EAARL Submarine Topography-Florida Keys National Marine Sanctuary

Lidar is a remote sensing technique that uses laser light to detect, range, or identify remote objects based on light reflected by the object or emitted through its subsequent fluorescence. Airborne ranging Lidar is now being applied in coastal environments to produce accurate, cost-efficient elevation datasets with high spatial density. The USGS in cooperation with NASA, NOAA, and NPS is using airborne Lidar to measure the submerged topography of the northern Florida reef tract; secondarily, the data will be assessed for its potential in terms of benthic characterization. Elevation measurements were collected over part of the Florida Keys National Marine Sanctuary (FKNMS) using the NASA Experimental Advanced Airborne Research Lidar (EAARL), a pulsed laser ranging system mounted onboard an aircraft to measure subaerial and submarine topography. The system uses a high frequency laser beam 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 EAARL system, developed by the NASA Wallops Flight Facility (WFF) in Virginia, measures ground elevation with a vertical resolution of roughly 15 centimeters. A sampling rate of up to 3 kHz results in an extremely dense spatial elevation data set. The EAARL system is typically flown at 300 m altitude AGL, resulting in a 240 m swath for each flightline. Data collection occurred with approximately 50% overlap between flightlines, resulting in about one laser sounding per square meter. The data were processed by the USGS FISC (St. Petersburg office) to produce 1 meter resolution raster images that can be easily ingested into a Geographic Information System (GIS). The data were organized as 2 km by 2 km data tiles in 32 bit floating-point integer GeoTIFF format.

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 .

激光雷达（Lidar）是一种遥感技术，通过激光照射目标物体，利用目标反射的光线或其后续产生的荧光来探测、测距或识别远距离物体。当前，机载测距激光雷达已应用于海岸环境，可生成空间密度高、精度优异且成本可控的高程数据集。
美国地质调查局（USGS）联合美国国家航空航天局（NASA）、美国国家海洋和大气管理局（NOAA）以及美国国家公园管理局（NPS），正利用机载激光雷达测绘佛罗里达北部礁滩的水下地形；此外，还将评估该数据在底质特征识别方面的应用潜力。
研究团队借助搭载于飞机的实验型先进机载研究激光雷达（EAARL），在佛罗里达群岛国家海洋保护区（FKNMS）的部分区域采集了高程数据。该系统属于脉冲激光测距系统，可同步测量陆上与水下地形。
该系统通过飞机机身底部的开口，向地表发射高频激光束。
激光系统会记录激光束发射时刻与机载平台接收反射信号时刻之间的时间差。
EAARL系统由美国弗吉尼亚州沃洛普斯飞行中心（WFF）研发，其垂直分辨率约为15厘米。
该系统最高采样率可达3千赫兹（kHz），可生成密度极高的空间高程数据集。
EAARL系统通常以距地面300米的高度飞行，每条飞行航线可覆盖240米宽的测绘条带。
数据采集时，飞行航线间设置约50%的重叠度，最终可实现每平方米约一次激光测深的数据密度。
美国地质调查局圣彼得堡分部数据中心（FISC）对采集数据进行了后处理，生成分辨率为1米的栅格影像，可轻松导入地理信息系统（GIS）进行后续应用。
数据以2千米×2千米的分块形式存储，采用32位浮点整型GeoTIFF格式。
如需了解更多激光雷达科学、实验型先进机载研究激光雷达（EAARL）系统及相关测绘项目的详细信息，可访问以下链接：http://ngom.usgs.gov/dsp/overview/index.php 与 http://ngom.usgs.gov/dsp/tech/eaarl/index.php。