On the Measurement of Atmospheric Extinction of Solar Radiation and the Sun's Aureole
1961 Volume 12 Issue 1 Pages 57-74
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1961 Volume 12 Issue 1 Pages 57-74
A new type of spectrophotometer is designed for the measurement of the angular distribution of sky radiation in a monochromatic range and also for that of spectral distribution of direct solar radiation. The principal parts of the instrument a the telescop e, a double monochrometer and a multiplier phototube.
The opening angle of the telescope is about 54 ' and a special precaution is taken for removing stray light in the instrument and so the measurement of skylight as near as one degree from the sun is possible.
Using this instrument we meas u red the spectral intensities of direct sunlight and those of the sun's aureole as far as 10 degrees with an interval of one degree for various altitudes of the sun. On the basis of the results of observation the spectral distribution of atmospheric extinction coefficient and the angular distribution of sky radiation were considered.
As regards thespectral distribution of extinction coefficient observed curves showed two regions of different tendencies, namely a steep rising toward the shorter wave-length in the blue and ultra-violet region and a comparatively flat tendency in the yellow and red region. The anomalous transmission in the near ultra-violet which was discussed by DEIRMENDJIANa nd SEKERA (1956) could not be found according to this observation.
One of the observed characteristics of the angular distribution of sky radiation is the tendency in the ultra-violet region at a very low sun elevation, where the sign of the gradient is reversed as compared with the other wave-lengths. This tendency was explained by calculation as the effect of multiple scattering.
As to the effect of dust particl e s, a preliminary analysis was done using the results of calculations of DEIRMENDJIAN (1957) and those of BULLRICH (1952) concerning, respectively, the measurement of extinction coefficients and that of aureole. Marked deviation from the inverse fourth power law seems to exist concerning the size distribution of dust particles as far as the preliminary results are concerned.
