Comparison Test And Analysis Of Multi-type Visibility Instruments In Different Environments

In this paper,the observation data of visibility,related meteorological elements,particle mass concentration and particle size obtained through the comparative observation tests of various types of visibility meters under different environments were used to explore the measured value errors and differences between the forward scattering visibility meters and transmission visibility meters,and lidar visibility meters under different meteorological conditions.The results in the above experiments were showed as follows:1.In the cabin,the deviation between the measured values of the transmission visibility meter and the forward scattering visibility meter was small and had good consistence.The average relative deviation of the measured values of the two visibility meters was 7.86%,and the average absolute deviation increased as the visibility increased.2.The changes of difference between the measured values of the forward scattering meter and transmission visibility meter in the field observation test base was slightly different from that in the case of pure water fog.Under different weather phenomena,the ratio of the measured value of the forward scattering meter to the transmission visibility meter(VIS_FS/VIS_T)changed significantly,and the overall trend increased with the increase in visibility.The difference between the observation values of the two types of visibility meters was the largest in rainy days,with an average relative deviation of 22.16%,and the difference between the two types of visibility meter observations in foggy days was the smallest,with an average relative deviation of 16.65%.Under the conditions of non-precipitation weathers,83%of the measured values from the forward scattering visibility meters were greater than those of the transmissive visibility meters at the same time.With the air quality changed from good to severely polluted,and the average absolute error between the two has been reduced from 655 m to 175 m.Under high humidity,the scattering coefficient of particulate matter was absolutely dominant in atmospheric extinction.The measured values of the two visibility meters were close.Under low humidity,the absorption coefficient of particulate matter cannot be ignored.The measured value of the forward scattering visibility meter was much greater than the measured value of the transmission visibility meter.3.The difference changes of the measured values between the lidar visibility meter and the forward scattering visibility meter in the field observation tests was shown as follows:under fog,haze and precipitation weather phenomena,the measured value of the forward scattering visibility meter was greater than the measured value of the lidar visibility meter in general when the visibility is low,and this situation accounted for 84.81%.With the increase in visibility,the average absolute deviation of the measured value of the lidar visibility meter and the measured value of the forward scattering visibility meter showed an increasing trend,while the average relative deviation showed a decreasing trend.During the pollution process,the superposition of multiple scattering signals increased the backscatter signal,and the measured value of the lidar visibility meter was lower than that of the forward scattering visibility meter.Under high humidity fog conditions,due to the combined effects of aerosol hygroscopicity growth and fog drop extinction,the measured values of the forward scattering visibility meter and the lidar visibility meter were relatively small and not much different.Under precipitation conditions,the backscattered energy increased,and the measured value of the lidar visibility meter was too small.The lidar visibility meter can intuitively discover the occurrence and dissipation of fog,which is suitable for the monitoring and early warning of fog.