极轨气象卫星红外通道太阳污染时相规律与订正模型研究

The solar impingement into the sensors will lead to severe contaminations on calibration systems and earth scenes when the polar orbiting spacecrafts come in or out of the terminator of each orbit around high latitude. This solar contamination is common problem on space-borne optical payloads of domestic polar orbiting meteorological satellites. This study focuses on the research of apparent features and spatio-temporal variations of solar contamination, then try to find its internal and external sources of the formation and seasonal variation mechanisms. This study will establish an algorithm to discriminate the contaminated data by solar. For the abnormal mode of solar contamination on calibration targets (blackbody and cold space view) and earth scenes, we mainly assess its effect on the calibration accuracy and uncertainty of the infrared bands. A calibration error model is established by simulating the variation of the solar illumination on instruments in different orbit positions and consequent reflective contamination and blackbody temperature gradients. This model will also combine internal non-equilibrium thermal model and heat transfer of the blackbody. The correction model and method of solar contamination will be developed for the infrared bands based on the abnormal increase of the reflective radiation in mid-infrared band, blackbody temperature gradient and wrong space-view clamp. we plan to conduct the contamination correction by using these methods such as FFT transformation and EMD method to accurately filter and decompose the signals which was contaminated by solar impingement. Based on these procedures, one can establish the real-time dynamic correction model for solar contamination. This study can not only pave the theoretical and technique basis for improving the operational calibration algorithm, but also establish a better recalibration processing for satellites historical data.

极轨卫星在高纬昼夜交替时太阳光会进入遥感器内部，造成定标系统和图像的严重污染。本研究针对风云极轨卫星光学载荷普遍存在的太阳污染共性问题，开展其表现特征和时空变化规律探索研究，寻找污染形成的内外部根源和季节变化机理，研究污染数据的自动甄别方法。针对太阳污染导致定标源（黑体冷空）和图像的异常特征模态，重点评估它对红外通道定标精度的影响和不确定性。模拟太阳在轨道不同位置对仪器部件照射变化，及由此形成的反射污染和黑体温度梯度，结合黑体内部热力非平衡传递模型，建立太阳污染与定标误差关联模型。开展红外通道太阳污染的订正模型与方法研究，针对污染导致的太阳反射增大、黑体温度梯度、冷空钳位污染等方面建立订正算法，采用快速傅立叶变换FFT和经验模态分解EMD等数据处理方法，实现定标过程中对污染的准确过滤和本征模态分解，建立太阳污染实时动态订正模型，为业务定标算法改进和卫星历史数据重新再定标奠定理论和技术基础。

本研究就我国极轨气象卫星光学载荷红外通道展开太阳污染机理研究，分析地球观测和定标数据被太阳污染发生的时空变化规律，建立红外通道太阳污染的订正模型和精度验证方法。这种太阳污染不仅发生在高纬度晨昏过渡区域，是NWP卫星资料同化和气候敏感区域（特别是北极附近），精确的太阳污染订正将较大改善数据天气预报效果，而且类似的污染问题在即将发射的晨昏轨道卫星将更为致命，为晨昏轨道卫星防污染设计和污染数据订正提供宝贵经验。本研究的成果不仅可以改进在轨业务运行卫星定标算法，提高红外通道定标精度、数据质量和数据应用效率，而且对于历史长时间序列数据集统一辐射再定标提供订正算法，促进长序列卫星数据的气候应用。此外太阳污染问题将在晨昏轨道上显得尤为突出，该研究对于晨昏轨道卫星的定标算法建立和杂散光去除提供非常基础性的前沿预研。太阳污染的机理研究对未来遥感仪器改进设计提供宝贵参考依据，促进我国仪器载荷研制水平的提高。.本项目对于同类卫星仪器观测精度和数据质量的深入研究开展提供帮助和借鉴，提高我们对遥感仪器在轨运行变化规律的认识，提升观测数据的定标精度和数据质量，促进遥感数据的定量应用水平，为空间载荷研制质量提高提供宝贵分析经验。另外本研究的进行对于气象卫星长时间序列历史数据重新再处理和辐射再定标提供订正算法和质量控制方法，为长序列卫星数据气候研究打下坚实基础。