Two independent methods were used: direct spectrophotometry through the transparent windows of the atmospheric gases, and measurement of the number and diameter of the water droplets, followed by a Mie-theory calculation of the spectral transmittance. Results from the two methods are in good agreement when the media are sufficiently homogeneous, as for a quiet haze or fog and artificial smoke.
The following kinds of atmospheres were considered: hazes (optical density per km in the visible spectrum is less than 2); a small number of small-drop fogs (optical density per km less than 10); evolving fogs (which have changing distributions of drop-diameters); nonevolving, slightly selective fogs; artificial smokes. In addition, some information is given on the statistical distribution of drop-diameters.
It was found that the transmission of haze increased markedly with increasing wavelength, from the visible to 10 microns, but this marked increase was not found for fogs.
© 1957 Optical Society of AmericaFull Article | PDF Article
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