基于遥感及数值模拟的崇明东滩冲淤与植被关系探讨

RELATIONSHIP BETWEEN MUDFLAT EVOLUTION DYNAMIC AND VEGETATION AT CHONGMING DONGTAN INTEGRATING WITH REMOTE SENSING AND HYDRODYNAMIC MODEL

首先提取多时相卫星影像的水边线信息,借助水动力模型模拟水边线对应时刻的水位,根据水边线水位及实测潮滩高程断面推算潮滩的高程及冲淤变化信息,同时利用高分辨率遥感影像(Quick Bird)对潮滩植被进行模糊分类及变化监测,并通过植被覆盖度指数及现场观测数据反演植被的发育程度信息。依据上述计算结果探讨了崇明东滩冲淤变化与植被及潮间带高程的关系。结果表明在崇明东滩中低潮滩附近存在冲淤峰值,由峰值位置向海向陆侧递减。年平均沉积速率与潮滩高程(<3.4m)的相关性R2=0.8 106。中低潮滩出现最大沉积速率主要是受植被的捕沙作用及沉积滞后的影响,高潮滩沉积速率较小则归因于高潮滩淹水机率相对较小导致泥沙在高潮滩落淤量降低,相反低潮滩则由于高程较低加之缺少植被保护沉积速率较小。结果同时表明由于南北部潮滩动力条件及植被状况的差异导致崇明东滩从北部滩面、中部滩面到南部滩面冲淤峰值出现的高程各不相同。总之,遥感技术结合水动力模型能够较方便地得到滩涂相关环境因子信息,克服了常规测量的困难,为分析海岸带冲淤变化动态提供了新的技术手段。

Hydrodynamic model was investigated to assign corresponding elevation of waterlines,which were extracted from multi-temporal Landsat TM images at Chongming Dongtan,China.And the mean sedimentation rates were calculated at four transects in combination of waterlines with heights and situ measurement.Salt marsh vegetation classification was made through the integration of auxiliary data with remote sensing based on fuzzy mathematical theory.On the basis of vegetation investigation,fractional vegetation cover（FVC）was derived from high resolution Quick Bird images to indentify vegetation coverage.Then the effects of vegetation and elevation on sedimentation were discussed according to the above derived information.The results revealed that sediment accretion showed a shoreward and offshore reduction from the maximum site at the four profiles.A positive relationship was demonstrated between the mean accretion rates and surface elevation of low marsh and mudflat（R2=0.8106）.The hydrodynamic attenuation by vegetation and the effect of settling lag on suspended sediments were likely to result in a peak vertical accretion in the low marsh.The shoreward decrease in accretion from the peak site could be attributed to the low settling potential of fine-grained suspensions resulted from the reduction in submergence frequency over the swamps.The offshore decreasing and negative accretion,however,could be related to the relative lower elevation and lack of vegetation.Spatial changes in sedimentation rate were also striking at the same elevations of different profiles,which could be attributed to differences in vegetation growth and hydrodynamics.In a summary,the synoptic capability of remote sensing integrating with hydrodynamic model provides a useful tool to facilitate field surveys,which may lead to better understanding of coastal processes.