Preliminary study on visual recognition under low visibility conditions caused by artificial dynamic smog

Abstract

Aim: To quantitatively evaluate the effect of a simulated smog environment on human visual function by psychophysical methods.

Methods: The smog environment was simulated in a 40×40×60 cm³ glass chamber filled with a PM2.5 aerosol, and 14 subjects with normal visual function were examined by psychophysical methods with the foggy smog box placed in front of their eyes. The transmission of light through the smog box, an indication of the percentage concentration of smog, was determined with a luminance meter. Visual function under different smog concentrations was evaluated by the E-visual acuity, crowded E-visual acuity and contrast sensitivity.

Results: E-visual acuity, crowded E-visual acuity and contrast sensitivity were all impaired with a decrease in the transmission rate (TR) according to power functions, with invariable exponents of -1.41, -1.62 and -0.7, respectively, and R² values of 0.99 for E and crowded E-visual acuity, 0.96 for contrast sensitivity. Crowded E-visual acuity decreased faster than E-visual acuity. There was a good correlation between the TR, extinction coefficient and visibility under heavy-smog conditions.

Conclusion: Increases in smog concentration have a strong effect on visual function.

Keywords: artificial smog; low visibility conditions; visual recognition.

Figure 1. Gamma correction of the CRT monitor with a luminance meter.

Figure 2. The Gamma correction principle

A: The corresponding point between the input brightness value and the actual brightness value of the screen; B: The fitting curve of corresponding points; C: The compensation curve generated by the correction program; D: The corrected program input brightness value and screen actual brightness value.

Figure 3. The smog dissipation process curve

The dissipation process is not perfectly homogeneous, but it is slow and relatively smooth.

Figure 4. Relationship between transmission rate and visual target contrast

As the smog concentration deceased, the rate of light transmission increased, and the visual target contrast increased.

Figure 5. The E-visual acuity model (A) and the crowded E-visual acuity model (B)

As the transmission rate increases, both E-visual acuity and crowded E-visual acuity were improved as a power function of the rate of light transmission.

Figure 6. The contrast sensitivity model

With the increase in the smog percentage concentration, the rate of light transmission and contrast sensitivity was decreased following a power function.

Figure 7. The relationship between TR, β and visibility

As the smog concentration decreases and the light TR increases, the value of β decreases quickly. Correspondingly, the visibility increases. At a TR of 10%, at which the decrease in E-visual acuity and crowded E-visual acuity begins to accelerate, the visibility is only approximately 2-3 m. It belongs to grade IV severe in Haze Level for Observation and Prediction.