Measurements of infrared and visible extinction in adverse weather

Document Type

Article

Publication Date

12-30-1981

Abstract

As part of a program to develop improved models for infrared and visible extinction in adverse weather, a one-kilometer transmission range has been established near Houghton, Michigan, where annual rainfall is about twenty inches, fog is common, and annual snowfall often exceeds 200 inches. A Barnes Engineering Transmissometer is used to record transmission in the 3-5 and 8-14 micrometer bands, and a Helium-Neon laser transmissometer is used to record transmission at 0.63 micrometers. During transmission measurements, an automated weather station periodically records standard weather parameters. Results are presented as plots of the logarithm of the infrared extinction coefficient versus the logarithm of the visible extinction coefficient (the GAP model format). Extinction coefficients for rain tend to be along straight lines, in fairly good agreement with the GAP model, when the atmosphere contains rain drops but not suspended droplets. Measured extinction coefficients in snow tend to lie along straight lines on the log-log plots, with slight differences from one snow storm to another, which are attributed to differences in the types of snowflakes. Measurements in fog, recorded at one minute intervals, trace the evolution of fogs as they form, mature, and dissipate. These processes tend to follow straight lines on the log-log plots, in contrast to the widely scattered data recorded at larger time intervals in other measurement programs, and this suggests that a better model for fog extinction can be developed by considering the evolution of the fog drop size distribution. © 1981, SPIE.

Publication Title

Proceedings of SPIE - The International Society for Optical Engineering

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