辐射校正场光谱反射率的直接法观测与自校准技术研究

On-orbit field calibration is a basic method to correct the responsivity change of the satellite sensors, and surface reflectance is one of the key input parameters of field calibration. To meet the increasing requirements of quantitative applications of the satellite data at present, the impact of the spectral reflectance indirect measurement which is based on reference panel on the uncertainty of field calibration need to be resolved and removed urgently. In order to upgrade the long-term precision of the surface reflectance, the direct-method measurement and self-calibration technology of the spectral reflectance is suggested in this proposal. First, realizing the direct measurement of surface reflectance by building a special optical system based on the cosine corrector and observation lens to measure the total sky irradiance and surface radiance, where the problem of high-dynamic-range throughput in these two optical paths should be resolved. Second, conducting the research on self-calibration technology of surface reflectance measurement to achieve the high accuracy reflectance observation and guarantee the long-term consistency, with the solar direct irradiance result which is measured by the same observation lens as the surface radiance, the problem of accurate ratio-transmittance calibration in the system should be solved in this process. Third, Guaranteeing the uncertainty of the new measurement method to be less than 1% through the system-level calibration in the laboratory, and evaluating the accuracy improvement result of the surface reflectance measurement by this new method through the on-orbit field calibration experiments.The implement of the project is expected to build the foundation for the high precision calibration and guarantee the long-term data consistency of the satellite remote sensors. The research achievements can prospectively provide technical support for the field calibration of space observation systems in China.

卫星载荷在轨场地定标是校正星载遥感器响应度变化的基本手段，地表反射率是场地定标的关键输入参数之一，针对目前卫星数据定量化应用需求的提升，迫切需要解决基于参考板的地表反射率间接测量对场地定标不确定度的影响。为提升地表反射率的长期观测精度，项目开展校正场反射率直接测量方法和自校准技术研究。（1）研究单光学系统测量天空总照度和地表辐亮度的技术方法，设计以余弦校正器和观测镜头为核心的前置光学系统，解决双光路大动态范围光通量匹配难题，实现地表反射率的直接法观测。（2）开展基于太阳直射的反射率观测自校准技术研究，解决系统比值透过率定标问题，实现地表反射率长期观测精度的一致性。（3）实验室系统级定标保障地表反射率测量不确定度优于1.0%，校正场在轨定标比对试验评估直接法测量精度的提升效果。项目的开展将为卫星遥感器的高精度定标和数据一致性奠定研究基础，为我国正在构建的空间观测体系提供在轨场地定标技术支撑。

为了适应光学遥感器的地面定标技术需求，国内外均提出了建设定标场网络的计划，需要研发和布设无人值守和智能化运行的地面定标终端平台，形成遥感卫星高频次、高时效的地面定标和互定标能力，以此实现及时校正载荷衰变，提升定标精度的科学目标。针对基于参考板的地表反射率间接测量对场地定标不确定度的影响，项目开展了校正场反射率直接测量方法和自校准技术研究。1）项目完成了整体方案和测量流程的设计，并设计了四种不同的观测模式，实现了总照度观测、辐亮度观测、辐射自校准观测、光谱自定标；2）以前置光学系统的设计为核心，完成了余弦校正积分球、对地观测镜头、自校准系统、太阳跟踪系统的设计，完成了系统的总体装配；3）通过不同观测模式下的光通量模拟，解决了辐照度和亮度的同步观测、辐射与波长自定标、光辐射动态大动态范围的计算等技术难题，实现了一个数量级内的光通量匹配；4）通过设计基于太阳直射的双模式观测方式，实现了光学系统比值透过率的自校准，并实现了波长自校准；5）完成了测量系统的实验室光谱定标和反射率观测精度定标，获得的反射率观测精度不确定度为0.92%；6）设备样机开展了野外观测比对测试，不同设备的漫总比绝对偏差优于0.01，地表反射率的比对结果优于5%，光谱定标精度在1nm之内，验证了反射率直接观测和自校准的可行性和精度水平。项目最终实现了大气传输特性、地面入射辐照度与反射辐亮度等多项参数的同步观测，为自动化地面定标平台的研发奠定基础。