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 .

墨西哥湾群岛国家海岸的高程地图（Digital Elevation Models，简称DEM）系通过遥感地理参考高程测量数据制作而成，合作方包括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）。研究人员将美国信息交换标准代码（American Standard Code for Information Interchange，ASCII）文本文件中的点数据在地理信息系统（Geographic Information System，GIS）中进行插值处理，以生成各海滩表面的栅格化数字高程模型（DEM）。

本次高程测量作业依托NASA实验先进机载研究激光雷达（Light Detection and Ranging，LiDAR，简称EAARL）开展，该系统是搭载于飞机上的脉冲激光测距系统，用于测量地面高程与海岸地形。该系统通过飞机机身底部的开口将高频激光束射向地球表面，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。作业时，飞机以约60米每秒的速度飞越海滩，测量范围覆盖从低潮线至沙丘向陆侧基部的区域。

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（NASA）研发，其地面高程测量的垂直分辨率可达15厘米。3千赫兹（kHz）及更高的采样率可生成极为密集的空间高程数据集。单次任务时长3至4小时内，即可轻松完成超过100公里海岸线的测量作业。快速且精准地对大面积区域进行采样的能力，在障壁海滩这类地貌动态变化显著的区域尤为实用。在风暴过后，可将实测数据与基准数据对比，快速评估地形变化情况。对某一区域后续生成的高程地图进行分析后，可将其作为制定沿海开发管理决策的实用工具。

如需了解更多关于激光雷达科学、实验先进机载研究激光雷达（EAARL）系统及测量作业的相关信息，请访问：http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。