Different stages of the target search process correspond to different detection levels. Detection level is a visual ability evaluation method that combines system performance with human vision. It needs to be completed through visual psychological experiments. Foreign countries have done a lot in this regard, and Johnson linked the target detection problem with the equivalent strip pattern detection problem based on experiments. It is possible to use the target equivalent strip pattern resolvability to determine the ability of the imaging system to recognize the target without considering the nature of the target and image defects. Figures 2-15 describe the concept of this equivalent stripe pattern.

 

The equivalent strip pattern of the target is a set of strip-shaped patterns with equal black and white intervals, the total height of which is the critical dimension of the target that can be basically recognized, that is, the minimum projected size of the target, and the strip length is perpendicular to the direction of the critical dimension. inches across the target. The equivalent stripe pattern resolvability is the number of resolvable stripes contained in the target critical dimension, usually expressed as "cycles/critical dimension". Johnson demonstrated that equivalent strip pattern resolvability can be used to predict target detection and recognition. He experimented with eight military vehicles and a standing man. The detection criteria for various targets are determined. This criterion is often referred to as the Johnson criterion.

 

Because the number of strip periods N required for the above-mentioned various detection levels is obtained under the probability of 50%. Therefore, for the corresponding strip period number N under other probabilities. The relationship between the test and the number of equivalent bands contained in the target.