Diversity II water quality parameters for 300 lakes worldwide from ENVISAT (2002-2012)

The use of ground sampled water quality information for global studies is limited due to practical and financial constraints. Remote sensing is a valuable means to overcome such limitations and to provide synoptic views of ambient water quality at appropriate spatio-temporal scales. In past years several large data processing efforts were initiated to provide corresponding data sources. The Diversity II water quality dataset consists of several monthly, yearly and 9-year averaged water quality parameters for 340 lakes worldwide and is based on data from the full ENVISAT MERIS operation period (2002–2012). Existing retrieval methods and datasets were selected after an extensive algorithm intercomparison exercise. Chlorophyll-a, total suspended matter, turbidity, coloured dissolved organic matter, lake surface water temperature, cyanobacteria and floating vegetation maps, as well as several auxiliary data layers, provide a generically specified database that can be used for assessing a variety of locally relevant ecosystem properties and environmental problems. For validation and accuracy assessment, we provide matchup comparisons for 24 lakes and a group of reservoirs representing a wide range of bio-optical conditions. Matchup comparisons for chlorophyll-a concentrations indicate mean absolute errors and bias in the order of median concentrations for individual lakes, while total suspended matter and turbidity retrieval achieve significantly better performance metrics across several lake-specific datasets. We demonstrate the use of the products by illustrating and discussing remotely sensed evidence of lake-specific processes and prominent regime shifts documented in the literature.受实际操作与经济成本双重约束，地面采样获取的水质数据在全球尺度研究中的应用存在显著局限。遥感技术是克服此类局限的有效手段，可在适宜的时空尺度下提供全域地表水质的概览信息。 过往多年间，学界已启动多项大规模数据处理项目以搭建配套的数据源体系。本研究的Diversity II水质数据集涵盖全球340个湖泊的多组月度、年度及9年均值水质参数，其数据源自欧洲环境卫星（ENVISAT）搭载的中分辨率成像光谱仪（MERIS）完整运行周期（2002—2012年）的观测资料。 研究团队通过大规模算法比对试验，筛选出了适用于该数据集的现有反演方法与参考数据集。该数据集包含叶绿素a（Chlorophyll-a）、总悬浮颗粒物、浊度、有色溶解有机物、湖泊表层水温、蓝藻及浮植覆盖图等核心产品，辅以多层辅助数据图层，形成了一套通用化规范数据库，可用于评估各类与区域相关的生态系统属性及环境问题。 为开展验证与精度评估，本研究针对24个湖泊及一组涵盖多种生物光学特性的水库，提供了匹配采样对比数据。叶绿素a浓度的匹配对比结果显示，各湖泊的平均绝对误差与偏差量级与其浓度中位数相当；而总悬浮颗粒物与浊度的反演结果在多个湖泊专属数据集上的性能指标则显著更优。 本研究通过阐释与讨论已在文献中记载的湖泊专属过程及显著生态状态转换的遥感证据，展示了该数据集产品的实际应用场景。