闽江流域福州段悬浮物浓度的遥感分析

Remote Sensing Analysis of Suspended Sediment Concentration Variation of the Lower Min River (Fuzhou Portion) in Fujian of China

利用1996年和2003年两个时相的卫星遥感影像,对闽江流域福州段的悬浮物浓度进行了反演和评估。利用斜率法反演了水体的悬浮物浓度,并通过制作密度分割图和差值影像图来直观地反映1996年到2003年水体悬浮物浓度在时间和空间上的分布变化。研究结果显示,2003年闽江流域福州段的悬浮物浓度几乎在整个河段比1996年有较大幅度的上升。对比上游水质,可以判断悬浮物浓度上升的主要原因是由于上游泥沙携带量增多而引起的。随着近年来福州城市化的快速发展,城市工业废水和生活污水的排放量增加也是部分原因之一。

The human-induced water-quality problem has long been concentrated and intensively studied all over the world.The Min River is the major river system in Fujian province of Southeast China,which runs across the center of the province from west to east and is called 'Mother River' of the province because it provides the drinking water for the 1/3 of the provincial population.However,the water quality of the river has being threatened due to the human activities in the adjacent areas.Therefore,the change of the river water quality needs to be understand for the further protection.Nowadays,there are many methods to study water quality,among which the remote sensing technology is a valuable one employed recently especially in studing historical change of the water quality when the ground-based water measurement data are not available.Therefore,two Landsat TM/ETM+ images of 1996 and 2003 have been used in this study to estimate suspended sediment concentration(SSC) and its variation of the lower stream(Fuzhou portion) of the Min River during the study period.A series of image pre-preccessing methods were first applied to the two raw images,including radiometrical correction and image rectification.Then the open water-covered areas were extracted form the images using the Modified Normalised Difference Water Index(MNDWI). Finally,the slope method proposed by Li et al.(1999) was used to estimated the SSC of the studied river portion.Moreover,the SSC maps of the two study years were further subdivided into 4 concentration-levels using the density slicing technique.So a change detection method could be used to detect spatial and temporal variations of the SSC of the studied river portion during the years from 1996 to 2003.The results reveal that the SSCs have gone up during the 7 study years almost in the whole studied river portion.Comparing with the upper stream of the river,we found that the increase in the SSC was due largely to the heavy suspended sediment loads from the upper river with the contribution of the increasing amount of industrial waste water and civil sewage because of fast urbanization of the Fuzhou City.