内陆河道表层水体反射光谱的走航观测研究

现场水体光谱观测是水体光学性质、水色遥感反演建模等研究不可或缺的基础性工作之一。常规的倾斜观测方法受其较为严格的观测几何条件限制, 需要依据船体位置、太阳方位等不断调整观测角度，特别是针对河道水体光谱观测时，还须考虑河道走向、岸线遮蔽物等情况，因此，只能设置若干站点进行离散样点的观测，难以在岸线环境较为复杂的河道水体开展连续走航快速观测。而现场水体光谱连续走航快速观测能够获取不同地方时的大样本水体反射光谱，丰富对水体二向反射特征的认识，并建立更精确的反演模型，在水色遥感研究中具有极其重要的作用。鉴于此，设计了一种基于垂直观测几何方式的内陆河道表层水体反射光谱连续走航快速观测方法，并通过时空匹配技术获取整个河道的全波长遥感反射率数据。在杭州西小江部分河段的试验表明，该方法获取的遥感反射率与同步实测的叶绿素浓度、浊度等水色组分的相关性较强，选取的特征波段获得的确定系数R2均大于0.855。Sentinel-2的观测天顶角接近于0，近乎于垂直观测。该研究使用Sentinel-2B的光谱响应函数对实测光谱进行等效光谱模拟，转换为相应波段的等效遥感反射率，反演结果与基于Sen2Cor的大气校正后的遥感反射率数据进行建模，分析结果表明，基于Sen2Cor的大气校正后的遥感反射率数据存在高估现象，同时又用Sentinel-2B的大气表观反射率反推辐射亮度，然后用FLAASH大气校正获取Sentinel-2B的遥感反射率数据，经与实测等效遥感反射率建模分析发现，基于FLAASH的大气校正后的遥感反射率数据在小于0.02 sr-1时也存在高估现象，在大于0.02 sr-1时则存在明显低估现象。研究表明，用该方法所获取的大样本实测遥感反射率数据具有对卫星反射率产品进行真实性验证的应用潜力。

Navigation Observation of Reflectance Spectrum of Water Surface in Inland Rivers

In situ measurement of water spectrum is one of the indispensable basic works in the research of water optical properties and watercolor remote sensing inversion modeling. The conventional oblique observation method is restricted by its strict observation geometric conditions, it is necessary to constantly adjust the observation angle according to the position of the ship and the azimuth of the sun, especially for the spectral observation of river water, need to consider the river direction, shoreline shelter and other conditions. Therefore, only a few stations can be set for observation of discrete sample points, it is not easy to carry out rapid observation for continuous navigation in the river water with complex environments around the shoreline. The rapid observation for continuous navigation of the field water spectrum can obtain the reflectance spectrum of large samples of water from different local times, enrich the understanding of the bidirectional reflection characteristics of water, and establish more accurate inversion models, which plays an extremely important role in the study of watercolor remote sensing. Because of this, a rapid observation method for continuous navigation of reflectance spectrum of inland river surface water based on vertical observation geometry is designed in this study, and then obtained the full-wavelength remote sensing reflectance data of the whole river through Spatio-temporal matching technology. The experiments in some sections of XiXiao River in Hangzhou show that the correlation coefficient between remote sensing reflectance obtained by this method and the watercolor components such as chlorophyll concentration and turbidity measured synchronically is strong, the determination coefficients R2 are all greater than 0.855 at the characteristic bands selected in this study. The observation zenith angle of Sentinel-2 is close to 0, close to vertical observation. In this study, use the spectral response function of Sentinel-2B to perform equivalent spectral simulation of the measured spectrum and converts it into the equivalent remote sensing reflectance of the corresponding bands. The inversion result is modeled with the sensing reflectance data after atmospheric correction based on Sen2Cor. The analysis results show that the remote sensing reflectance data after atmospheric correction based on Sen2Cor is obviously overestimated. At the same time, use of Sentinel-2B’s atmospheric apparent reflectance to deduce the radiance, then used FLAASH atmospheric correction to obtain the remote sensing reflectance of Sentinel-2B. By modeling and analyzing the equivalent remote sensing reflectance, the remote sensing reflectance data after atmospheric correction based on FLAASH is also overestimated when it is less than 0.02 sr-1, but obviously underestimated when it is greater than 0.02 sr-1. Research shows that the large sample measured remote sensing reflectance data obtained by this method has the application potential to verify the authenticity of satellite reflectance products.