Thermal Offset Correction Methods for Sensitivity of PSP Pyranometer
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摘要: PSP总日射表在我国一直作为标准总日射表和质量优良的辐射仪器在使用,2006年以前还曾作为国家散射标准,在太阳辐射量值传递中测量标准散射辐射,通过成分和法计算标准总日射辐照度。总日射表的校准在晴天条件下进行,此时天空无云,由于热偏移为负值,导致对短波灵敏度系数被低估。2011年10月14日—11月15日在北京密云上甸子大气本底站进行了对比观测试验,通过对不同总日射表热偏移订正方法的试验与研究,进行了5种热偏移订正方法的比较。通过订正,在用于室外成分和法校准时,PSP表的灵敏度系数的准确度可提高1%,进而提高总辐射的测量准确度。Abstract: The PSP pyranometer is used as a reference pyranometer and a reliable in strument in China. Before 2006 it is once used as national diffused reference to measure the reference diffused irradiance, the value of which is used in the sum composition method to calculate the reference global irradiance. The probability distribution of the nighttime thermal offsets within the pyranometers demonstrates near normal distribution. The offset of PSP type pyranometers is larger than that of 8-48 and CMP22 type. Finding the characteristics of the offset within different types of pyranometers and doing the calibration will improve the accuracy of diffused irradiance. The pyranometer calibration is done underclear sky. The negative thermal offset of the pyranometer causes that the sensitivity is underestimated. By the experiment and study on the thermal offset correction method for different type pyranometer, five correction methods are compared. The net longwave sensitivity method: Calculating the net longwave sensitivity of the pyranometer using longwave blackbody radiation, which is used in the sum composition method outdoors to correct the thermal offset of the pyranometer to reduce the offset effects. The differential algorithm with the reference global irradiance: Comparing it with the reference value derived from the sum composition method using the absolute cavity radiometer and CMP22 type secondary standard pyranometer with shading. The net longwave equation method: Analyzing the data of pyranometers and PIR type pyrgeometers measured at night to correct thermal offset. The cover method: Covering the dome of pyranometers in daytime to measure the offset of pyranometer directly. Using the voltage output of pyranometer in the nighttime as the thermal offset: Calculating the average voltage (night) when solar is 7° lower than horizon and transform it to irradiance as the thermal offset. When using the sum composition method to calibrate PSP pyranometer, the correction results of the net longwave sensitivity method is better than other methods. The result of the cover method is more close to the net longwave sensitivity method, the correction effects using the night voltage output method is not good. Drawing the daytime offset curves separately using the five offset correction methods, the net longwave equation method and the net longwave sensitivity method is more close to the reference value. But these methods are only confined to the shaded pyranometers, because shading makes pyranometer performs more like in the night. For unshading pyranometers, because of the effects of direct irradiance, the five correction methods are distinctly different with the true value. When using CMP22 and 8-48 pyranometers with shading in the sum composition method to test the reference diffused irradiance, the thermal offset could be ignored. But the CMP22 or 8-48 pyranometer should be calibrated by "shade/unshade" method to reduce the effects of offset for sensitivity.When the net longwave sensitivity method or the cover method is used in the sum composition method, the accuracy of PSP's sensitivity could be improved 1%.
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Key words:
- pyranometer;
- thermal offset;
- correction method
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表 1 各方法得到的总日射表热偏移误差比较 (单位:W·m-2)
Table 1 Thermal offset comparison of pyranometer from various methods (unit:W·m-2)
表号 型号 方法1 方法2 方法3 方法4 方法5 20462F3 PSP -7.4 -10.5 -4.8 -3.3 20463F3 PSP -7.8 -14.3 -4.3 -3.0 33734F3 PSP -5.4 -11.6 -6.7 -8.1 -2.7 33779 8-48 -1.4 3.3 -0.3 060016 CMP22 -0.2 -2.2 -1.2 100180 CMP22 -2.1 -1.0 -1.0 表 2 成分和法用“净”长波灵敏度系数订正前后与“遮/不遮”法比较
Table 2 Comparison of shade/unshade method to sum composition method corrected by RNET
表号 型号 RUCS/(μV·W-1·m2) RCCS/(μV·W-1·m2) RSU/(μV·W-1·m2) 百分比误差/% RUCS RCCS 20462 PSP 10.07 10.15 10.21 -1.4 -0.6 20463 PSP 9.50 9.58 9.68 -1.9 -1.0 33734 PSP 7.89 7.98 8.07 -2.2 -1.1 注:RUCS为未修正的成分和法得到的灵敏度;RCCS为热偏移修正后的成分和法得到的灵敏度;RSU为“遮/不遮”法得到的灵敏度。下同。 表 3 使用3种方法计算33734F3灵敏度的比较
Table 3 Comparison of 33734F3 sensitivity using three methods
时间 太阳天
顶角/(°)净热辐射
/(W·m-2)RUCS/
(μV·W-1·m2)RCCS/
(μV·W-1·m2)RSU/
(μV·W-1·m2)百分比误差/% RUCS RCCS 11:27:32 58.6 -137.8 7.77 7.91 7.97 -2.5 -0.8 11:33:32 58.5 -134.5 7.78 7.91 7.97 -2.4 -0.7 11:39:32 58.4 -135.2 7.79 7.92 7.98 -2.3 -0.7 11:45:32 58.3 -135.3 7.79 7.92 7.98 -2.4 -0.7 11:51:32 58.3 -136.5 7.79 7.92 7.98 -2.4 -0.7 11:57:32 58.3 -135.6 7.77 7.91 7.98 -2.6 -0.9 12:03:32 58.3 -136.2 7.78 7.92 8.00 -2.7 -1.0 12:09:32 58.3 -137.0 7.77 7.90 7.98 -2.7 -1.0 12:15:32 58.4 -136.2 7.76 7.90 8.00 -2.9 -1.2 12:21:32 58.6 -136.0 7.76 7.89 7.99 -2.9 -1.2 12:27:32 58.7 -136.2 7.76 7.89 8.00 -3.0 -1.3 12:33:32 58.9 -139.3 7.77 7.91 8.00 -2.8 -1.1 表 4 成分和法用“净”长波方程订正前后与“遮/不遮”法比较
Table 4 Comparison of shade/unshade method to sum composition method corrected by ENIR equation
表号 型号 RUCS/(μV·W-1·m2) RCCS/(μV·W-1·m2) RSU/(μV·W-1·m2) 百分比误差/% RUCS RCCS 20462 PSP 10.07 10.14 10.21 -1.4 -0.7 20463 PSP 9.50 9.56 9.68 -1.9 -1.3 33734 PSP 7.89 7.94 8.07 -2.2 -1.6 36176 8-48 9.54 9.55 9.58 -0.5 -0.3 100180 CMP22 9.34 9.37 9.38 -0.4 -0.1 表 5 成分和法用加盖法订正前后与“遮/不遮”法比较
Table 5 Comparison of shade/unshade method to sum composition method corrected by cap-offset
表号 型号 RUCS/(μV·W-1·m2) RCCS/(μV·W-1·m2) RSU/(μV·W-1·m2) 百分比误差/% RUCS RCCS 33734 PSP 7.89 7.98 8.07 -2.2 -1.2 100180 CMP22 9.34 9.36 9.38 -0.4 -0.2 表 6 成分和法用夜间零点均值法订正前后与“遮/不遮”法的比较
Table 6 Comparison of shade/unshade method to sum composition method corrected by average of zero offset at night
表号 型号 RUCS/(μV·W-1·m2) RCCS/(μV·W-1·m2) RSU/(μV·W-1·m2) 百分比误差/% RUCS RCCS 20462 PSP 10.07 10.10 10.21 -1.4 -1.1 20463 PSP 9.50 9.52 9.68 -1.9 -1.7 33734 PSP 7.89 7.91 8.07 -2.2 -2.0 36176 8-48 9.54 9.53 9.58 -0.5 -0.5 100180 CMP22 9.34 9.35 9.38 -0.4 -0.3 -
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