VISUAL RESOLUTION AND OPTICAL SCINTILLATION OVER SNOW, ICE, AND FROZEN GROUND. PART 1

• Main Authors: Portman,Donald J, Ryznar,Edward, elder,Floyd C, Noble,Vincent E
• Format: Report
• Language: English
• Subjects: ATMOSPHERES; BRIGHTNESS; ICE; LIGHT TRANSMISSION; MICROMETEOROLOGY; OPTICAL PROPERTIES; OPTICS; OSCILLATION; PERMAFROST; PHOTOMETERS; RESOLUTION; SNOW; VISION

Optical scintillation, visual resolution, and wind and temperature profiles were measured over snow, ice, and frozen ground. The data were analyzed to determine relationships between (1) scintillation and visual resolution and (2) scintillation and meteorological and surface conditions. The experimental results included (1) estimates of the limit of visual resolution, (2) telephotometer measurements of the apparent fluctuations in brightness (scintillation) of an artificial light source, and (3) measurements of wind direction and of the vertical distributions of wind speed and temperature. The optical path was 543 m long and 1.5 m above uniform horizontal surfaces. All scintillation and meteorological data are given in an appendix. The principal results of the analysis showed that for turbulent flow in stable stratification over snow (1) visual resolution deteriorted systematically as scintillation increased in intensity and (2) scintillation intensity increased with increase in vertical temperature gradient. Scintillation was at a minimun in the absence of thermal stratification and at a maximum (in very stable thermal stratification) during the sudden transition from laminar to turbulent flow. For a given temperature gradient, scintillation increased with increase in wind speed. When wind and temperature gradients were combined in terms of the Richardson number and related to scintillation, the data obtained over snow indicated a critical Richardson number of about 0.35. (Author)