A Comparison of the Funk and Idso Techniques for Measuring Hemispherical All-Wave Radiation

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Abstract
A comparison of four Fritschen net radiometers and two Funk net radiometers converted to hemispherical operation by the procedures of Idso and Funk, respectively, was made in a large, open, bare field over a period of 17 consecutive days. Data were collected every half‐hour during this period. Under both clear and cloudy conditions, the mean 24 h energy totals received by each instrument type differed by only 2.3%. The Idso technique generally gave the higher results throughout the entire 24 h period, and agreed almost exactly with the combination of measured solar and calculated clear sky atmospheric thermal radiation utilizing the Idso‐Jackson formula. If the Swinbank formula had been used, however, the theoretical results would have been about 2% lower and thus closer to the Funk results. Since there is no basis for choosing between these two formulas in the air temperature range of this study, both instrument transformation techniques were concluded to be equally valid.

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