Atmospheric turbidity, global illumination and planetary albedo of the earth

On the basis of measurements by A. J. Drummond of the natural illumination from sun and sky in South Africa, a formula has been derived, expressing the global illumination at sea level as a function of air mass and turbidity. From this formula the present author has derived the relative decrease in illumination caused by the intervention of the atmosphere, or what is here termed the “photometric loss factor”. The dependence of this factor on turbidity and air mass is studied. From its value at various latitudes the planetary photometric albedo of the system earth + cloudfree atmosphere is derived. If the planetary photometric albedo (atmosphere partly cloudy) of Danjon is accepted, we derive a value for the planetary energy albedo of the earth of 0.333. It is suggested that this value is slightly too low. With application of here-derived albedo values for the clear atmosphere and accepting Houghton’s value 0.56 for the cloud albedo we obtain a planetary energy albedo of the earth of 0.380. This value implies that the photometric albedo ought to be found slightly higher than the value derived by Danjon from measurements of the brightness of the moon, namely 0.43 instead of 0.39.