The Characteristics of the Eppley Pyrheliometer

Spectrophotometry of Radiation from Sun and Sky

“…(6) Effect of Changes in the Reflection Factor It can be shown that the intensity of radiation at the slit is proportional to l l-p (l-b) where p is the reflection factor of the sphere surface, and b is a constant depending on the dimensions of the sphere and annular opening. The factor (I-b) is a correction term to allow for the loss through the annular opening of some of the radiation reflected within the sphere.…”

“…The brightness of a portion of the sky may be expressed as a function of its zenith angle 6, azimuth r/>, and the time t. If we assume the brightness does not vary with azimuth (which is justified if the receiver is symmetrical), then for any given instant it can be shown that the energy per unit area per unit time from the whole sky, falling on a horizontal surface, is given by (6). cos6d6 (1) where t 1(6) takes into account variations in the brightness of the sky with zenith angle.…”

“…The second bracket in (6) corresponds to an element of area of width dx, such as KN in Fig. 6, and the second bracket in (7) .…”