Application of hyper-spectral remote sensing in monitoring chlorophyll-a concentration 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.gargets.Chlorophyll-a concentration inof 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(R705nm/R680nm) showed close correlation in 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 in 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.