长江口水质MERIS卫星数据遥感反演研究

【目的】获取准确的水质参数分布情况,进而对水质参数与动力作用复杂的河口水域环境进行综合评价。【方法】利用2011年5月30组长江口水域的遥感反射率数据,在尝试多种波段组合以及不同函数形式后,针对叶绿素a浓度和总悬浮物浓度分别建立最优经验反演模型。【结果】对总悬浮物浓度,波段差值(634~644nm)的二次函数形式最优,决定系数R~2为0.837,均方根误差(RMSE)为0.226mg·L~(-1),利用独立的验证样本得到平均绝对百分比误差(MAPE)为58.2%。对叶绿素a浓度,波段比值(650nm/644nm)的二次函数形式最优,R~2为0.552,RMSE为0.486mg·m~(-3),利用独立的验证样本得到MAPE为66.2%。将模型运用于2011年5月MERIS卫星数据,反演出长江口水域叶绿素a浓度与总悬浮物浓度空间分布图,叶绿素a浓度呈现出从河口向外海逐渐减少的趋势,最大值出现在舟山群岛附近。总悬浮物浓度呈阶梯状向外海减少。【结论】通过评价参数可看出,总悬浮物浓度反演模型对总悬浮物浓度反演效果较为准确,而叶绿素a浓度反演模型显示对叶绿素a的反演浓度较低。

Water Quality Retrievals from MERIS Satellite Data in Yangtze Estuary

[Objective]In order to grasp the distribution map of water quality parameters more accurately,we evaluate the estuary which has complex dynamical system.[Methods]After using 30 in situ remote sensing reflectance data collected in May 2011 and trying many kinds of band combinations and function forms,the optimal empirical models for chlorophyll-a concentration and total suspended matter concentration were established.[Results]For total suspended matter concentration,Quadratic function model by band difference(634~644 nm)performs best,of which coefficient of determination (R2 )is 0.837 and root mean square error (RMSE)is 0.226 mg·L-1 .In the model validation,the mean ab-solute percentage error(MAPE)by using the in-dependent dataset shows a value of 58.2%.For chlorophyll-a concentration,quadratic function model by band ratio (650 nm/644 nm)performs best,of which coefficient of determination (R2 ) is 0.552 and root mean square error(RMSE)is 0.486 mg·m-3 .In the model validation,the mean absolute percentage error (MAPE)by u-sing the independent dataset shows a value of 66.2%.The MERIS satellite data in May 2011 were evaluated by the models,and the distribu-tion map was obtained for spatial concentration of chlorophyll-a and total suspended matter of the Changj iang Estuary through simulation.There was a trend that the concentration of chloro-phyll-a decreased gradually from the estuary to the sea,and the maximum value appeared in the Zhoushan Islands.The concentration of total suspended matter reduced stepwisely to the sea.[Conclusion]As is shown in the evaluation parameters,the total suspended matter concentration model has accurate effect in retrieve water quality while the chlorophyll-a concentration model has lower effect.