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Stanhill, G., Division of Agricultural Meteorology, Volcani Institute of Agricultural Research, P. O. B. 6, Rehovot, Israel
Fuchs, M., Division of Agricultural Meteorology, Volcani Institute of Agricultural Research, P. O. B. 6, Rehovot, Israel
Oguntoyinbo, J., Division of Agricultural Meteorology, Volcani Institute of Agricultural Research, P. O. B. 6, Rehovot, Israel
The absolute errors to be expected in reflectivity measured with four different types of commercially available 2nd Class pyranometers have been enumerated and evaluated from laboratory studies and W. M. O. recommendations. The maximum errors to be expected were between ±10 and ±20% at a solar elevation of 60° and between ±20 and ±30% for a solar elevation of 10°. The comparative error, i. e., the difference in reflectivity measured by different types of pyranometers, was measured under field conditions and reached 25% at a solar elevation of 60° and 40% at 10°. Random errors, including those due to individual differences in pyranometers of the same type, were found to be negligibly small. Large and asymetrial diurnal variations in reflectivity were observed. They paralleled the diurnal changes in the fraction of diffuse incident radiation, but could not be explained by changes of the fractional infrared composition of solar radiation as the latter were very small. Analysis by multiple regression suggested that the reflectivity for the direct beam radiation was higher than for the diffuse radiation. © 1971 Springer-Verlag.
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The accuracy of field measurements of solar reflectivity
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Stanhill, G., Division of Agricultural Meteorology, Volcani Institute of Agricultural Research, P. O. B. 6, Rehovot, Israel
Fuchs, M., Division of Agricultural Meteorology, Volcani Institute of Agricultural Research, P. O. B. 6, Rehovot, Israel
Oguntoyinbo, J., Division of Agricultural Meteorology, Volcani Institute of Agricultural Research, P. O. B. 6, Rehovot, Israel
The accuracy of field measurements of solar reflectivity
The absolute errors to be expected in reflectivity measured with four different types of commercially available 2nd Class pyranometers have been enumerated and evaluated from laboratory studies and W. M. O. recommendations. The maximum errors to be expected were between ±10 and ±20% at a solar elevation of 60° and between ±20 and ±30% for a solar elevation of 10°. The comparative error, i. e., the difference in reflectivity measured by different types of pyranometers, was measured under field conditions and reached 25% at a solar elevation of 60° and 40% at 10°. Random errors, including those due to individual differences in pyranometers of the same type, were found to be negligibly small. Large and asymetrial diurnal variations in reflectivity were observed. They paralleled the diurnal changes in the fraction of diffuse incident radiation, but could not be explained by changes of the fractional infrared composition of solar radiation as the latter were very small. Analysis by multiple regression suggested that the reflectivity for the direct beam radiation was higher than for the diffuse radiation. © 1971 Springer-Verlag.
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