Improve atmospheric visibility accuracy with the divergence angle correction of the probe beam

The probe beam is the important part of the visibility meter. And the divergence angle size of the probe beam affects the accuracy of visibility. In the paper, the relation between the divergence angle and the visibility relative error was established by the experiment model. The aerosol generator produced different concentration atmosphere, which was measured as atmospheric sample under the different visibility. The relationship between the divergence angle of the probe beam and the different atmospheric samples was established. The detection values and correction function were obtained at different divergence angles under various atmospheric samples. The experimental result shows that the divergence angle of the probe beam affects the visibility measurement. And the larger the divergence angle is, the greater the measurement error is. The measurement of the divergence angle must be corrected. Using the measurement method with the divergence angle correction, under the low visibility conditions, the relative error of the visibility is reduced from 25% to 10% at least, in the divergence angle range of 25mrad. When the allowable error is 5%, the allowable value of the divergence angle is increased by one time.