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About LIDAR Key Features:
Applications:
Airborne Laser Topographic Mapping (ALTM) Technology is a subset of an active remote sensing technology known as LIDAR (acronym for Light Detection And Ranging). LIDAR systems direct pulses of laser light toward the ground and detect the return times of reflected or back-scattered pulses in order to determine ranges to a reflecting surface. This technology has been used for many years in ground based surveying instruments known as Total Stations or Electronic Distance Measurement (EDM) and in military applications. The use of LIDAR for airborne topographic mapping began in the late 1970's, but early systems suffered because of poor determination in the aircraft position and orientation. By early 1990, advances in navigation technology, electronic miniaturization and laser technology lead to the development of practical ALTM systems. Most modern ALTM systems consist of three basic components: the laser scanner, a kinematic Global Position System (GPS), and the Inertial Measurement Unit (IMU). The laser scanner detects the range from aircraft to ground by recording the time difference between laser pulses sent out and reflected back. In addition, many systems allow the recording of multiple returns and the return intensity for each laser pulse. Pulse repetition rates of commercial ALTM systems range between 10 and 100 kHz. A rotating or oscillating mirror mounted in front of the laser causes the laser to scan back and forth, allowing the coverage of a wide swath beneath the flight path. This oscillation of the scanner mirror, in combination with forward motion of the aircraft, typically results in a zigzag scan pattern beneath the flight path. A GPS receiver mounted in the aircraft records aircraft positions continuously. A second GPS station situated at a known ground position provides differential corrections for more accurate estimation of the aircraft trajectory. After the flight, a precise aircraft trajectory is determined by post processing the aircraft and ground station GPS carrier phase data. Aircraft orientation is measured by the IMU. The IMU consists of a set of gyroscopes and accelerometers that continuously measure the roll, pitch, heading and acceleration of the aircraft many times per second. After the flight, the aircraft trajectory is then combined with the laser range data, scanner mirror angle, and the IMU measurements to determine the precise horizontal coordinates and vertical elevations of each laser reflection.
LIDAR at IHRC The Florida International University (FIU) International Hurricane Research Center (IHRC) and the University of Florida (UF) Geomatics program purchased an Optech model 1233 ALTM system, at a cost exceeding one million dollars. The system is mounted in a Cessna 337 twin-engine light aircraft owned jointly by FIU and UF. The Optech 1233 ALTM utilizes a 33 kHz, pulsed laser range finder (LIDAR) which returns vertical ranges to the ground on a swath beneath the flight path. When combined with advanced inertial navigation and kinematic GPS positioning, this system can return absolute elevations of the ground surface accurate to 6 inches (15cm). For a typical aircraft deployment (120 miles per hour ground speed, 3000 foot altitude), we are able to map a 2000-foot-wide, over 500-mile-long swath of ground surface elevations spaced 5 feet apart in just a few hours and at a fraction of the cost of conventional surveying. Since acquiring an airborne laser in 1999, IHRC has surveyed about 2,000 km2 of areas vulnerable to storm surge flooding in South Florida using airborne LIDAR technology as part of the Windstorm Simulation and Modeling Project funded by FEMA through the Florida Department of Community Affairs (FL DCA). Over 1,500 million irregularly spaced ground surface elevations have been collected for these areas. IHRC also collected LIDAR measurements at Martin County (2003), Vero Beach, Florida (2000), the outer coastline of North and South Carolina (2000), and the south shore of Long Island, New York (2002) to study coastal vulnerability and beach erosion. These data collection activities are part of an extensive research effort that has contributed to the development of unique capabilities in LIDAR data filtering, building and tree extraction algorithms, data processing software development, storm surge flood modeling, analysis of freshwater flooding impact, and beach erosion using LIDAR measurements.
Above is a comparison of ALTM data with USGS data in Broward County, Florida. The left figure is a USGS 30 meter DEM and the right figure is an IHC 30 meter DEM produced from ALTM data. Notice the significantly higher resolution in the IHC DEM. In some areas, elevations differences of as much as 3 meters (10 ft.) could result in large errors in flood maps.
Above is a comparison of ALTM data with USGS data in Broward County, Florida. The left figure is a USGS 30 meter DEM and the right figure is an IHC 30 meter DEM produced from ALTM data. Notice the significantly higher resolution in the IHC DEM. In some areas, elevations differences of as much as 3 meters (10 ft.) could result in large errors in flood maps.
Zhang K. and D. Whitman 2004. Comparison of three algorithms for
filtering airborne LIDAR data. Photogrammetric Engineering and
Reomote Sensing, in press. Whitman D., K. Zhang, S.P. Leatherman, and W. Robertson, 2003.
An Airborne Laser Topographic Mapping Application to Hurricane Storm
Surge Hazard. In G. Heiken, R. Fakundiny, and J. Sutter (editors),
Earth Science in the Cities. p. 363-376.
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Miami-Dade
County 3-D Images Rendered from Airborne Laser Data. The image shows
downtown Miami, Florida looking Northwest Biscayne Bay. The data
was collected by an Optech ALTM 1233 topographic mapping system
operated by FIU.