Influence of transmissometers’ light source spectral distribution in measuring visibility

Abstract

Presently, the difference in the spectral distribution of light sources is not been sufficiently taken into account when measuring and calibrating the transmissometers. As such, the visibility measurement result cannot be to be traced to the World Meteorological Organization (WMO) definition of meteorological optical range (MOR). In this study, a method is proposed to trace the spectral distribution of transmissometers’ light sources to the 2700 K incandescent light’s spectral distribution in MOR definition. Then a traceability basis of the light source’s spectral distribution is proposed, and a model is established to determine the influence of the light source’s absolute color temperature on the MOR measurement accuracy. At the transmissometers’ typical baseline lengths of 10, 20, 30, 50, and 75 m, the absolute color temperature range and their corresponding spectral simulation error range equivalent to 2700 K incandescent lamp are obtained. Finally, the Monte Carlo method is used to simulate and analyze the MOR error corresponding to the absolute color temperature of different spectral simulation errors at five typical baseline lengths. The results show that in 10 m–600 m of MOR, the maximum simulated MOR absolute error is 42 m, which is less than 50 m, in 600 m–1500 m of MOR, the maximum simulated MOR relative error is 2.9%, which is much lower than 10% and in 1500 m–10 km of MOR, the maximum simulated MOR relative error is 18.6%, which is less than 20%, the MOR measurement accuracy is improved to the International Civil Aviation Organisation (ICAO)’s recommended requirements, thus confirming the accuracy of our theoretical research. We expect that this work will help establish the standard procedure for the SI-traceable calibration of transmissometers.