Baseline_OpenOcean.shp - Baseline Along the Open-Ocean (South-Facing) Coast of Dauphin Island, Alabama, Generated to Calculate Shoreline Change Rates.

Analysis of shoreline change for Dauphin Island, Alabama was conducted using the U.S. Geological Survey (USGS) Digital Shoreline Analysis System (DSAS) v.4.3 for ArcMap (Thieler and others, 2009) and vector shorelines derived from air photos and lidar elevation surveys. DSAS-generated transects were cast at 100-meter intervals along a user defined shore-parallel baseline. The intersections of transects with the mean high water (MHW) shoreline positions are identified by intercept points. The rate of shoreline change was determined by measuring the differences in the distance to each historical shoreline position from the baseline along each transect. Three analyses of change rates were conducted using a combination of shorelines derived from different data sources. Shoreline change rates from the wet dry line (WDL) shoreline were derived from 10 sets of air photos from 1940 - 2015. Rates of change were also calculated using MHW shorelines extracted from 14 lidar datasets from 1998 - 2014. A final change analysis was conducted using a combination of all WDL (aerial) and MHW (lidar) shorelines, from 1940 - 2015.本研究针对美国阿拉巴马州多芬岛的岸线变化开展分析，采用美国地质调查局（U.S. Geological Survey, USGS）面向ArcMap开发的数字岸线分析系统（Digital Shoreline Analysis System, DSAS）v4.3（Thieler等，2009），以及源自航空照片与激光雷达高程测量的矢量岸线数据。DSAS生成的岸线断面以100米间隔沿用户自定义的岸线平行基线布设，断面与平均高潮位（mean high water, MHW）岸线位置的交点通过截点进行标记。岸线变化速率通过测算每条断面上基线至各历史岸线位置的距离差值予以确定。 本研究基于不同数据源获取的岸线组合，共开展三组变化速率分析：其一，基于干湿线（wet dry line, WDL）岸线的变化速率，源自1940年至2015年间的10组航空照片数据；其二，利用1998年至2014年间14组激光雷达数据集提取的MHW岸线，计算得到岸线变化速率；其三，基于1940年至2015年间全部WDL（航空）与MHW（激光雷达）岸线的组合数据，开展最终的变化分析。