The Ocean and Land Color Instrument (OLCI) onboard the Copernicus Sentinel-3A satellite is a medium-resolution and multi-spectral push-broom imager acquiring radiance in 21 spectral bands covering from the visible to the far near-infrared. These measurements are primary dedicated to land & ocean color applications, but actually include also reliable information for atmospheric aerosol and surface brightness characterization. In the framework of the EUMETSAT funded study to support the Copernicus Program, we describe the retrieval of aerosol and surface properties from OLCI single-viewing multi-spectral Top-Of-Atmosphere (TOA) radiances based on the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm. The high potential of the OLCI/GRASP configuration stems from the attempt to retrieve both aerosol load and surface reflectance simultaneously using a globally consistent high-level approach. For example, both over land and ocean surfaces OLCI/GRASP uses 9 spectral channels (albeit with different weights), strictly the same prescribed aerosol models and globally the same a priori constraints (though with some differences for observations over land and ocean). Due to the lack of angular multi-viewing information, the directional properties of underlying surface are strongly constrained in the retrieval: over ocean the Fresnel reflection together with foam/whitecap albedo are exclusively computed using a priori wind speed; over land, the Bidirectional Reflectance Distribution Function (BRDF) is slightly adjusted from a priori values of climatological Ross-Li volumetric and geometric terms. Meanwhile, the isotropic reflectance is retrieved globally under mild spectral smoothness constraints. It should be noticed that OLCI/GRASP configuration employs innovative multi-pixel concept (Dubovik et al., 2011) that enhance retrieval by simultaneously inverting large group of pixels. The concept allows for benefiting from knowledge about natural variability of the retrieved parameters.

The obtained OLCI/GRASP products were validated with the Aerosol Robotic Network (AERONET) and Maritime Aerosol Network (MAN) and intercompared with the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and surface products. The overall performance is quite comparable to the community-referenced MODIS. Over ocean the OLCI/GRASP results are encouraging with 67% of the AOD (550 nm) satisfying the Global Climate Observing System (GCOS) requirement using AERONET coastal sites and 74% using MAN deep ocean measurements, and an AOD (550 nm) bias 0.01 with AERONET and nearly zero bias with MAN. Over land, 48% of OLCI/GRASP AOD (550 nm) satisfy the GCOS requirement and a bias within ±0.01 for total and AOD < 0.2. Key challenges are identified and discussed: adequate screening of cloud contaminations, retrieval of aerosol over bright surfaces and in the regions containing complex mixtures of aerosol.

Copernicus Sentinel-3A 卫星上的海洋和陆地颜色仪器 (OLCI) 是一种中等分辨率和多光谱推扫式成像仪，可获取从可见光到远近红外的 21 个光谱波段的辐射。这些测量主要用于陆地和海洋颜色应用，但实际上还包括大气气溶胶和表面亮度表征的可靠信息。在 EUMETSAT 资助的支持哥白尼计划的研究框架中，我们描述了基于大气和表面性质的广义反演从 OLCI 单视多光谱大气层顶 (TOA) 辐射反演气溶胶和表面性质（GRASP）算法。OLCI/GRASP 配置的巨大潜力源于尝试使用全球一致的高级方法同时检索气溶胶载荷和表面反射率。例如，陆地和海洋表面 OLCI/GRASP 都使用 9 个光谱通道（尽管权重不同），严格相同的规定气溶胶模型和全球相同的先验约束（尽管陆地和海洋的观测存在一些差异）。由于缺乏角度多视角信息，下垫面的方向特性在反演中受到强烈限制：在海洋上，菲涅耳反射和泡沫/白帽反照率仅使用先验风速计算；在陆地上，双向反射分布函数 (BRDF) 从气候学 Ross-Li 体积和几何项的先验值略微调整。同时，在温和的光谱平滑度约束下全局检索各向同性反射率。应该注意的是，OLCI/GRASP 配置采用了创新的多像素概念 (Dubovik et al., 2011)，通过同时反转大量像素来增强检索。该概念允许从有关检索参数的自然可变性的知识中受益。2011）通过同时反转大量像素来增强检索。该概念允许从有关检索参数的自然可变性的知识中受益。2011）通过同时反转大量像素来增强检索。该概念允许从有关检索参数的自然可变性的知识中受益。

获得的 OLCI/GRASP 产品通过气溶胶机器人网络 (AERONET) 和海上气溶胶网络 (MAN) 进行了验证，并与中分辨率成像光谱仪 (MODIS) 气溶胶和表面产品进行了对比。整体性能与社区参考的 MODIS 相当。在海洋上，OLCI/GRASP 结果令人鼓舞，67% 的 AOD (550 nm) 满足全球气候观测系统 (GCOS) 的要求，使用 AERONET 沿海站点，74% 使用 MAN 深海测量，以及 AOD (550 nm) 偏差AERONET 的偏差为 0.01，MAN 的偏差几乎为零。在陆地上，48% 的 OLCI/GRASP AOD (550 nm) 满足 GCOS 要求，总偏差在 ±0.01 以内，AOD < 0.2。确定并讨论了主要挑战：充分筛选云污染，