OBSERVATION OF NON-RAYLEIGH SCATTERING IN THE SPECTRUM OF THE DAY SKY IN THE REGION 0.56 TO 2.2 MICRONS

Abstract

Spectral records of the day skylight from 0.56 to 2.2µ were obtained at 5415- and 2200-ft stations for the morning sun along the solar almucantar with a lead-sulfide cell and glass-prism spectrometer. Scattering intensities in the spectral region 1.0 to 2.2µ appear unusually large up to 30 deg from the sun. Comparison of the recorded scattered intensity with direct solar radiation shows the trend from the high infrared scatter toward Rayleigh scattering. A similar result is obtained by examining the records of Adel. Examination of the scattering function for selected wavelengths shows the loss of visibie light in the forward direction and predominance of infrared. Comparison with Hulburt's curve for the total visible region shows similarity only from 90 to 180 deg from the sun. The slope of the scattering function at small angles for different wavelengths is used as an approximate method for obtaining particle size. Values of roughly 0.5µ for the visible region and 3.5µ for the infrared region have been estimated. The latter figure appears unusually large.