风云卫星载荷反射波段在轨精细化定标模型研究

The radiometric accuracy and stability are the bottleneck problem that restricts the effective application of satellite remote sensed data. In the post-launch calibration analysis of MEdium Resolution Spectral Imager (MERSI) onboard FY-3, periodic oscillations are found. Under the circumstances that the prelaunch and onboard radiometric calibration measurements are insufficient, the high-quality top-of-the-atmosphere radiances simulated by radiometric transfer models are taken as the on-orbit radiometric reference. Various key factors in the process of elaborated radiometric calibration such as temperature, incident angle and polarazation sensitivities, as well as temporal degradation, are separated and studied in order to find their impact mechanism of on-orbit radiometric calibration. The elaborated on-orbit calibration model are constructed including corrections for temporal variation, temperature, incident angle and polarization sensitivities. The parameters of the elaborated model are adjusted synergistically based on the large amount matched radiometric dataset using the optimization method. Based on the fact that the earth system is relatively stable, the long-term radiometric quality of satellite data is diagnosed and evaluated using the spatial-temporal characteristics of ocean color products which are sensitive to radiometric bias. In this project, the on-orbit retrieval method for the elaborated radiometric calibration model will be presented using earth view observations. With the further knowledge about the radiometric characteristics and variation mechanism of the filtered scanning radiometer, the quality of the satellite radiometric observations will be improved, and scientific evidences will be provided to promote the satellite sensor manufacturing and operating.

面向制约遥感应用的辐射精度和稳定度问题，针对风云三号卫星中分辨率光谱成像仪反射波段在轨定标分析数据所体现的周期性震荡现象，在发射前和星上定标测量不足的情况下，以高精度大气顶辐射传输模拟为基准，进行精细化定标关键环节（温度、角度和偏振敏感、时间衰变等）的分解，研究遥感器在轨的温度、角度和偏振的敏感特性，发现反射波段在轨辐射定标的深层次影响机制；建立包括时间趋势校正、温度校正，以及角度和偏振校正等在内的遥感器反射波段在轨精细化定标模型，基于大数据量辐射数据最优化求解，完成精细化定标模型参数的协同调整；并基于地球系统的稳定性，以辐射敏感的海洋反演产品时空特征为参考，完成遥感器长时间序列数据的辐射质量诊断和评估。本研究将建立基于地球目标观测的反射波段精细化辐射定标参数在轨反演方法，深化对遥感器在轨辐射特性的刻画和变化机制的认识，提高遥感器辐射观测数据质量，并为遥感器研制和运行提供科学依据。

随着定量遥感应用对卫星辐射观测数据质量需求的提升，迫切需要深入了解遥感器的辐射响应特性，解决生命期内的高精度、高稳定度定标问题。针对我国极轨气象卫星风云三号的中分辨率光谱成像仪（FY-3 MERSI）的反射波段，基于稳定目标、参考仪器等辐射参考源，结合辐射传输与反演，开展了遥感器反射波段长时间序列在轨精细化定标与辐射质量诊断方法的研究。在发射前和星上定标测量不足的情况下，探究了辐射定标的多个关键影响环节（温度、角度和偏振敏感、时间衰变等），开展了精细化定标模型中各参量的在轨分析与反演方法研究，获得了星上定标灯的在轨变化、遥感器辐射响应的在轨时变、偏振和温度敏感特性，建立了对应的校正模型，提出了在轨暗背景选取的优化方案，揭示了杂散光干扰，并解决了在轨电子学增益异常跳变的识别与归一化个性化问题，形成了较完整的精细化定标模型参数化方案。开展了基于目标大气顶观测模拟比对、参考仪器比对、反演产品特征等的反射波段在轨辐射质量综合诊断分析方法研究，以参考仪器比对重点实现辐射精度评估，以目标大气顶观测模拟重点实现辐射偏差的空间分布特征分析，基于辐射敏感的反演产品对定标误差的放大效应，完成辐射定标结果的应用反馈分析。从严格的单波段辐射精度评估、波段间协同性、辐射偏差的空间分布与时间变化特征分析等方面，形成了较全面的精细化定标质量分析方案，完成了对辐射定标质量的多侧面评估反馈，支撑了再定标模型参数的优化调整。本研究完成了对遥感器在轨辐射特性的刻画，深化了对高可靠辐射定标多环节影响的认识。研究结果除了对现有遥感器进行高精度定标的科学支撑，提高在轨遥感器和长时间历史观测数据质量，还对后续成熟的遥感器（含星上定标器）研制和运行，以及遥感产品应用提供了事实依据与经验参考。