Test of minimum resolvable temperature difference (MRTD) for thermal imaging system

Test of minimum resolvable temperature difference: A standard four-bar target is used in conjunction with a differential blackbody that can establish one blackbody isothermal temperature for the set of bars and another blackbody isothermal temperature for the set of conjugate bars, which are formed by the regions between the bars (Fig. 1).

The target is imaged onto the monochrome video monitor of a thermal imaging system where the image is viewed by an observer. The temperature difference between the bars and their conjugates, initially zero, is increased incrementally only until the observer can distinguish the four bars. This critical temperature difference is the MRTD.

The spatial distribution of temperature of each target must be measured remotely at the critical temperature difference that determines the MRTD. The mean temperature of each bar must not differ from that of any other bar by more than the measured MRTD. The background temperature and the spatial frequency of each target must be specified together with the measured value of MRTD.

The test importance lies in the fact that it relates to a thermal imaging system’s effectiveness for discerning details in a scene. MRTD values provide estimates of resolution capability and may be used to compare one system with another. Lower MRTD values indicate better resolution.