基于遥感的九段沙湿地DEM构建及动态变化分析

DEM construction and dynamic change analysis of J iuduansha wetland based on remote sensing

对九段沙湿地1987年、2001年和2004年多个时相的Landsat遥感影像提取了多组水陆边界点,并依据四周4个潮位站的潮位观测值,用距离倒数权重法计算了各组边界点的高程。结合相应年份长江口海图九段沙区域的水深数据,构建了九段沙湿地3个年份的数字高程模型。统计时比分析结果表明,目前九段沙湿地0 m线以下部位的淤积速度显著下降,-6 m线部位已开始蚀退;另一方面,0 m线及以上湿地部位的淤积速度仍有所加快。

Jiuduansha wetland is a typical island surrounded by water region in the Yangtze estuary, and it is one of important land resources of Shanghai, so its evolvement has attracted much attention. The multigroup instantaneous border points between water and land of Jiuduansha wetland have been identified from multi-temporal Landsat images, and their elevations have been computed by inverse distance weighted interpolation algorithm according to the tide levels of the four surrounding tide stations. And combining with the depth data of the Yangtze estuary chart, three DEMs of Jiuduansha wetland have been created. Statistic data suggest that Jiuduansha wetland has a quite different tendency on dynamic change in the two periods. And the transition depends on the changes of the Yangtze riverine sediment supply and the water/sand/biology environment. After emerging gradually from water surface since 1980s, Jiuduansha wetland provides a wider and more suitable habitat for many animals and vegetations, and has more and more biological activities. So, the sedimentation speed of above 0 meter of Jiuduansha wetland is much higher than the lower＇s in the period from 1987 to 2001. After the end of 1990s, because of the influence of the Three Gorges dam and other water conservancy projects, the Yangtze riverine sediment supply decreases remarkably, as a result that the sedimentation speeds of under 0 meter slow down significantly, even the sedimentation speed of the -6 meter contour becomes negative in the period from 2001 to 2004. On the other hand, because of the artificial interferes on Jiuduansha wetland, such as manual planting, nature reserve management, deep-water channel project at north passage, and so on, the sedimentation speeds of 0 meter and the above do not slow down with the decreasing of riverine sediment supply, by contraries, still keep accelerating. So, for the sake of the sustainable development and utilization of Jiuduansha wetland, we must concern the erosion threat resulting from the remarkable decline of riverine sediment supply, and maintain the effectively promoting sedimentation projects, strengthen the protection of nature resources, such as sediments, animals, vegetations and so on.