Abstract
Abstract. A digital optical method "DOM-Vis" was developed to measure atmospheric visibility. In this method, two digital pictures were taken of the same target at two different distances along the same straight line. The pictures were analyzed to determine the optical contrasts between the target and its sky background and, subsequently, visibility is calculated. A light transfer scheme for DOM-Vis was delineated, based upon which algorithms were developed for both daytime and nighttime scenarios. A series of field tests were carried out under different weather and meteorological conditions to study the impacts of such operational parameters as exposure, optical zoom, distance between the two camera locations, and distance of the target. This method was validated by comparing the DOM-Vis results with those measured using a co-located Vaisala® visibility meter. The visibility under which this study was carried out ranged from 1 to 20 km. This digital-photography-based method possesses a number of advantages compared with traditional methods. Pre-calibration of the detector with a visibility meter is not required. In addition, the application of DOM-Vis is independent of several factors like the exact distance of the target and several camera setting parameters. These features make DOM-Vis more adaptive under a variety of field conditions.
Highlights
Introduction tions for the same targetMidSdloetloind(1E95a2r)tthested 1000 people to find that the threshold contrast varies from 0.01 to 0.20.Atmospheric visibility can be described by the maximum horizontal distance at which a target with a sky background can be visually observed by human eyes (Horvath, 1981)
It is interpreted as “visual range” (Malm, 1979), which is determined with different definitions of threshold contrast
The pixel values corresponding to the sky background in the far and near pictures should be 2t3he same
Summary
The radiances of the light received by the near camera, after transferring through the atmosphere along path X1, are Nb1 (from the dark target) and Nw1 (from the sky background). Into Eq (6), T2 can be calculated from the ratios of the (1) radiances from the target and its sky background received by. The radiances of the light received by the far camera, after transferring through the atmosphere along path X2, are Nb2 (from the dark target) and Nw2 (from the sky background), respectively.
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