对比法测量气象能见度的理论分析

本文从能见度定义出发，提出了一种新型的能见度测量方法——对比法。对比测量法就是以自然水平天空为背景，人工设定一个亮度可调的目标物，用同一测量系统分别测量目标物亮度与天空背景亮度的差异，当该差值小于某设定阈值时，就认为该目标物的视亮度与天空背景亮度相同，根据目标物的实际亮度值就可以计算出大气透过率，进而计算气象能见度。采用检测目标物亮度与天空背景亮度对比确定气象光学距离方法的优点在于：理论上采用能见度定义，满足目标物刚好“可见”条件，实际使用中只需要人工目标物设计成亮度多级重复循环变化，对于接收端仅需要测量亮度差是否达到预先设定值进行判断。只要人工目标物有足够的亮度重复精度，就能保证测量结果的准确性，而检测器实质上是一个差分检测放大系统，这种差分电路对于共模信号都有较好的抑制能力，并且不需要测量绝对光强度，可以降低技术工艺方面要求。本文从理论推导人手，根据实际情况进行了必要的简化，得出对比法的计算公式，最后根据实际天空背景亮度变化情况给出了人工目标物亮度的变化范围。

ANTITHESIS-MEASURING ATMOSPHERIC TRANSMISSION COEFFICIENT OR METEOROLOGICAL VISIBILITY

In the paper,based on the defination of meteorological visibility, antithesis-- a new type of contract method of visibility measurement is brought up. Against natural horizontal sky,setting up an artifiCial object which brightness can be adjusted, the contrast of the artifieial object against sky is measured with a simple measurement which used an operational differential amplifier circuit. When the contrast at a distance is below a value of threshold of contrast,the brightness of sky background and the brightness at distance of the artical target is equal. The atmospheric transmission eoefficient and meteorological visibility are calculated based on the brightness at zero distance of the target.The advantage of antithesis lies on:the absolute illumination measurement is not needed,demand of technological design can be decreased greatly.In this paper,inference theory is done at first. Necessary simplification is carried out based on actual atmosphere condition. The calculattinn formulation of antithesis method is obtained. Lastly,according to the illumination of sky background,the brightness variation range of the artificial object is given.