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Proceedings Paper

Long-path transmissometer for measuring ambient atmospheric extinction
Author(s): John Victor Molenar; Gerald C. Persha; William C. Malm
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Paper Abstract

With the passage of the 1977 Clean Air Act Amendments, the United States Congress emphasized visibility protection for the pristine areas of the country as a major national goal. Federal programs were implemented to estimate existing levels of atmospheric extinction. Until recently, this has been accomplished primarily by the use of various techniques to measure apparent target/horizon sky contrast. While the ability of these methods to accurately determine contrast is well proven, the estimation of extinction using the Koschmieder relationship is usually compromised by theoretical assumptions that are typically not met in practice. To address this problem, the United States National Park Service has supported the development, testing, and deployment of an instrument that accurately and reliably measures the transmission of an ambient atmospheric optical path. The average atmospheric extinction coefficient of the path can be calculated directly from this measurement. This transmissometer consists of a constant output light source transmitter and a computer-controlled photometer receiver. The irradiance at visible wavelengths from the transmitter can be measured to a high degree of accuracy both day and night over path lengths of 0.5 to 30km. A complete description of the transmissometer will be presented. Atmospheric optical considerations will be combined with design parameters and experimental data to confirm the ability of this instrument to make an accurate, precise, and reliable extinction measurement.

Paper Details

Date Published: 1 August 1990
PDF: 19 pages
Proc. SPIE 1269, Environment and Pollution Measurement Sensors and Systems, (1 August 1990); doi: 10.1117/12.20342
Show Author Affiliations
John Victor Molenar, Air Resource Specialists, Inc. (United States)
Gerald C. Persha, Optec, Inc. (United States)
William C. Malm, National Park Service (United States)

Published in SPIE Proceedings Vol. 1269:
Environment and Pollution Measurement Sensors and Systems
Hans Ole Nielsen, Editor(s)

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