全球先验BRDF知识库的构建及高分辨率地表反照率的反演

The Lack of a high-resolution albedo product has hindered understanding the climate consequences of land cover and ecosystem disturbance. The surface reflectance anisotropy is one of the main factors that restrict the accuracy of high-resolution albedo retrieval from remotely sensed observations. Because of the limitation of the multi-sampling ability of the high-resolution satellite, prior BRDF knowledge usually plays an important role in the inversion process. However, the extraction of prior BRDF knowledge is usually based on statistical methods rather than quantitative analysis. With the quantitative classification ability of Anisotropy Flat index (AFX) to surface reflectance anisotropy, and the six different BRDF types provided by the BRDF archetype, this study plans to learn (1) the effect of surface reflectance anisotropy on albedo retrieval; (2) the correlation of surface reflectance anisotropy with land cover and vegetation index; (3) the method to exactly and rapidly extract prior knowledge of surface anisotropy and to establish a monthly scale global database of prior BRDF knowledge; (4) the method to improve the retrieval of high resolution surface albedo based on prior knowledge of reflectance anisotropy. This study will provide scientific basis for the extraction of prior BRDF knowledge and for the retrieval of high-resolution albedo.

目前，高分辨率地表反照率产品的缺失严重影响了关于地表类型变化及生态系统扰动对气候的影响研究。制约高分辨率地表反照率遥感反演的主要因素之一是地表反射的各向异性特征。由于高分辨率遥感的多角度观测能力十分有限，高分辨率反照率遥感反演通常要借助于先验BRDF知识。但目前先验BRDF知识的提取多是基于统计规律，缺乏定量分析的方法。本项目拟借助于各向异性平整指数（AFX）对地表反射各向异性的定量分类及BRDF原型提供的不同样式的地表反射各向异性特征，研究（1）地表反射各向异性对反照率遥感反演的影响作用；（2）地表反射各向异性与地表类型及植被指数的定量关系；（3）从历史BRDF产品中精确提取先验BRDF知识并建立全球月尺度先验BRDF知识库的方法；（4）根据先验BRDF知识改善中高分辨率地表反照率的反演方法。项目成果将为先验BRDF知识的提取以及中高分辨率地表反照率遥感反演提供科学依据。

地表反照率反映了地球表面对入射太阳短波辐射的反射能力，精确反演地表反照率对陆面过程研究及揭示区域和全球变化的内在机制等都有重要意义。制约高分辨率地表反照率遥感反演的主要因素之一是地表反射的各向异性特征。本项目在BRDF原型的基础上，继续探讨（1）地表反射各向异性对反照率遥感反演的影响作用；（2）地表反射各向异性与地表类型及植被指数的定量关系；（3）从历史BRDF产品中精确提取先验BRDF知识并建立全球月尺度先验BRDF知识库的方法；（4）根据先验BRDF知识改善中高分辨率地表反照率的反演方法。研究表明，地表各向异性反射特征对反照率的影响不可忽略，其与地表类型及植被指数间的关系并不显著，新的BRDF原型提供了更丰富的地表各向异性反射特征，基于中间级别的BRDF原型或基于参数分布概率密度提取的先验知识能有效改善高空间分辨率地表反照率的精度。研究为进一步阐明地表各向异性反射特征对反照率的影响，为改善高分辨率地表反照率的反演提供了理论依据。