Research Of Digital Photogrammetric Method For Nighttime Visibility Measurement Based On Dual Light Sources

Atmospheric visibility, which used to characterize atmospheric transparency, plays an important role in weather forecast, environmental monitoring, transportation, power supply, communications engineering, industry and agriculture, military and so on. Restricted from illumination and human factors, nighttime visibility is more difficult to measure than daytime visibility. Therefore, it is important to investigate a method to measure nigthttime visibility with higher precision and easier implementation.Aiming at the uncertainty in measures of nighttime visibility, a system based on digital photography had been presented in this paper. Departing from the foundational theory of measureing visibility, the calculation model of nighttime visibility by means of double light sources was introduced.After the analysis and calculation to performance index,such as dynamic range, the digit of ADC and field depth,we made a reasonable selection for technical parameters of digital camera. For reducing the uncertainty caused by background light noise, an improved method which can limit CCD field angle by using shading cylinder was proposed, and the formula of visibility was inferred by Allard Laws.The geometrical dimensions and parameters of shading cylinder were optimized in the contrast test which used to detect the system performance. The test with different observation bases was to analyze the gray information of light and the visibilities on three conditions:in dark background, without shading cylinder in light background, with shading cylinder in light background.Further more, we developed a graphics-oriented user interface based on GUI which could obtaine visibility in according with image.Experiment result shows that the correlation coefficient and average relative errors are0.3564and22.07%when compared with visibility in dark background and without shading cylinder, the correlation coefficient and average relative errors are0.927and5.73%when compared with visibility in dark background and with shading cylinder.It can be seen that, the ability of restraining interference from background noise is enhanced after the improvement, thus can get more accurate results with measuring nighttime visibility. This paper also offers reference for design of similar systems.