Quantification of atmospheric visibility with dual digital cameras during daytime and nighttime

摘要

A digital optical method "DOM-Vis" was developed to measure atmosphericvisibility. In this method, two digital pictures were taken of the sametarget at two different distances along the same straight line. The pictureswere analyzed to determine the optical contrasts between the target and itssky background and, subsequently, visibility is calculated. A light transferscheme for DOM-Vis was delineated, based upon which algorithms weredeveloped for both daytime and nighttime scenarios. A series of field testswere carried out under different weather and meteorological conditions tostudy the impacts of such operational parameters as exposure, optical zoom,distance between the two camera locations, and distance of the target. Thismethod was validated by comparing the DOM-Vis results with those measuredusing a co-located Vaisala visibility meter. The visibilityunder which this study was carried out ranged from 1 to 20 km. Thisdigital-photography-based method possesses a number of advantages comparedwith traditional methods. Pre-calibration of the detector with a visibilitymeter is not required. In addition, the application of DOM-Vis isindependent of several factors like the exact distance of the target andseveral camera setting parameters. These features make DOM-Vis more adaptiveunder a variety of field conditions.