Practical application of the “turbid water” flag in ocean color imagery: Interference with sun-glint contaminated pixels in open ocean

A simple method to identify turbid, sediment-loaded, waters within satellite ocean color imageries was recently proposed (A. Morel and S. Bélanger, Remote Sensing of Environment, 102, (2006), 237-249). Systematic application of this method to the level-3 composites obtained from three ocean color sensors shows that the “turbid” flag is often raised in the open ocean, especially in the sub-tropical oligotrophic gyres, where turbidity is unlikely. In addition these flagged zones migrate with season, and clearly follow the sun declination course. The combination of low chlorophyll waters with a residual sun-glint is at the origin of this artifact. Simple approaches for eliminating such a misleading detection are proposed. The identification and elimination of the bias are also needed in particular for an unambiguous detection of the presence of calcite (coccolithophores) in open waters.     

国产卫星多角度偏振传感器的光谱特征云检测方法研究

在卫星遥感研究中, 云检测是基础环节, 其结果影响大气、地表各种参数的定量遥感, 同时也影响云微物理特 性的反演。本研究针对多角度偏振卫星载荷(高分五号DPC 传感器), 建立了一种改进的光谱特征云检测算法。该算 法综合利用云像元和非云像元在可见光反射率光谱、氧A 波段吸收、蓝光偏振反射率以及偏振虹等特性上的差异, 分别提出了陆地、海洋上空的云检测方案, 并进一步建立了多角度云检测融合策略以标记云、晴空和未定像元。在 陆地检测中, 通过增加表观压强检测和偏振虹检测分别改进了高层薄云和低层薄云的识别; 在海洋检测中, 利用表观 压强与云层的退偏特性改进了耀光区云像元的识别。全球云检测结果示例显示该算法整体检测效果较好, 同时典型 区域的检测结果与MODIS 云产品也具有较好的一致性。该研究可为高分五号02 星上的多角度偏振传感器云检测提 供方法基础。     

基于海表耀斑中红外基准NPP/VIIRS反射通道在轨验证

将美国NPP卫星可见光红外成像辐射仪(Visible Infrared Imaging Radiometer,VIIRS)的中红外通道(中心波长3.697μm)作为检验基准,使用菲涅尔反射定理建立中红外和被验证通道的海表反射率关系,对四个太阳反射通道(中心波长位于0.672、0.862、1.238和1.602μm)进行了基于海水表面耀斑区反射率精度验证并深入分析该方法的不确定度.结果表明:VIIRS四个通道的验证不确定度分别为3.8%、3.9%、4.1%和4.1%,这一方法可实现VIIRS部分光学通道的在轨较高精度验证.