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Visibility is one of the important parameters of meteorological observation. Based on the principle of infrared forward scattering and phase-locked amplification, a self-stable visibility meter is designed. The transmitter unit of visibility meter generates 875 nm light pulse at 2.3 kHz. Narrow pulse modulation technology is used to solve the problem of total power and instantaneous power of infrared LED when working, as well as the problem of natural heat dissipation, so as to reduce the aging speed of LED. The photodiode of the backscattering receiver monitors the transmitted light intensity, and adjusts the automatic feedback and the amplitude of the light pulse to keep the light intensity of the LED as the preset value. The visibility meter is compared with Visala PWD20 in the visibility measurement and verification laboratory. The experimental results show that the measurement deviations of one minute and ten minutes are within ±10% and ±4% in the range of 10~20000m. The forward scattering visibility meter is stable and has small measurement error, which can meet the requirements of visibility detection of meteorological stations.
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