基于分形维数的环渤海地区海岸线变迁及成因分析

利用遥感和GIS技术提取了环渤海地区1980年、1990年、2000年和2010年4期海岸线信息,采用网格法计算每期海岸线的分形维数;分析了海岸线及其分形维数的时空变化特征、并探讨了其与海岸开发活动之间的关系。研究表明:在1980—2010年间,研究区海岸线长度持续增加,变化强度逐渐增大,海岸线共增加了1 074.35 km;从时间过程看,2000年以后海岸线长度进入快速增长时期;从区域范围看,以天津市和河北省所在的渤海湾地区海岸线的变迁最显著。研究期间,环渤海地区海岸线整体向海推进,海岸线分形维数逐渐增大,岸线形状趋于复杂。人为的海岸开发活动是海岸线变迁的主导因素,2000年之前海岸开发以围垦养殖、盐田为主;之后,港口码头建设和城镇建设型的海岸工程逐渐增多。海岸线的分形维数与海岸带的物质组成与演变过程有直接关系,大量规模不等的海岸工程的建设是海岸线分形维数变化的主导因素。

Spatial-temporal variations of coastlines in Bohai Rim based on fractal dimension and their causes analysis

The coastline information of Bohai Rim in the year of 1980, 1990, 2000 and 2010 was extracted using remote sensing images of Landsat MSS, TM and ETM+ and GIS techniques, and the fractal dimension of the coastline was calculated by box-counting method. The characteristics of spatial-temporal variations of the coastline's length and the driving forces of coastline changes were assessed, and the relationship between the coastal development activities on various scales and fractal dimension changes were also discussed. The results showed that during the research period, the coastline length of the study area increased by 1 074.35 km and the rising intensity increased progressively. The coastline length entered a period of rapid growth after 2000. The most significant change of coastline length was found in Bohai Bay. During the study period, the coastline mainly expanded to the sea. Human development activities were the leading factor for coast change. Before 2000, coastal development was predominantly constituted by reclamation of aquaculture and salt fields; while after 2000, factors causing coastal change tended to become diversified and rates of harbor construction and construction lands increased. The fractal dimension of the overall coastline was increased steadily, indicating that the geometry of the coastline of the study area became more complex. The magnitude and variations of fractal dimension were directly related to material composition and evolution process in the coastal zone. A large numbers of coastal engineering construction of various scales were the leading factor in fractal dimension variation.