近岸气溶胶散射对水色遥感器辐射偏振校正的影响

With the increasing influences of human activity on ocean environment particularly on the coastal waters, the use of ocean remote sensing for coastal environment monitoring and forecasting receives great attention around the world. To meet the required accuracy of water-leaving radiance products within ±5%, the measurement error introduced by polarization sensitivity of satellite ocean color sensors should be corrected. In polarization correction, neglecting the polarization contributed by aerosol scattering may lead to remarkable overestimation in water-leaving radiances. Over open oceans, where maritime influences dominate, aerosols are generally nonabsorbing and mainly consist of sea salt. While aerosols over coastal waters may consist of strongly absorbing aerosols, such as smoke, which requires to be differentiated. Compared with the open ocean, atmospheric correction of coastal waters is much more complicated due to an incorrect assumption of the marine contribution in the near infrared spectrum. In this work the influence of aerosol scattering on polarization correction of satellite measurements for coastal waters will be studied based on MODIS (MODerate-resolution Imaging spectroradiometer) ocean color bands. A suite of aerosol models over coastal waters will be developed. The polarization correction for atmospheric scattering will be implemented using vector radiative transfer model. Then atmospheric correction over coastal waters will be performed to obtain water-leaving radiance, which will further be validated against SeaWiFS water-leaving radiance products. This research work will provide effective support for monitoring and forecasting coastal waters from Chinese ocean color satellite sensors.

随着人类活动对海洋尤其是近岸水体生态环境的影响日益增加，利用海洋遥感手段实现近岸水体环境监测及预警，受到广泛关注。为了满足离水辐亮度产品精度在±5%以内的应用需求，需要对由传感器的偏振灵敏度引起的测量误差进行校正（以下简称偏振校正）。在校正中忽略气溶胶散射的偏振贡献可能会导致离水辐亮度明显低估。开阔海域的气溶胶模式以非吸收性的海盐气溶胶为主，近岸水体的气溶胶模式可能包含如煤烟等吸收性很强的气溶胶粒子，在传感器偏振校正中需要区分对待。相比开阔海域，近岸水体的大气校正也更为复杂。本项目旨在利用MODIS水色波段分析气溶胶散射对近岸水体遥感辐射偏振校正的影响。建立近岸气溶胶模式库，基于矢量辐射传输模式对传感器观测值进行偏振校正；进而通过近岸水体大气校正得到离水辐亮度产品，并通过SEAWIFS相关产品对其进行验证。本项目的实施可以对我国未来海洋水色传感器更好发挥对近岸水体监测及预警效能提供支持。

随着人类活动对海洋尤其是近岸水体生态环境的影响日益增加，利用海洋遥感手段实现近岸水体环境监测及预警，受到广泛关注。为了满足离水辐亮度产品精度在±5%以内的应用需求，需要对由传感器的偏振灵敏度引起的测量误差进行校正（以下简称偏振校正）。在校正中忽略气溶胶散射的偏振贡献可能会导致离水辐亮度明显低估。开阔海域的气溶胶模式以非吸收性的海盐气溶胶为主，近岸水体的气溶胶模式可能包含如煤烟等吸收性很强的气溶胶粒子，在传感器偏振校正中需要区分对待。相比开阔海域，近岸水体的大气校正也更为复杂。. 本项目旨在利用MODIS水色波段分析气溶胶散射对近岸水体遥感辐射偏振校正的影响。课题首先收集了AERONET近海站点以及圆岛观测站实测的近岸气溶胶观测数据，分析得到典型近岸浑浊水体气溶胶模式库，并分析了粗细例子的非球形对散射相函数和偏振相函数的影响。基于PARASOL多角度偏振数据反演得到的气溶胶光学厚度和气溶胶模式，作为近海浑浊水体偏振校正模型的输入，进而得到近岸离水辐亮度产品。选择2008年1月2日东亚地区近岸MODIS数据进行偏振响应校正，将校正前和校正后的离水辐亮度与SEAWIFS产品进行对比，校正后的MODIS离水反演产品在该区域反演结果与SEAWIFS较为一致，修正了离水辐亮度在日本岛南部显著偏低的现象；并且校正前后与SEAWIFS离水辐亮度产品散点图分析的相关性由0.41提高到了0.66。此外课题还探索了一种基于统计最优化的离水辐亮度反演方法，利用PARASOL多角度偏振数据反演得到了2008年12月全球离水辐亮度（440nm和565nm）。为基于多角度偏振数据反演离水辐亮度产品提供了一个新的思路。. 本项目的实施可以对我国未来海洋水色传感器更好发挥对近岸水体监测及预警效能提供支持。