EAARL Coastal Topography-St. John, U.S. Virgin Islands 2003: First Surface

A first surface elevation map (also known as a Digital Elevation Model, or DEM) of a portion of St. John, U.S. Virgin Islands was produced from remotely sensed, geographically referenced elevation measurements cooperatively by the U.S. Geological Survey (USGS), National Aeronautics and Space Administration (NASA), and 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 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）、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）联合基于遥感地理参考高程测量数据，制作了美属维尔京群岛圣约翰岛部分区域的首张地表高程图（亦称为数字高程模型，Digital Elevation Model, DEM）。本次高程测量采用NASA研发的实验型先进机载研究激光雷达（Experimental Advanced Airborne Research Lidar, EAARL）完成，该系统为搭载于航空器的脉冲激光测距装置，可同步测量地面高程、植被冠层及海岸地形。系统通过飞机机身底部的开口向地球表面发射高频激光束，并记录激光束发射与机载接收反射激光信号之间的时间差，以此获取高程数据。该航空器以约每秒50米的速度、约300米的飞行高度在目标区域上空巡航。由NASA弗吉尼亚州沃洛普斯飞行设施研发的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3千赫兹及以上时，可生成极为密集的空间高程数据集。单次3至4小时的飞行任务即可轻松完成超过100公里海岸线的测绘作业。当对某一区域的后续高程图进行分析时，此类数据可作为土地开发管理决策的实用辅助工具。
如需了解更多关于激光雷达科学、实验型先进机载研究激光雷达（EAARL）系统及测绘工作的相关信息，请访问http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。