太阳辐射的在轨监测和定标

采用宽视场设计,逐轨扫描太阳式测量方式的FY-3A太阳辐射监测仪,结合在轨一年半的太阳辐照度观测数据和地面实验与理论分析,研究了影响定标精度的因素,给出了修正方程和曲线,并通过与世界辐射基准(WRR)的地面外场定标实验,得到了FY-3A上的三台绝对辐射计的比例系数R1=1.008 3,R2=1.006 6和R3=1.006 5。日地距离的理论分析和实际太阳辐照度测量曲线均证明:地球近日点太阳辐照度值最大,远日点太阳辐照度值最小,且在±3.34%范围内随日期变化。利用天文公式,结合遥感源包中的准确测量时间,给出了日、地修正系数。另外,分析了冷空间背景辐射对定标精度的影响,给出了冷空间辐射值的计算公式,并结合宽视场设计和扫描式测量的特点,重点分析了采光结束时刻和刚捕获太阳光时刻入射角的差异给辐照度测量带来的影响,通过几何关系给出了入射角修正系数方程及修正曲线。最后,综合各定标修正系数,给出了在轨定标方程和定标曲线,并分析了定标精度。

On-orbit Data Calibration of FY-3A Solar Irradiance Monitor

The solar irradiance monitor (SIM), a payload on the FY-3A satellite, is mainly used to monitor the change of solar irradiance. The SIM with wide angle of viewing field scans the sun every orbit. This kind design simplifies the system structure, but makes the on-orbit calibration more difficult. Based on the data obtained by SIM in more than one year, we study the factors that affect the calibration precision experimentally and theoretically, giving the equation and curve. First, by the ground-calibration experiment comparing with the World Radiometric Reference (WRR), we get the scale factors of the three radiometers, R1=1.0083, R2=1.0066 and R3=1.0065. Then, by the theoretical analysis of distance between sun and earth and the data curve of the solar irradiance measured, it is proved that the max solar irradiance is at perihelion (3 January) and the min solar irradiance is at aphelion(3 July), and the solar irradiance changes at the range of ±3.34% with the time variant. Using the astronomical formula and based on the correct time in the remote packages, gets the distance correction factor between sun and earth. It is obvious that the distance between sun and earth affects the calibration precision. In addition, analyzing the affection of the space background on the calibration precision and gets the calibration formula of the space irradiance. Furthermore, combining the characteristics of the wide field of view and the measurement method of step-scanning sun, the effects of the difference from incidence angle between just and over capturing sunlight on the solar irradiation measurement are mainly analysed, geting the the formula of the correction factor and curve with analysing the geometric parameters.Finally analyzing all of correction factors, the on-orbit calibration formula and curve are given.