Study Of Improving The Uncertainty Of The Scattering Visibility Meter

Visibility is an important meteorological element, having a major impact on the maritime, aviation as well as land transport. Because large-scale chain accidents often have occurred and casualties and property losses have been caused by poor visibility, Visibility is also increasingly concerned by people. Forward scattering visibility meter become an important tool for measuring visibility because of its low cost, small size, easy installation and maintenance features. But the forward scattering visibility meter currently used on the market still appears greater uncertainty within a certain visibility, studying how to improve the uncertainty of forward scattering visibility meter is significant.The forward scattering visibility meter uses the lens to limit the receiver’s field angle generally and the receiving light beam is a cone of larger opening angle, so the measured angle has kind of uncertainty and this does not comply with the strict definition of angle scattering coefficient. Combinations of lenses and step-index fiber to limit the receiver’s field angle was proposed in this paper and this makes receiving light beam comply with the strict definition of angular scattering coefficient. The receiving light beam without spatial filter, which is large cone angle, is measured too. The angular scattering coefficient was measured by two ways to limit the field angle of the receiver. The ratio of the scattering coefficient is equal to the ratio of the scattering light signal by derivation of the formulas.The circuit of the measuring system is composed by light source modulation circuit, photodetection circuit, band-pass filter circuit, lock-in amplifier circuit and post-amplifier circuit. All kinds of noise in electronic circuit is fully considered in the circuit design. Multiple suppression methods were used to reduce the influence of noise in electronic circuit. Data collection, the average median filtering and data display were done by MSP430F149.The aerosol generator, TDA-4B, was used to generate six different concentrations of submicron-scale aerosol in experiment. Aerosol filled into customized containers and angle scattering coefficient of two methods was measured in these six kinds of concentration of aerosol particles. The measured angle scattering coefficient with lens is1.96times the angle scattering coefficient with combination of lens and fiber, which complies with scattering theory. The larger field angle of receiver causes lower visibility measurement values by calculation...