星载EMI在轨光谱定标方法研究

On-Orbit Spectrum Calibration of Spaceborne EMI

于2018年5月9日搭载高分五号卫星发射的大气痕量气体差分吸收光谱仪(EMI)为紫外可见波段高分辨率成像光谱仪。为考察其在轨光谱性能,首先采用波长寻峰法即以太阳Fraunhofer线作为特征峰以快速获取载荷的光谱范围,然后采用谱线匹配法获取载荷空间维度的光谱弯曲值,最后采用光谱拟合法获取光谱分辨率的变化。寻峰法通过与标准Fraunhofer线进行比对找寻特征峰,得到其标准波长及对应像元,经二阶多项式拟合可得到像元-波长对应关系。谱线匹配法通过Pearson相关系数法作为判据,即利用两谱线之间相关系数作为匹配结果的判断条件,得到测量谱线与标准谱线间的偏移值,定标结果满足定标精度高于0.05 nm的要求。光谱拟合法通过求解将测量谱与高分辨率太阳参考谱拟合,可以分析光谱分辨率变化。对2019年1月7日全天15轨数据的分析结果表明,光谱分辨率在一天内的变化一致,其单行标准差不超过0.01,因此在之后仪器长时间运作或受到干扰情况下,利用此方法对其性能衰变进行分析具有重要意义。

The environmental trace gases monitoring instrument(EMI)launched on the Gaofen-5 satellite on May9,2018 is a high-resolution imaging spectrometer in the UV-visible band.In order to investigate its on-orbit spectral performance,the wavelength peak searching method was first adopted,namely,the solar Fraunhofer line was used as the characteristic peak to quickly obtain the spectral range of the load,then the spectral curve value of the load space dimension was obtained by using the spectrum-matching method,and finally the spectral fitting method was used to obtain the change of spectral resolution.By comparing with the standard Fraunhofer,the peak searching method can find the characteristic peak and obtain the standard wavelength of the peak and the corresponding pixel,and then the corresponding relationship between pixel and wavelength can be obtained by second order polynomial fitting.The Pearson correlation coefficient method is used as the criterion for spectral-matching method,that is,the maximum correlation coefficient between two spectral is used as the condition for the optimal matching result,and then the offset value between the measured spectral and the standard spectral is obtained.The calibration result satisfies the requirement that the calibration precision is higher than 0.05 nm.The spectral fitting method can analyze the change of spectral resolution by solving and fitting the measured spectrum with the high-resolution solar reference spectrum.The analysis results of the all-day 15-track data on January 7,2019 show that the change of spectral resolution is consistent within a day,and the single row standard deviation is less than 0.01.Therefore,it is of great significance to analyze the performance decay of the instrument in the case of long-term operation or interference.