Abstract

A new instrument for the measurement of atmospheric extinction coefficient—the Point Visibility Meter (PVM)—is introduced and its principle of operation discussed. The instrument measures the amount of light scattered at a particular forward scattering angle by haze or fog; the extinction coefficient σ is then found from the empirical law relating σ to the scatter at this angle. Detailed calculations of aerosol scattering properties using Mie theory are given to support this empirical law. Error estimates based on these calculations indicate rms errors of less than ±12% for a range of σ values 2–60 km⁻¹. Field trials of the instrument against standard transmissometers confirm these theoretical findings and show a linearity of instrumental output with extinction coefficient, with an rms error of ±11.7%.

© 1975 Optical Society of America

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