LABORATORY AND FIELD INVESTIGATIONS OF EPPLEY RADIATION SENSORS

Abstract

More precise radiation measurements in the Antarctic are required for studies designed to assess the radiation and heat budgets of that area. These requirements inspired the present investigation which is aimed at the experimental determination of certain of the instrumental characteristics and their consequences. Laboratory investigations of a group of Eppley pyranometers verifies previous findings that the temperature response is a unique characteristic of each instrument which can produce radiation-values 14 percent too high under the extreme Antarctic temperature conditions and differences between instruments at the same temperature of 3 to 8 percent. Tests made on the effect of inverting the pyranometer for the measurement of reflected solar radiation show that, the instrument sensitivity decreases by 4 to 6 percent in this position. A test on one normal incidence pyrheliometer indicates virtually no temperature effect. Weather Bureau calibrations of several pyrheliometers give results in excellent agreement with the calibrations performed by Eppley Laboratory. Field shade calibrations and simultaneous exposure comparisons of a group of Eppley pyranometers at the South Pole indicate that the computation of the total solar radiation should probably be made using separate direct and diffuse calibration factors for the pyranometers.