EAARL Topography-Cape Cod National Seashore

Elevation maps (also known as Digital Elevation Models or DEMs) of Cape Cod 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 Massachusetts, over Cape Cod 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 .

科德角国家海岸（Cape Cod National Seashore）的高程地图（亦称为数字高程模型，Digital Elevation Model，简称DEM），系依托遥感获取的地理参考高程测量数据，联合美国国家航空航天局（National Aeronautics and Space Administration，简称NASA）与美国国家公园管理局（National Park Service，简称NPS）共同制作完成。研究人员将ASCII文本文件中的点数据通过地理信息系统（Geographic Information System，简称GIS）进行插值处理，以此生成各海滩表面的网格型数字高程模型。本次高程数据采集工作在美国马萨诸塞州的科德角国家海岸区域开展，所用设备为NASA实验型先进机载研究激光雷达（Light Detection and Ranging，简称LiDAR）系统（Experimental Advanced Airborne Research LiDAR，简称EAARL）——该系统是一款搭载于航空器的脉冲激光测距装置，用于测量地面高程与海岸地形。系统通过航空器机身底部的开口，将高频激光束投射至地球表面，并记录激光束发射时刻与机载接收反射激光信号时刻之间的时间差。作业时，航空器以约60米/秒的速度飞越海滩，测绘范围从低潮线一直延伸至沙丘向陆侧的基底。EAARL系统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。当采样率达到3千赫兹（kHz）及以上时，可生成密度极高的空间高程数据集。单次任务耗时3至4小时，即可轻松完成超过100公里海岸线的测绘工作。这种快速且精准的大面积采样能力，在障壁海滩这类地貌动态变化剧烈的区域尤为实用。在风暴过后，研究人员可将实测数据与基准数据进行比对，快速评估地形变化情况。通过对某一区域后续生成的高程地图进行分析，可为海岸开发相关的管理决策提供有力支撑。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）系统及相关测绘作业的信息，请访问：http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。