Integrally and spectrally direct normal incidence radiation measurements and their bearing on atmospheric transmission on Baghdad

Abstract

The loss in the received amounts of normal incidence solar radiation at the ground level at noon time reaches 47% of that incident outside the earth’s atmosphere. The corresponding depletion figures in the amount of direct radiation received in the studied spectral band were 33% in the band less than 530 mμ, 50% in the visible range (530< λ<695 mμ) and 46% in the infrared range ( λ>695 mμ) of the solar spectrum. The fractions of the spectral bands to the normal incidence solar radiation at the ground level are in the yearly average 30%, 20% and 49% for the above mentioned spectral bands, respectively. The extinction coefficient for normal incidence solar radiation range was 0.36–0.60 with a mean value of 0.50. Approximately, a similar trend occurs for the energy in the visible and in the infrared ranges of the solar spectrum. Extinction below 530 mμ was found to vary over 0.23–0.41 with smaller values occurring during the warmer months.