基于实测光谱分析和MODIS数据鄱阳湖叶绿素a浓度估算

基于遥感的大面积水体监测技术为水环境监测提供了一种有效手段。以鄱阳湖为研究区，以反映水体营养状态的重要指标叶绿素a为研究对象，在测定研究区水体光谱及叶绿素a浓度和收集了相应时间的MODIS数据的基础上，采用浮游藻类指数法（Floating Algae Index，FAI）提取鄱阳湖水体范围，对鄱阳湖水体实测光谱数据进行剔除异常、归一化及光谱微分处理，构建波段差值、比值、归一化差值等光谱指数，利用最小二乘原理迭代分析水体叶绿素光谱响应特征，得出敏感波段范围：673～680 nm与650～665 nm、680～710 nm与650～670 nm、662～671 nm与700～720 nm光谱区间组合。选择最佳通道组合，建立基于MODIS影像的鄱阳湖叶绿素a浓度反演模型，相关系数为067。应用该模型得到2011年秋季鄱阳湖的叶绿素浓度估算值，反演结果显示湖区水体叶绿素浓度总体不高，且在空间分布上湖区水体周边与陆地交界处比湖中心区浓度偏高。分析认为：通过对实测光谱的定量分析，获得对鄱阳湖地区水体叶绿素浓度的光谱特征认识，揭示出其反射光谱的长波漂移现象，为鄱阳湖这一富营养化程度底，且水体分布不均匀区域建立一种叶绿素浓度反演方法，可为该区域长期的水环境管理提供方法借鉴

ESTIMATING CHLOROPHYLL-A CONCENTRATION IN POYANG LAKE USING MODIS BASED ON MEASURED REFLECTANCE SPECTRA

It is an efficient method of water environment survey to using remote sensing data for large area water quality monitoring.The Poyang Lake was selected as the research area in this research. The chlorophyll a content which gives an important index to eutrophic state of water was chosen as the study object. The water reflectance spectra were acquired with an ASD FieldSpec HH (350 1050nm) and the MODIS data collected during the same period. Based on MODIS data, the range of the Poyang Lake was extracted by a approach named Floating Algae Index (FAI).After the measured spectra were preprocessed with deleted abnormal data,normalization and Spectral derivative,the relation between the spectral reflectance of the Poyang Lake and the corresponding moment of the chlorophyll a concentration were analyzed in spectral index method which was structured by band difference,ratio and the normalized JP2]difference.The sensitive band scope
was harvested,including the band intervals of 673-680 nm and 650-665 nm,680-710 nm and 650-670nm,662-671 nm and 700-720 nm. Then the optimum bands combination JP]was chosen. At last the inversion model of MODIS data for chlorophyll a concentration of the Poyang Lake was achieved,and the correction coefficient was 0.67. Applying the model,the chlorophyll a concentration distribution map of the Poyang Lake in the autumn of 2011 was given. The result showed that the chlorophyll a concentration of the Poyang Lake was not high,and in spatial distribution the chlorophyll a concentration was higher at the border of water and land than at the center of lake. The analysis supports that the spectrum of the Poyang Lake has been known by quantitative analysis of the measured spectra,and the long wave drift of spectral reflectance phenomena is revealed. A method of remote sensing to monitor chlorophyll a concentration the for Poyang Lake which is of low eutrophication and unevenly distributed is established. Meanwhile it provides a forceful scientific guidance for water environment management of the Poyang Lake