Question 5.5: Four solar radiometers are exposed side by side. A and B hav...
Four solar radiometers are exposed side by side. A and B have clear glass domes transmitting all wavelengths in the solar spectrum; C and D have domes that transmit 95% of the radiant energy from 700 to 3000 nm and no radiation below 700 nm. A and C receive global (total) radiation whereas B and D have a shade ring that intercepts 10% of radiation from the sky as well as all the direct solar beam. On a cloudless summer day the instruments give the following outputs: A 11.00 mV; B 1.30 mV; C 5.30 mV; and D 0.25 mV. Assuming that all instruments have the same sensitivity, 12.0 µV W^{-1} m^{-2}, calculate (i) the ratio of diffuse to global radiation, (ii) the fraction of photosynthetically active radiation (0.4–0.7 µm) in the diffuse component, (iii) the fraction of visible radiation in the direct solar beam, and (iv) the global irradiance in the photosynthetically active waveband.
Corrected irradiances are A = 916; B = 120; C = 465; D = 25 W m^{-2}. Then (i) 120/916 = 0.13; (ii) (120 − 25)/120 = 0.79; (iii) (916 − 465 − 120 + 25)/(916 − 120) = 356/796 = 0.45.