EAARL Topography-Gulf Islands National Seashore-Florida

Elevation maps (also known as Digital Elevation Models or DEMs) of Gulf Islands National Seashore were produced from remotely-sensed, geographically-referenced elevation measurements in cooperation with NASA and NPS. Point data in ascii text files were interpolated in a GIS to create a grid or digital elevation model (DEM) of each beach surface. Elevation measurements were collected in Florida, Mississippi and Texas, over Gulf Islands National Seashore, using the NASA Experimental Advanced Airborne Research LiDAR (EAARL), a pulsed laser ranging system mounted onboard an aircraft to measure ground elevation and coastal topography. The system uses high frequency laser beams directed at the earth's surface through an opening in the bottom of the aircraft's fuselage. The laser system records the time difference between emission of the laser beam and the reception of the reflected laser signal in the aircraft. The plane travels over the beach at approximately 60 meters per second while surveying from the low-water line to the landward base of the sand dunes. The EAARL, developed by the National Aeronautics and Space Administration (NASA) located at Wallops Flight Facility in Virginia, measures ground elevation with a vertical resolution of 15 centimeters. A sampling rate of 3 kHz or higher results in an extremely dense spatial elevation data set. Over 100 kilometers of coastline can be easily surveyed within a 3- to 4-hour mission time period. The ability to sample large areas rapidly and accurately is especially useful in morphologically dynamic areas such as barrier beaches. Quick assessment of topographic change can be made following storms comparing measurements against baseline data. When subsequent elevation maps for an area are analyzed, they provide a useful tool to make management decisions regarding coastal development.

For more information on Lidar science and the Experimental Advanced Airborne Research Lidar (EAARL) system and surveys, see http://ngom.usgs.gov/dsp/overview/index.php and http://ngom.usgs.gov/dsp/tech/eaarl/index.php .

本数据集涵盖海湾群岛国家海岸（Gulf Islands National Seashore）的高程地图，该类地图又称数字高程模型（Digital Elevation Models，DEM），由美国国家航空航天局（National Aeronautics and Space Administration，NASA）与美国国家公园管理局（National Park Service，NPS）合作，基于遥感获取的地理参考高程测量数据制作完成。研究人员将ASCII文本文件（American Standard Code for Information Interchange，ASCII）中的点数据通过地理信息系统（Geographic Information System，GIS）进行插值处理，生成各海滩表面的网格型数字高程模型。

本次高程测量作业覆盖佛罗里达州、密西西比州与得克萨斯州境内的海湾群岛国家海岸区域，采用了NASA实验性先进机载研究激光雷达（Experimental Advanced Airborne Research LiDAR，EAARL）——一款搭载于航空器的脉冲激光测距系统，用于获取地面高程与海岸地形数据。该系统通过航空器机身底部的开口，将高频激光束投射至地球表面；激光系统会记录激光束发射与机载接收反射激光信号之间的时间差。航空器以约60米每秒的速度沿海滩飞行，测绘范围覆盖从低潮线至沙丘向陆一侧基底的区域。

EAARL由位于弗吉尼亚州沃洛普斯飞行设施的美国国家航空航天局研发，其地面高程测量的垂直分辨率可达15厘米。当采样率达到3千赫兹（kHz）及以上时，可生成密度极高的空间高程数据集。单次任务时长3至4小时即可轻松完成超过100公里海岸线的测绘作业。

快速且精准地采集大面积数据的能力，在障壁海滩这类地貌动态变化显著的区域尤为实用。风暴过后，通过将实测数据与基线数据对比，可快速评估区域地形变化情况。对某一区域后续生成的高程地图进行分析后，可为沿海开发相关的管理决策提供有效支撑依据。

如需了解更多激光雷达（Light Detection and Ranging，LiDAR）科学、实验性先进机载研究激光雷达（EAARL）系统及相关测绘的详细信息，请访问以下网址：http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。