Abstract Insights into the dynamics of coastlines and tidal flats at fine spatial and temporal resolutions are essential for sustainable development. Previous studies were generally conducted at relatively coarse temporal intervals, which hardly captured detailed coastal dynamics, especially in rapidly developing islands. In this study, we developed a new method to map the monthly changes in coastlines and tidal flats in the Zhoushan Archipelago during 1985–2017 using the full time series of Landsat images based on the Google Earth Engine (GEE) platform. First, we built the full time series of the Modified Normalized Difference Water Index (MNDWI). Second, we derived temporal segments of MNDWI using a binary segmentation algorithm. Third, we classified the corresponding coastal cover types (i.e., water, tidal flats, and land) for each temporal segment based on the features of MNDWI and regional tidal heights. Finally, we identified the change information including conversion types, and turning years and months. Results indicate that the proposed method can well identify turning years with an overall accuracy of 90% and map coastal cover types with overall accuracies of 89–94% in 1985 and 87–92% in 2017. Significant coastline expansions and declines in tidal flats were found in the study area. The areas of water and tidal flats decreased by 6% and 10% during 1985–2017, respectively, while the land area increased by 18%. The land reclamation was accelerated in the recent decade, and mainly occurred on the medium-large islands, their surrounding small islands, and the islands close to the mainland. The proposed framework based on the GEE platform is transferable to investigate coastal dynamics in other areas. The derived information of changes in coastlines and tidal flats is of great use for sustainable management and ecological studies in coastal areas.

中文翻译：

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使用 Landsat 图像的全时间序列绘制发展中岛屿海岸线和潮滩的变化

摘要 以精细的空间和时间分辨率洞察海岸线和潮滩的动态对于可持续发展至关重要。以前的研究通常是在相对粗略的时间间隔内进行的，很难捕捉到详细的海岸动态，尤其是在快速发展的岛屿中。在这项研究中，我们开发了一种新的方法来绘制 1985-2017 年舟山群岛海岸线和滩涂的月变化，使用基于谷歌地球引擎 (GEE) 平台的全时间序列 Landsat 图像。首先，我们构建了修正归一化差异水指数 (MNDWI) 的全时间序列。其次，我们使用二进制分割算法导出了 MNDWI 的时间段。第三，我们对相应的海岸覆盖类型（即水域、滩涂、和土地）基于 MNDWI 和区域潮汐高度的特征的每个时间段。最后，我们确定了更改信息，包括转换类型、转换年份和月份。结果表明，该方法能够很好地识别转折年，总体准确率为90%，绘制海岸覆盖类型图，总体准确率为1985年89-94%和2017年87-92%。研究区内发现。1985-2017年间，水域面积和滩涂面积分别减少了6%和10%，陆地面积增加了18%。近十年来，土地开垦步伐加快，主要集中在中大岛及其周边小岛和靠近大陆的岛屿上。基于 GEE 平台的拟议框架可用于调查其他地区的沿海动态。海岸线和滩涂变化的衍生信息对于沿海地区的可持续管理和生态研究非常有用。