Research of Measuring High Visibility at Night Based on Dual Light Sources Digital Image

Research on measuring night visibility using digital images mainly focused on low visibility conditions nowadays. Also, the long term observation leads to fluctuations of the single light source, which would undermine the measuring range and precision. In this context, this paper presents the dual light sources measurement method to eliminate the fluctuations of single source and to achieve both high measuring range and precision at night conditions. The source of visibility measuring error is firstly formulated through an error analysis. Then we propose a dual light sources framework that yields two identical beams to measure the visibility, which is advantageous over the single light source method and capable of measuring high visibility. In the experiments, the stability of the dual light sources is firstly tested by a 72-hour running. The average luminance ration of dual light sources is 0.9932 and the average relative error is 0.04%. The relative error of dual light sources luminance ration is only 0.2% when the fluctuations of single source is as high as 2.28%. Then the dual light sources is applied in the digital image night visibility measuring system to evaluate its validity. The result shows that the dual light sources method is capable of measuring the range of 390 times of baseline (40m baseline) with the error less than 15%, which fully meets the meteorological demands.