EAARL Bare Earth Topography-Fire Island National Seashore

A bare earth elevation map (also known as a Digital Elevation Model or DEM) of Fire Island National Seashore was produced from remotely-sensed, geographically-referenced elevation measurements in cooperation with the U.S. Geological Survey (USGS), National Air and Space Administration (NASA), and the National Park Service (NPS). 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 m. 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 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. 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 .火岛国家海岸（Fire Island National Seashore）的裸地高程图（亦称为数字高程模型，Digital Elevation Model，缩写DEM）由美国地质调查局（U.S. Geological Survey，USGS）、美国国家航空航天局（National Air and Space Administration，NASA）及美国国家公园管理局（National Park Service，NPS）合作，基于遥感地理参考高程测量数据制作而成。该区域的高程数据通过NASA实验型先进机载研究激光雷达（Experimental Advanced Airborne Research Lidar，EAARL）采集，该系统为安装于航空器上的脉冲激光测距系统，可用于测量地面高程、植被冠层及海岸地形。系统通过航空器机身底部的开孔将高频激光束投射至地球表面，并记录激光束发射时刻与航空器接收反射激光信号时刻之间的时间差。作业飞机以约300米的飞行高度、约50米每秒的速度飞越目标区域。由NASA在弗吉尼亚州沃洛普斯飞行设施开发的EAARL，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，可生成空间密度极高的高程数据集。在3至4小时的任务时长内，即可轻松完成超过100公里海岸线的测绘工作。对某一区域的后续高程图进行分析后，可作为土地开发相关管理决策的实用工具。 如需了解更多激光雷达科学、实验型先进机载研究激光雷达系统及相关测绘的信息，请访问：http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。