基于0级数据的星载大气痕量气体差分吸收光谱仪在轨衰变监测

大气痕量气体差分吸收光谱仪（EMI）是一种紫外可见成像光谱仪，主要用于实现高空间分辨率的全球每日大气痕量气体浓度反演。EMI在轨运行期间，受空间环境影响，元器件性能随时间推移会不断衰变。为有效监测其衰变状况，利用载荷对地各轨0级数据解析出在轨温度，实现长期在轨温度监测；通过计算各轨道星下点黑暗时的暗背景图像噪声的均值和标准差，实现CCD（charge-coupled device detectors）暗背景噪声随时间变化趋势监测，进一步评估空间粒子对CCD像素点的损伤；利用多次在轨测量的内部白光光源在CCD上的响应，评估CCD探测器在轨像素性能和辐射通量的变化；使用EMI在轨测量的0级太阳光谱数据，结合发射前实验室测试得到的二阶高斯函数模型，用最小二乘法反演在轨仪器光谱响应函数（ISRF），实现仪器光谱响应函数的在轨实时更新；利用石英漫反射板（QVD）、备用漫反射板(RSD)多次测量的太阳光谱，计算石英漫反射板在轨相对衰变因子，修正辐射定标系数，实现漫反射板在轨衰变校正。研究表明，EMI载荷在轨两年以来，温度稳定，各通道暗背景均值年增加率约0.25%～1%，暗背景标准差震荡幅度在1.5%以内；在轨ISRF函数变化幅度约2.3%；内部白光源光路响应变化小于1%，石英漫反射板年衰变率UV2通道小于1.75%，VIS1通道小于1%，VIS2 通道小于0.5%。

On-Orbit Degradation Monitoring of Environmental Trace Gases Monitoring Instrument Based on Level 0 Data

As a kind of ultraviolet-visible imaging spectrometer, the environmental trace gases monitoring instrument (EMI) is mainly used to realize the global daily atmospheric trace gas concentration inversion with high spatial resolution. During the on-orbit operation, the performance of EMI tends to decay with time due to the influence of the spatial environment. In order to effectively monitor its decay condition, the on-orbit temperature is analyzed by using the 0-level data of the load to the ground orbit to realize the long-term on orbit temperature monitoring. By calculating the mean value and standard deviation of the dark background image noise in the satellite points of each orbit, CCD (Charge-Couple Device Detectors) dark background noise variation trend monitoring with time was realized to evaluate further the damage of CCD pixel points caused by space particles. The on-orbit pixel performance and radiation flux of the CCD detectors were evaluated by the response of the internal white light source on the CCD with multiple on-orbit measurements. Using the 0-level solar Spectral data measured by EMI in orbit, combined with the second-order Gaussian Function model obtained from the laboratory test before launch, the Instrument Spectral Response Function (ISRF) is an inversion with the least square method. Real-time on-orbit updating of the instrument’s spectral response function is realized. The on-orbit relative decay factor of the Quartz Volume Diffuser (QVD) and the Reference Solar Diffuser (RSD) were calculated using the Solar spectrum measured many times by the QVD and RSD. The on-orbit decay correction of diffuse reflector plate is realized. The results show that the temperature is stable after the EMI load has been in orbit for two years, the mean annual increase rate of dark background in each channel is about 0.25%～1%, and the fluctuation range of standard deviation of dark background is within 1.5%. The on-orbit ISRF function varies by about 2.3%. The light path response of the internal white light source is less than 1%, and the annual decay rate of QVD is less than 1.75% for the UV2 channel, less than 1% for the VIS1 channel, and less than 0.5% for the VIS2 channel, respectively.