Reliability of the polar nephelometer for the measurement of visibility in fog.
The relation between the extinction coefficient of light at lambda = 0.55 microm and the scattered intensity was studied as a function of the scattering angle and the wavelength, in connection with its use in the measurement of visibility with the polar nephelometer. Computations used 239 spectra of natural fogs; they considered 181 scattering angles, 22 wavelengths from 0.25 to 5 microm, three cases of polarization, and four classes of visibility. Results show that for each wavelength within the interval micro = 0.25-1.06 microm and for each polarization and visibility class, there exists a corresponding well-defined angular interval in which the above relation is linear and quite reliable. The center and the width of the angular intervals, as well as the relative standard deviation concerning the relation at hand, depend strictly on the wavelength and the class of visibility considered; they range between 26 and 56 deg, 6 and 23 deg, and 0.5 and 3.5%, respectively, so that by a proper choice of avelength and related angular interval, visibility can be determined within 0.5%.
Tonna
G
G
Shifrin
K S
KS