Assateague Island Back-Island Shorelines Extracted from orthoimagery, 1989 • 2013

Assessing the physical change to shorelines and wetlands is critical in determining the resiliency of wetland systems that protect adjacent habitat and communities. The wetland and back-barrier shorelines of Assateague Island, located in Maryland and Virginia, changed as a result of wave action and storm surge that occurred during Hurricane Sandy, which made landfall on October 29, 2012. The impact of Hurricane Sandy will be assessed and placed in its historical context to understand the future vulnerability of wetland systems.
Making these assessments will rely on data extracted from current and historical resources such as maps, aerial photographs, satellite imagery, and lidar elevation data, which document physical changes over time.
This USGS Data Series publication includes several open-ocean shorelines, back-island shorelines, back-island shoreline points, sand area polygons, and sand lines for Assateague Island that were extracted from orthoimagery (orthoaerial photography) dated from April 12, 1989 to September 5, 2013.
This data set consists of lines that were digitized at the intersection of the back-island shoreline and a set of transects spaced at 20-meter (m) intervals. The transects, asis_transects_ln_20m_utm18.shp, are included in this Data Series publication and can be accessed via the Data Download page. The lines falling between the transects do not follow the natural back-island shoreline. Only one back-island shoreline/transect intersection line vector was digitized per transect.
Orthoimagery of Assateague Island were acquired in digital format from U.S. Department of Agriculture (USDA), U.S. Geological Survey (USGS) and Virginia Geographic Information Network (VGIN) courtesy of the Commonwealth of Virginia.
The following list provides additional details about the orthoimagery used. The digitized back-island shorelines for all dates have been compiled into one data set (shapefile) named asis_bshrln_1989_2013_guided.shp. The orthoimage date for each line is included in the shapefile attribute table Date_ field.

Date State Type Source Resolution

198904129(1) MD DOQQ USGS 1 meter (m)
19940320 VA DOQQ USGS 1 m
20041105 VA NAIP USDA 2 m
20050608 VA NAIP USDA 2 m
20050615 MD NAIP USDA 1 m
20060528 VA NAIP USDA 2 m
20060701 MD NAIP USDA 2 m
20070622 MD NAIP USDA 1 m
20080525 VA NAIP USDA 1 m
20090626 MD NAIP USDA 1 m
20090726 VA NAIP USDA 1 m
20090807 VA NAIP USDA 1 m
20110530 VA NAIP USDA 1 m
20110602 MD NAIP USDA 1 m
20120512 VA NAIP USDA 1 m
20130315 VA VBMP VGIN(2) 1 m(3)
20130905 MD NAIP USDA 1 m

DOQQ Digital Orthophoto Quarter Quads
NAIP National Agriculture Imagery Program
VBMP Virginia Base Mapping Program

(1)Color Infrared orthoimagery; all others are natural color.
(2)Imagery courtesy of the Commonwealth of Virginia.
(3)Resampled from 1-foot resolution imagery.

评估海岸线与湿地的物理变化，是明确湿地系统恢复力的核心环节——湿地系统可保护邻近的生境与社区。位于马里兰州与弗吉尼亚州的阿萨蒂格岛（Assateague Island）的湿地及后障海岸（back-barrier shorelines），因2012年10月29日登陆的桑迪飓风（Hurricane Sandy）引发的波浪作用与风暴潮发生了显著变化。本研究将评估桑迪飓风造成的影响，并结合历史背景展开分析，以明晰湿地系统未来的脆弱性。
此类评估将依托从现有及历史资源中提取的数据开展，这些资源包括记录了长期物理变化的地图、航空摄影照片、卫星影像与激光雷达（lidar）高程数据。
本美国地质调查局（U.S. Geological Survey, USGS）数据系列出版物包含阿萨蒂格岛的多组空间数据：开阔洋面海岸线、岛后海岸线、岛后海岸线点、沙区多边形与沙线，所有数据均提取自1989年4月12日至2013年9月5日期间的正射影像（orthoimagery，即正射航空摄影）。
本数据集由在岛后海岸线与间隔20米（m）布设的一系列断面的交点处数字化得到的线条构成。这些断面文件为asis_transects_ln_20m_utm18.shp，已包含在本数据系列出版物中，可通过数据下载页面获取。断面之间的线条并未贴合自然岛后海岸线，且每个断面仅数字化了一条岛后海岸线/断面交线矢量文件。
阿萨蒂格岛的正射影像以数字格式从美国农业部（U.S. Department of Agriculture, USDA）、美国地质调查局（USGS）以及弗吉尼亚地理信息网络（Virginia Geographic Information Network, VGIN）获取，谨此感谢弗吉尼亚州联邦政府的授权提供。
以下列表详细说明了所用正射影像的相关信息。所有日期的数字化岛后海岸线已整合至一个名为asis_bshrln_1989_2013_guided.shp的形状文件（shapefile）数据集中。每条线条对应的正射影像日期已包含在该形状文件的属性表Date_字段中。
日期 州 类型 来源 分辨率
198904129(1) MD DOQQ USGS 1米（m）
19940320 VA DOQQ USGS 1 m
20041105 VA NAIP USDA 2 m
20050608 VA NAIP USDA 2 m
20050615 MD NAIP USDA 1 m
20060528 VA NAIP USDA 2 m
20060701 MD NAIP USDA 2 m
20070622 MD NAIP USDA 1 m
20080525 VA NAIP USDA 1 m
20090626 MD NAIP USDA 1 m
20090726 VA NAIP USDA 1 m
20090807 VA NAIP USDA 1 m
20110530 VA NAIP USDA 1 m
20110602 MD NAIP USDA 1 m
20120512 VA NAIP USDA 1 m
20130315 VA VBMP VGIN(2) 1 m(3)
20130905 MD NAIP USDA 1 m
DOQQ 数字正射影像四分之一象限图（Digital Orthophoto Quarter Quads）
NAIP 国家农业影像计划（National Agriculture Imagery Program）
VBMP 弗吉尼亚基础制图计划（Virginia Base Mapping Program）
(1) 该影像为彩色红外正射影像；其余均为自然色影像。
(2) 本影像由弗吉尼亚州联邦政府提供。
(3) 该数据从1英尺分辨率的影像重采样而来。