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摘要:太阳辐射测量是研究太阳活动与地球气候演变的重要方式之一,对人类社会的可持续发展具有重要意义。衍射效应作为测量过程中系统误差的主要来源之一,有必要进行精确的修正,从而提高测量数据的精度。首先,对衍射效应理论进行研究,从Kirchhoff衍射理论出发,在高斯光学近似下,逐步确定点与点,点与面,面与面之间的能量传输关系,推导出了衍射效应的一般公式;接着,根据衍射效应的渐近性质,得到了一种简化的计算方法;然后,用简化的方法计算太阳辐照绝对辐射计(SIAR)的衍射效应以及衍射修正因子,最后,根据衍射修正结果,计算相对于世界辐射基准(WRR)的定标系数。结果显示:SIAR的衍射效应以及衍射修正因子分别约为1.002 742和0.997 265。经过衍射修正后,SIAR对WRR的定标系数更接近于1,表明衍射修正降低了系统误差,提高了辐射测量的准确度。Abstract:Solar radiation measurement is one of the important way to study solar activity and evolution of Earth's climate, which is of great significance to the sustainable development of human society. As one of the main sources of systematic errors in the measurement, diffraction effect must be accurately corrected so as to improve the reliability of the measurement data. China has little research on the diffraction effects in solar radiometers, and there are currently no related corrections. With the increase demand of the accuracy of solar radiation measurements, it is necessary to systematically study the diffraction effect. Firstly, the diffraction effect theory is studied. According to the Kirchhoff diffraction theory as well as the Gaussian optical approximation, the energy transfer relations between points and points, points and faces, and between faces is gradually determined, and the general formula of diffraction effect is derived. Then a simplified calculation method is obtained according to the asymptotic property of the diffraction effect. The diffraction effect of the Solar Irradiation Absolute Radiometer (SIAR) and the diffraction correction factor are then calculated through a simplified method. Finally, based on the diffraction correction results, the scaling factor relative to the World Radiation Reference (WRR) is calculated. As a result, the diffraction effects and diffraction correction factors of SIAR are about 1.002 742 and 0.997 225, respectively. In addition, the calibration coefficient of SIAR for WRR is closer to 1, indicating that the diffraction correction reduces the systematic error and improves the accuracy of the radiation measurement.
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表 1几种太阳辐射计的衍射效应
Table 1.Diffraction effects in some radiometers
Instrument Ra/mm dd/mm Rd/mm Correction PMO6V 4.25 95.4 2.5 1.001 280 DIARAD 6.52 144 4.001 5 1.000 833 ERBE 12.09 100.8 4.039 1.000 209 ACRIM Baf1 6.654 8 150.469 6 3.987 8 1.000 828 Baf2 6.311 9 76.352 4 3.987 8 1.000 466 Total 1.001 295 TIM 3.989 4 101.6 7.62 0.999 582 表 2采用简化方法的衍射效应值
Table 2.Diffraction effects by using simplified method
太阳辐射计 衍射效应 F Cdiff=F-1 δ RMO6V 1.001 229 0.001 299 +0.000 010 DIARAD 1.000 807 0.000 807 -0.000 026 ERBE 1.000 204 0.000 204 -0.000 005 ACRIM Baf1 1.000 793 0.000 793 -0.000 035 Baf2 1.000 450 0.000 450 -0.000 016 Baf3 1.001 242 0.00 1242 -0.000 053 TIM 0.999 577 -0.000 423 -0.000 005 表 3SIAR的SAD参数
Table 3.SAD parameters of the SIAR
光阑 光阑半径R/mm 光阑与探测器距离dd/mm 探测器(主光阑)半径rd/mm Ap1 5.75 100 4.00 Ap2 5.40 80 4.00 Ap3 5.05 60 4.00 Ap4 4.70 40 4.00 Ap5 4.35 20 4.00 表 4SIAR的衍射效应
Table 4.Diffraction effects in SIAR
光阑 衍射效应F ε=F-1 Ap1 1.000 785 0.000 785 Ap2 1.000 692 0.000 692 Ap3 1.000 577 0.000 577 Ap4 1.000 435 0.000 435 Ap5 1.000 252 0.000 252 Total 1.002 742 0.002 742 表 5衍射效应未修正的WRR Factor
Table 5.Diffraction effects uncorrected WRR Factor
SIAR型号 定标系数WRR Factor |WRR Faotor-1| SIAR-2C 0.998 949 0.001 051 SIAR-4A 0.998 445 0.001 555 SIAR-4B 0.996 734 0.003 266 SIAR-4D 0.995 917 0.004 083 表 6衍射修正过的WRR Factor
Table 6.Diffraction effects corrected WRR Factor
SIAR型号 定标系数WRR Factor |WRR Factor-1| SIAR-2C 1.001 688 0.001 688 SIAR-4A 1.001 182 0.001 128 SIAR-4B 0.999 467 0.000 533 SIAR-4D 0.998 648 0.001 352 -
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