Pyrheliometric measurements with special regard to the circumsolar sky radiation

Abstract

In the present article the influence of aperture and atmospheric turbidity on the readings of pyrheliometers, used within the meteorological network, has been considered on the basis of measurements and observations concerning the radiation intensity within the solar aureole now available. We have emphasized the fact that the constants of secondary pyrheliometers, as these constants generally are determined, are dependent on apertures of involved instruments and on the atmospheric turbidity at the occasion when the standardization is made, and also that secondary instruments generally, if the derived constants are applied to the readings, must show differences from one another which are dependent upon turbidity and aperture conditions. As the effect of these factors is of systematic character, they must be seriously considered if an accuracy surpassing about ± 1.5 per cent shall be reached. Observations made in connection with the International Comparisons of Pyrheliometers at Davos 1964 are found to confirm the ideas expressed here and in previous notes by the present authors. Applications are suggested as regards (1) the difference found to exist between the old pyrheliometric standard scales, as regards (2) the future organization of Intenational Pyrheliometer Comparisons and (3) concerning the desirability of standardizing, to a greater extent than has been made up to now, the aperture conditions of pyrheliometers within the meteorological network.