基于卫星反演的ForelUle水色指数(FUI)可以在大的时空尺度上表征水质的综合特征。MODIS地表反射率产品(MODIS-500m)的高频观测和丰富的历史数据为内陆湖FUI监测提供了重要的数据支持。然而,MODIS-500米在可见光范围内只有三个波段,导致FUI反转存在显著的不确定性。为了解决这个问题,本研究使用覆盖天然水域的500个合成光谱建立了改进的FUI反演模型。模型,性能阈值设置为170°(FUI=8),在整个颜色空间中使用了分段算法。使用现场测量数据集(3500个样本)进行验证,该模型表现出优异的性能,平均相对误差(MRE)和均方根误差(RMSE)分别为1.71%和3.63°,分别。与现有模型相比,它更适合各种类型湖泊的长期FUI倒置,特别是在富营养化地区。随后,将该模型应用于2000年至2022年的MODIS-500m观测,揭示了中国180个大型湖泊和水库(以下简称湖泊)的FUI时空动态。结果表明,研究区的长期平均FUI为9,西部和东部地区为7和12,分别,西蓝、东绿的空间分布明显。所有湖泊的色相角平均变化率为-0.085°/年,呈现总体下降趋势。使用多重一般线性模型(GLM)量化了环境因素对每个湖泊地区长期水色变化的相对贡献。尽管每个湖区表现出不同的驱动力,它们主要受到植被的影响,湖泊表面积,和人为因素。此外,分析了湖泊水色的季节性类型,西方和东方呈现出相反的模式,反映了地形特征和气候季节变化对水色的显著影响。研究结果为利用MODIS-500m数据准确反演FUI提供了技术,同时加深了对中国内陆湖泊长期水色变化的认识。
The Forel Ule water color index (FUI) based on satellite inversion can characterize the comprehensive characteristics of water quality on a large spatiotemporal scale. The high-frequency observations and rich historical data of the MODIS surface reflectance product (MODIS-500 m) provide important data support for monitoring the FUI of inland lakes. However, MODIS-500 m has only three bands in the visible light range, resulting in significant uncertainty in FUI inversion. To address this problem, this study developed an improved FUI inversion model using 500 synthetic spectra covering natural waters. The model, with a performance threshold set at 170° (FUI = 8), used a segmented algorithm across the entire color space. Validated with on-site measurement datasets (3500 samples), the model exhibited excellent performance, with mean relative error (MRE) and root mean square error (RMSE) of 1.71 % and 3.63°, respectively. Compared to existing models, it was more suitable for long-term FUI inversion in various types of lakes, particularly in eutrophic regions. Subsequently, the model was applied to MODIS-500 m observations from 2000 to 2022, revealing the spatiotemporal dynamics of FUI in 180 large lakes and reservoirs (hereinafter referred to as lakes) in China. The results indicated that the long-term mean FUI in the study area was 9, with 7 and 12 in the western and eastern regions, respectively, showing a distinct spatial distribution of \"blue in the west and green in the east.\" The mean change rate of hue angle for all lakes was -0.085°/yr, showing an overall decreasing trend. Environmental factors\' relative contributions to long-term water color changes in each lake region were quantified using the multiple general linear model (GLM). Although each lake region exhibited different driving forces, they were primarily influenced by vegetation, lake surface area, and anthropogenic factors. Additionally, the seasonal types of lake water color were analyzed, with the west and east showing opposite patterns, reflecting the significant influence of topographic features and seasonal changes in climate on water color. The research results provide techniques for accurate inversion of FUI using MODIS-500 m data, while deepening the understanding of long-term water color changes in inland lakes in China.