = 2 mRad, then I t = 1/(2 + 2) = 0.25 cycles per
milli-radian).
Charlie Chong/ Fion Zhang