基于最大值合成和最大类间方差法莱州湾滨海滩涂变化研究

A study on the changes in coastal tidal flats in the Laizhou Bay based on MSIC and OTSU

滨海滩涂是一种重要的滨海湿地类型,在维护生物多样性、影响全球气候和环境变化等方面具有重要的生态价值。由于滨海滩涂只在最低潮时期短暂全部呈现,先前的遥感解译结果中,滩涂信息存在明显的漏分和误分现象。基于Google Earth Engine(GEE)平台和Landsat系列卫星数据,构建1990年、2000年、2010年和2020年4个时间段的高质量密集时间序列影像堆栈,结合最大光谱指数合成算法(maximum spectral index composite,MSIC)和最大类间方差算法(Otsu algorithm,OTSU),对我国莱州湾滨海滩涂资源进行快速、自动提取。基于面向对象分析技术和模糊逻辑分析方法(fuzzy-based segmentation parameter,FbSP)最优尺度对滨海滩涂周边土地覆被进行解译,分析滨海滩涂的时空演变规律。结果表明:1990—2020年间莱州湾滨海滩涂呈现持续减少的趋势,2020年莱州湾滨海滩涂面积为822.38 km^(2),相较于1990年减少了约40%,其中,2000—2010年缩减幅度最大,为304.78 km^(2);除黄河口区域滨海滩涂向海迁移,莱州湾其他区域的滨海滩涂斑块整体呈向陆迁移趋势;人类活动是近30 a间莱州湾滩涂变化的主导因素,其中,养殖池/盐田的扩张直接侵占了414.20 km^(2)的滨海滩涂。

Coastal tidal flats,as a major type of coastal wetlands,have significant ecological value in maintaining biodiversity and influencing global climate and environmental change.Since they are only exposed in their entirety at the lowest tide,the previous remote sensing interpretation results showed significant omissions and misclassifications of the tidal flats.Based on the Google Earth Engine(GEE)platform and the Landsat series satellite data,this study constructed high-quality dense time series image stacks for four time periods,i.e.,1990,2000,2010,and 2020.Then,these image stacks were combined with the maximum spectral index composite(MSIC)algorithm and the Otsu algorithm(OTSU)for rapid and automatic extraction of coastal tidal flats resources in Laizhou Bay of China.Furthermore,the land cover around the coastal tidal flats was delineated based on the object-oriented analysis technology and the fuzzy-based segmentation parameter(FbSP)optimal scale.Finally,the spatial and temporal evolution patterns of the coastal tidal flats were analyzed.The results are shown as follows.During 1990—2020,the coastal tidal flats in Laizhou Bay gradually decreased,with an area of 822.38 km^(2) in 2020,a reduction of about 40% compared with that in 1990.The largest reduction was 304.78 km^(2) during 2000—2010.The coastal tidal flats near the Yellow River estuary showed a seaward migration,while the coast tidal flat patches in other regions of Laizhou Bay showed a landward migration.Human activities were the dominant factors in the changes in tidal flats in Laizhou Bay in the past 30 years.Among them,the expansion of aquaculture ponds/salt fields directly encroached on 414.20 km^(2) of coastal tidal flats.