以固有光学量为核心的二类水体二向性校正模型研究

Water light field has bi-directionality. The bi-directionality correction for water color remote sensing data is one of urgent problems that we have to resolve. For Case I waters, the model for bi-directionality correction is relatively mature, which has been integrated into SeaDAS and applied widely. However, due to the complexity of optical properties in Case II waters including inland waters and coastal waters, the bi-directionality correction model aiming at Case II waters is not mature. The project aims to build a bi-directionality correction model for remote sensing data over Case II waters. Firstly, based on simulated data an inherent-optical-property-centered model will be built to correct the bi-directionality effects in remote sensing reflectance. It is built on a lookup table relying on wavelengths and scattering phase function as its input. Then, a bi-directionality observation device over water surface will be improved and be used to validate the model. Lastly, the model will be coupled with atmospheric radiation transmission model, aiming to construct the bi-directionality correction model facing to satellite remote sensing data, and then it is evaluated. The model will be used to correct the bi-directionality effects in remote sensing data such as wide-coverage satellites with side looking (larger view zenith angle), multi-angle satellites with tilt observation (larger differences in view angles), and geostationary satellite under weak light (larger solar zenith angle). By this model we will obtain more accurate the remote sensing reflectance products in waters.

水体光场具有二向性。水体遥感数据的二向性校正，是水色遥感中一个迫切需要解决的问题。针对大洋一类水体的二向性校正模型相对成熟，已经集成在SeaDAS等系统中并得到较为广泛的应用。但是由于内陆和近岸二类水体光学特性的复杂性，针对二类水体的二向性校正模型还不成熟。本项目旨在构建二类水体遥感数据的二向性校正模型。首先，基于模拟数据构建以固有光学量为核心的反射率二向性校正模型，它是基于以散射相函数为输入项、随波长变化的二向性因子查找表；然后，改进水面以上二向性观测装置并获取实测数据，真实性检验已建的二向性校正模型；最后，将该模型与大气辐射传输模型相耦合，构建卫星遥感数据的二向性校正模型，并评价其精度。该模型可以用于宽幅卫星侧视观测（观测天顶角很大）、多角度卫星倾斜观测（观测角度差异大）、静止卫星弱光照观测（太阳天顶角很大）遥感数据的二向性校正，以得到更为精确的水体遥感反射率产品。

本项目取得的研究进展如下：1）研究了二类水体二向性机理与模型，包括基于Hydrolight模拟了内陆水体光场的二向性、设计了离水辐亮度的多角度测量装置、分析了内陆水体的多角度偏振特性和提取离水辐射、提出了二类水体天空光的水面反射率校正模型；2）发现了高分影像耀斑分布规律和构建耀斑提取算法，并对于如何在高景一号影像采集时就避开耀斑，与资源卫星中心团队初步达成一套流程方法，为高分卫星服务于水色领域提出了避开耀斑这一特殊需求;3）针对国产高分卫星（GF1A/B/C/D、GF2、GF6、高景1-SV1）构建了实用的光学深水前提下的二类水体的遥感反射率反演模型，并利用该模型大规模生产了高分系列卫星监测城市水体的遥感反射率产品，为发展高分卫星的定量化水色产品打下了基础，并基于该定量化产品完成了多个城市的黑臭水体监测；4）针对MODIS构建了二类水体反射率反演模型，提出一种对于覆盖内陆水体MODIS地表反射率产品的简单校正方法，和提出一种MODIS-Terra大气校正算法。