Visual Resolution and Optical Scintillation in Stable Stratification over Snow

Abstract

The effects of turbulent fluctuations of atmospheric density are seen as rapid changes in the brightness of a distant light source (scintillation) and in the position and size of distant objects (shimmer). The results of an investigation of the effects in a horizontal optical path 543 m long and 1.5 m high over a uniform snow surface are described. It was found that deterioration in visual resolution caused by shimmer was most pronounced when the atmosphere was clear, a time when the detection and recognition of distant objects were otherwise unimpeded. Visual resolution deteriorated and scintillation intensity increased systematically with increasing inversion magnitude in turbulent flow. Resolution was best in windy and cloudy conditions and poorest on clear nights with light wind speeds.