北方典型水库型水源地水体叶绿素a含量遥感监测研究

遥感监测具有监测区域广、速度快、省时省力等优势,常用于大面积水质监测。其中,叶绿素a浓度是水质监测的一个重要指标。叶绿素a遥感反演的关键是建立遥感数据和叶绿素a含量的定量关系。本文选取石家庄市饮用水源地黄壁庄水库为研究区域,通过进行水体反射光谱现场测量和同步水质采样,得出研究区水体反射光谱特征,并采用丙酮分光光度法测得各水样中叶绿素a含量。在此基础上通过波段比值模型及一阶微分模型分别分析叶绿素a浓度与反射率之间的线性相关性。结果表明,黄壁庄水库各采样点水体叶绿素a浓度均在4.55μg·L-1以下,光谱反射率比值R705nm/R680nm和696 nm反射率的一阶微分值均与叶绿素a浓度有较显著的线性相关性(r2分别为0.736 6和0.875 5)。本文所得结论与方法可为未来对北方水库型水源地水体进行大面积遥感监测叶绿素a含量提供理论参考。

Application of hyper-spectral remote sensing in monitoring chlorophyll-aconcentration in drinking water source reservoir in North China

Remote sensing has been widely used for water quality monitoring in recent decades. Hyper-spectral remote sensing is a very effective technology for detecting large-scale water eutrophication, which has attracted lots of research in monitoring chlorophyll-a. In this paper, we used hyper-spectral remote sensing technology to present a method for monitoring chlorophyll-a concentration in Huangbizhuang Reservoir in Shijiazhuang, Hebei Province. In-situ hyper-spectral measurements were conducted by using the portable EKO MS-720 spectroradiometer at 10 different points in Huangbizhuang Reservoir, the source of drinking water for Shijiazhuang City and irrigation water for a large area of croplands along Shijin Irrigation Channel. Water samples were also simultaneously collected for laboratory analyses. Sample site position information was recorded via portable GPS. Chlorophyll-a concentration of the water samples were measured in laboratory by Acetone-spectrophotometric. The hyper-spectral data were converted into remote sensing reflectance. Then different band reflectance, reflectance ratio and other reflectance indices were designed and calculated. Linear correlation analysis between chlorophyll-a concentration and spectral reflectance, reflectance ratio and first-order differential of the water sample reflectance were also analyzed and compared. At last, the spectral reflectance ratio model and the first-order differential model were selected based on obtained correlation coefficient and significance. The results showed that Huangbizhuang Reservoir water chlorophyll-a concentration was low, with the highest concentration of 4.55 g·L^-1. It indicated that the reservoir water was in good condition. Spectral reflectance ratio model (R_705nm/R_680nm) showed close correlation with chlorophyll-a concentrations (r² = 0.736 6). On the other hand, the 696 nm first-order differential reflectance model showed a lot more significant correlation with chlorophyll-a concentrations in the entire analytical tests (r² = 0.875 5). This illustrated that the 696 nm first-order differential reflectance model was more effective for chlorophyll-a concentration monitoring in Huangbizhuang Reservoir. Through linear regression estimation, chlorophyll-a concentration in Huangbizhuang Reservoir was generally at the state of oligotrophication. Hence with regard to chlorophyll-a concentration, Huangbizhuang Reservoir water was suitable for domestic, industrial and irrigation use. The method proposed in this work had potential applications in environmental management for improved chlorophyll-a concentration monitoring efficiency in large-scale water bodies. It was also applicable in policy/decision- makings needed for early warning and prevention of water eutrophication.