Call number:
ZSP-202-111,1
In:
Research report / Cold Regions Research and Engineering Laboratory, 111,1
Description / Table of Contents:
Summary: 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 deteriorated systematically as scintillation increased in intensity and (2) scintilliation intensity increased with increase in vertical temperature gradient. Scintilliation was at a minimum 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, scintilliation increased with increase in wind speed. When wind and temperature gradients were combined in terms of the Richardson number and related to scintilliation, the data obtained over snow indicated a critical Richardson number of about 0.35. Scintilliation power spectra for eight periods revealed characteristics that could be related to visual resolution, the Richardson number and the mean wind speed component normal to the optical path. NOTE: This file is large. Allow your browser several minutes to download the file.
Type of Medium:
Series available for loan
Pages:
iii, 32, A17, B44 Seiten
,
Illustrationen
Series Statement:
Research report / Cold Regions Research and Engineering Laboratory 111,1
URL:
https://hdl.handle.net/11681/5837
Language:
English
Note:
CONTENTS
Preface
Page
Summary
Introduction
The problem
Previous work
Plan of the investigation
Conclusions
Visual resolution and scintillation
Visual resolution and wind, temperature, and surface conditions
Visual resolution and height and length of optical path
Results
Measurements
Analysis and discussion
Visual resolution and scintillation relationships
Scintillation and micrometeorological parameters
Index of refraction fluctuations
Scintillation and the temperature profile
Scintillation and average wind speed
Combined effects of wind speed and temperature gradient
Scintillation and surface roughness
Scintillation power spectra
Scintillation and path length
References
Appendix A: Equipment and procedures
Appendix B: Micrometeorological and scintillation data
Location:
AWI Archive
Branch Library:
AWI Library
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