EAARL-B Topography-Big Thicket National Preserve: Big Sandy Creek Corridor Unit, Texas, 2014

A first-surface topography Digital Elevation Model (DEM) mosaic for the Big Sandy Creek Corridor Unit of Big Thicket National Preserve in Texas was produced from remotely sensed, geographically referenced elevation measurements collected on January 19, 21, 22, 29, and 30, 2014 by the U.S. Geological Survey, in cooperation with the National Park Service - Gulf Coast Network. Elevation measurements were collected over the area using the second-generation Experimental Advanced Airborne Research Lidar (EAARL-B), 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 55 meters per second at an elevation of approximately 300 meters, resulting in a laser swath of approximately 240 meters with an average point density of 1.4 points per square meter. A peak sampling rate of 15-30 kilohertz results in an extremely dense spatial elevation dataset. More than 100 kilometers of coastline can be surveyed easily within a 3- to 4-hour mission. When resultant elevation maps for an area are analyzed, they provide a useful tool to make management decisions regarding land development.

针对德克萨斯州大密林国家保护区（Big Thicket National Preserve）大桑迪溪走廊单元的地表首反射型数字高程模型（Digital Elevation Model, DEM）镶嵌数据集，由美国地质调查局（U.S. Geological Survey）联合国家公园服务局墨西哥湾沿岸网络（National Park Service - Gulf Coast Network），基于2014年1月19、21、22、29及30日采集的遥感地理参考高程测量数据制作完成。

采集该区域高程数据所用的设备为第二代实验先进机载研究激光雷达（Experimental Advanced Airborne Research Lidar, EAARL-B），这是一款搭载于航空器的脉冲激光测距系统，可同步测量地面高程、植被冠层及海岸地形。该系统通过飞机机身底部的开口向地球表面投射高频激光束，并记录激光束发射时刻与机载平台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、55米/秒的速度飞越目标区域，由此形成的激光扫描带宽度约为240米，平均点密度达每平方米1.4个点。该系统峰值采样率为15-30千赫兹，可生成密度极高的空间高程数据集；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。

对某一区域生成的高程地图开展分析后，可作为土地开发相关管理决策的实用辅助工具。