Harmel Tristan, Chami Malik
Université Pierre et Marie Curie-Paris6, Laboratoire Océanographie de Villefranche, 06230 Villefranche sur Mer, France.
Opt Express. 2008 Apr 28;16(9):6064-80. doi: 10.1364/oe.16.006064.
The influence of oceanic constituents on the polarized reflectance measured at the top of atmosphere (TOA) over open ocean waters in one visible band is investigated. First, radiative transfer modelling is used to quantify the effects of biomass concentration on the TOA polarized signal for a wide range of observation geometries. The results showed that the TOA polarized reflectance remains insensitive to variations in the chlorophyll a concentration whatever the geometrical conditions in oligotrophic and mesotrophic waters, which represent about 90% of the global ocean. The invariance of the polarized signal with water content is explained by the prevailing influence of both atmospheric effects and skylight reflections at the sea surface on the polarization state of the radiation reaching the top of atmosphere level. The simulations also revealed that multidirectional and polarized TOA reflectances obtained in the visible spectrum are powerful tools for the discrimination between the aerosol optical properties. In the second part of the paper, the theoretical results are rigorously validated using original multiangle and polarized measurements acquired by PARASOL satellite sensor, which is used for the first time for ocean color purposes. First, a statistical analysis of the geometrical features of PARASOL instrument showed that the property of invariance of the TOA polarized reflectance is technically verified for more than 85% of viewed targets, and thus, indicating the feasibility of separating between the atmospheric and oceanic parameters from space remotely sensed polarized data. Second, PARASOL measurements acquired at regional and global scales nicely corroborated the simulations. This study also highlighted that the radiometric performance of the polarized visible wavelength of PARASOL satellite sensor can be used either for the aerosol detection or for atmospheric correction algorithms over open ocean waters regardless of the biomass concentration.
研究了海洋成分对开阔海域上空一个可见波段大气顶（TOA）处测量的偏振反射率的影响。首先，利用辐射传输模型量化了生物量浓度对大范围观测几何条件下TOA偏振信号的影响。结果表明，在贫营养和中营养水域（约占全球海洋的90%），无论几何条件如何，TOA偏振反射率对叶绿素a浓度的变化都不敏感。偏振信号随含水量的不变性可以通过大气效应和海面天光反射对到达大气顶层的辐射偏振态的主要影响来解释。模拟还表明，在可见光谱中获得的多方向和偏振TOA反射率是区分气溶胶光学特性的有力工具。在论文的第二部分，利用PARASOL卫星传感器首次获取的原始多角度和偏振测量数据，对理论结果进行了严格验证。首先，对PARASOL仪器的几何特征进行统计分析表明，对于超过85%的观测目标，技术上验证了TOA偏振反射率的不变性，因此，表明从空间遥感偏振数据中分离大气和海洋参数的可行性。其次，在区域和全球尺度上获取的PARASOL测量数据很好地证实了模拟结果。该研究还强调，PARASOL卫星传感器的偏振可见波长的辐射性能可用于开阔海域的气溶胶探测或大气校正算法，而与生物量浓度无关。
