海洋上空云多角度偏振辐射阈值检测方法研究

Multi-Angle Polarization Radiation Threshold Detection Method of Cloud Cover Over Ocean

云是海洋遥感的一项重要研究内容,云检测精度对于海洋上空云微物理特性的反演和海洋水体观测具有重要意义。以高分五号卫星搭载的大气气溶胶多角度偏振探测仪(Directional polarimetric camera,DPC)在轨成像数据为研究对象,提出了一种基于多角度偏振辐射信息的海洋上空云检测方法。首先用耀光角判别法区分出海洋耀光区域和非耀光区域,然后利用多角度偏振信息对耀光区域进行云检测,并基于反射率阈值、可见近红外反射率比值和偏振信息检验等方法对非耀光像元进行云检测。以印度洋和大西洋海域为例,基于DPC数据进行了海洋上空云检测,经过时空匹配后,其结果与MODIS(Moderate-resolution imaging spectroradiometer)云掩膜数据一致性分别为91.39%和94.73%。此外,用法国POLDER3(Polarization and directionality of the earth′s reflectances)数据验证了文中算法的有效性,将云检测结果和POLDER3官方云检测产品对比,一致性达到90.40%。文中提出的多角度偏振辐射阈值云检测算法,可为卫星观测的海洋上空云特性研究和海洋水体观测提供有效云检测数据。

Clouds are important in ocean remote sensing detection,and cloud detection accuracy is significant to the inversion of cloud microphysical characteristics over ocean and the observation of ocean water body.By using the on-orbit imaging data of the atmospheric aerosol multi-angle polarization detector(directional polarimetric camera,DPC)onboard GF-5,a detection method for cloud cover over the ocean based on multi-angle polarization radiation information is proposed.Firstly,the sunlight angle discrimination method is used to distinguish the ocean glint area and the non-glint area.Then the multi-angle polarization information is used to detect cloud in the ocean glint area,and on the other hand,the methods of reflectance threshold,the visible-near infrared reflectance ratio and the polarization information inspection are used to detect cloud in the non-glint aeras.Taking the Indian Ocean and the Atlantic Ocean as experiment aeras,cloud detection over the ocean was carried out based on DPC data,then the results were compared with MODIS(Moderate-Resolution Imaging Spectroradiometer)cloud mask data,and the consistency reaches 91.39%and 94.73%respectively.In addition,the data of French POLDER3(polarization and directionality of the earth′s reflectances)is also used to verify the effectiveness of the proposed algorithm in this work,and the consistency between the cloud detection results and the official POLDER3 cloud detection productsreaches 90.40%.It is believed that the multi-angle polarization radiation threshold cloud detection algorithm proposed in this work can provide effective cloud detection data for satellite observation of cloud characteristics over the ocean and ocean water observation.