带通滤波器对能见度测量不确定度的影响

Effect of band-pass filter on uncertainty of visibility measurement

在能见度测量中,为了抑制环境光变化对测量不确定度的影响,在光发射端对探测光束进行调制,在接收端对探测到的光电信号进行带通滤波。带通滤波器的特性参数受到工作环境温度变化的影响,导致频响函数变化,从而引入能见度测量的不确定度。以二阶有源带通滤波器为例,从传输函数入手分析了带通滤波器频响幅度随温度变化的规律,实验测定了频响幅度随温度变化的关系。结果表明：在高能见度天气状况下,在15℃~40℃温度范围内,环境温度每变化1℃,带通滤波器将贡献约4.5%的不确定度;低能见度时,带通滤波器的影响比高能见度时小得多。

In the visibility meter, in order to suppress the impact of uncertainty of measurement by the ambient light changes, the probe beam in optical transmitter was modulated, and the band-pass filter was used in photoelectric signal receiver. Since the frequency response function could change, which was induced by the band-pass filter characteristic parameters changing with the temperature in the working environment, the uncertainty was introduced in the measurement of visibility. Taking a second order active band-pass filter as an example, the band pass filter frequency response amplitude variation with temperature was analyzed from the transfer function, and the the frequency response amplitude variation with temperature was measured by experiment. The results show that the band-pass filter provides about 4.5% uncertainty with the environment temperature changing per 1℃, at 15℃ -40℃ in high visibility weather conditions, and the effect of band-pass filter on the measurement of visibility is much smaller in low visibility conditions.