EAARL Coastal Topography and Imagery--Naval Live Oaks Area, Gulf Islands National Seashore, Florida, 2007

A digital elevation map (also known as a Digital Elevation Model, or DEM) of the Naval Live Oaks Area in Florida's Gulf Islands National Seashore was produced from remotely sensed, geographically referenced elevation measurements cooperatively by the U.S. Geological Survey (USGS), the National Park Service (NPS), and the National Aeronautics and Space Administration (NASA). Elevation measurements were collected over the area using the NASA Experimental Advanced Airborne Research Lidar (EAARL), a pulsed laser ranging system mounted onboard an aircraft to measure ground elevation, vegetation canopy, 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 target area at approximately 50 meters per second at an elevation of approximately 300 meters. The EAARL, developed by NASA at Wallops Flight Facility in Virginia, measures ground elevation with a vertical resolution of +/-15 centimeters. A sampling rate of 3 kilohertz or higher results in an extremely dense spatial elevation dataset. Over 100 kilometers of coastline can be surveyed easily within a 3- to 4-hour mission. When subsequent elevation maps for an area are analyzed, they provide a useful tool to make management decisions regarding land 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 .美国地质调查局（U.S. Geological Survey, USGS）、国家公园管理局（National Park Service, NPS）与美国国家航空航天局（National Aeronautics and Space Administration, NASA）合作，基于遥感地理参考高程测量数据，制作了佛罗里达州墨西哥湾群岛国家海岸海军活橡林区的数字高程图（Digital Elevation Model, DEM，又称数字高程模型）。高程数据采集工作依托美国国家航空航天局的实验先进机载研究激光雷达（Experimental Advanced Airborne Research Lidar, EAARL）开展——该系统为搭载于飞机的脉冲激光测距系统，可同步测量地面高程、植被冠层与海岸地形。系统通过飞机机身底部的开口向地表发射高频激光束，并记录激光束发射与机载接收反射信号之间的时间差，以此计算高程信息。作业时，飞机以约300米的飞行高度、每秒约50米的速度飞越目标区域。由美国国家航空航天局弗吉尼亚州沃洛普斯飞行设施研发的EAARL，其地面高程测量垂直分辨率可达±15厘米。当采样率达到3千赫兹及以上时，可生成密度极高的空间高程数据集，一次3至4小时的飞行任务即可轻松完成超100公里海岸线的测绘工作。对某一区域的多期高程图进行分析，可作为土地开发管理决策的有效辅助工具。 如需了解更多激光雷达（Lidar）科学、实验先进机载研究激光雷达系统及测绘项目的相关信息，请访问：http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。