Field study of the performance of visibility sensors

In order to determine the best visibility sensor to be used in the climatological condition in Hong Kong, a field study of visibility sensors has been conducted at the meteorological garden of the Hong Kong International Airport (HKIA). The existing model of transmissometer, namely, Flamingo, is used as the basis in the study. A number of visibility sensors are involved, including a commonly used forward scatter sensor FD-12P, and the new generation of transmissometer LT31. The comparison has been made for four months and preliminary results would be presented in this paper. The sensor comparison is made by using box plot of the ratio of meteorological optical range (MOR) data from different sensors. It is noted that in convective rain in the summer, all sensors show similar behaviour in the measurement of MOR. However, in haze and mist, LT31 gives more consistent readings with Flamingo than FD-12P. It appears that the forward scatter sensor tends to over-read the MOR in lower visibility conditions in haze/mist. The correlation between MOR and the concentration of suspending particulates in the air would also be discussed.