Study Of Visibility Measurement Error Based On Laser-transmissometer

Visibility is known as the visibility distance, which is widely used in the field of Aviation and environmental monitoring. It's an important indicator used to measure atmospheric transparency.Visibility is one significant meteorological influence factor for Aviation. It has great impacts on air transport safety. When visibility is less than 1 km,it would affect the taking off and landing of aircraft,bring potential risk. In recent years, there is always rain, fog and haze weather with low visibility. The existing measurement apparatus working under the condition of these weather could be influenced by various factors, such as the complex aerosol type and multiple scattering phenomenon, which cause measuring error. The way to reduce the measurement error under low visibility has become a hot research topic in the field of aviation.Transmissometer has its own advantages, such as simple inversion algorithm, high precision measurement, becoming the powerful tool in the field of atmospheric detection, visibility measurement and aerosol distribution detection. The existing transmissometers still exist deficiencies when working in the peculiar environment of atmospheric aerosol in China. At present, white LED used as light source in most transmissometer equipment, although according with the definition of visibility and vision principle,it can't meet the requirements of the baseline length within a certain range of measurement error, and also can't meet the request of WMO for visibility measurement range. Laser source was thought to be used to improve transmissometer equipment. However, due to the influence of visibility detection environment,laser transmissometers still exist a certain measuring error. According to the requirement of aviation and optical parameters of actual transmissometers, the working model of a laser transmissometer has been set up. Considering both multiple scattering and laser aerosol transmission characteristics, the visibility measurement error has been analyzed and investigated. The results showed that:1. Different kinds of aerosols have different laser attenuation properties on same wavelength. And the same kind of aerosols also have different laser attenuation properties on different wavelength. Some complements of the measurement results of transmittance should be made to reduce the measurement error.2. Multiple scattering phenomenon is obvious under low visibility weather conditions, such as rain and fog. Due to the structure characteristics of laser transmissometers, multiple scattering effects on visibility measurement can be partly suppressed, but a certain deviation can exist between themeasurement results and the real value. Some complements of the measurement results of transmittance should be made to reduce the measurement error.