EAARL Coastal Topography--North Shore, Lake Pontchartrain, Louisiana, 2010

A digital elevation model (DEM) of a portion of the north shore of Lake Pontchartrain, Louisiana, was produced from remotely sensed, geographically referenced elevation measurements by the U.S. Geological Survey (USGS). Elevation measurements were collected over the area on February 28, March 1, and March 5, 2010, using the 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, resulting in a laser swath of approximately 240 meters with an average point spacing of 2-3 meters. The EAARL, developed originally by the National Aeronautics and Space Administration (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 resultant elevation maps for an area are analyzed, they provide a useful tool to make management decisions regarding land development. The data provided represent the last return pulses and were processed and filtered for bare-earth topography. However, in low-lying and emerging vegetation environments, bare-earth topography is not necessarily discernible from the last-return pulses. The difference in water levels between data collections on February 28, March 1, and March 5 resulted in elevation variations in the merged data.美国地质调查局（U.S. Geological Survey, USGS）依托遥感地理参考高程测量数据，制作了美国路易斯安那州庞恰特雷恩湖北岸部分区域的数字高程模型（digital elevation model, DEM）。该数据集的高程测量数据采集于2010年2月28日、3月1日及3月5日，采用实验性先进机载研究激光雷达（Experimental Advanced Airborne Research Lidar, EAARL）完成。EAARL是一款搭载于航空器的脉冲激光测距系统，可同步获取地面高程、植被冠层及海岸地形数据。该系统通过航空器机身底部的开口向地球表面发射高频激光束，并记录激光束发射时刻与机载平台接收反射激光信号的时间差。航空器以约300米的飞行高度、50米每秒的巡航速度飞越目标区域，由此形成约240米宽的激光扫描条带，平均点间距为2至3米。EAARL最初由美国国家航空航天局（National Aeronautics and Space Administration, NASA）位于弗吉尼亚州的沃洛普斯飞行设施研发，其地面高程测量的垂直分辨率可达±15厘米。当采样率达到3千赫兹及以上时，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公里海岸线的测绘工作。对该区域生成的高程地图进行分析后，可作为土地开发管理决策的实用辅助工具。本次提供的数据为最后回波脉冲数据，并经过裸地地形处理与滤波。但在低洼区域与新生植被环境中，仅通过最后回波脉冲未必能准确分辨裸地地形。2010年2月28日、3月1日及3月5日三次数据采集期间的水位差异，会导致合并后的数据集出现高程偏差。