ATTENUATION OF A PARALLEL BEAM OF LIGHT, PARTICULARLY BY SNOW,
Abstract
A pulsed light has been used in a conventional optical system with a nearly-parallel beam of light: divergence less than 0.1 degrees. Attenuation measurements over a 123 m path were made in Montreal in the early months of 1964. Attenuation by falling snow appeared to be proportional to the rate of snowfall, and is obviously proportional to distance. The value found was approximately 18(db 1/ km)/(mmw 1/hr), using mmw to denote the millimetres of water to which the snow would melt. This value dropped from 18 to 10 for wet snow and snow pellets. Attenuation by rain was only 0.25(db 1/km)/(mm 1/hr). Observed visual range in snow varied inversely as the rate of snowfall, and was 1 km when the rate was 1 mmw 1/hr. Fluctuations noted in the received signal could be related to thermal eddies near the transmitter, and these are considered, along with laser possibilities, in an appendix. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1965
- Accession Number
- AD0615383
Entities
People
- Olav Lillesaeter
Organizations
- McGill University