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Lidar Remote Sensing Demonstration Project
Project Leader: Dr. Stephen D. Prince, RESAC, University of MarylandUniversity of Maryland, College ParkBackground
The Regional Earth Sciences Application Center (RESAC) at the University of Maryland joins VAccess - MAGIC as a full partner in its second year of activity. We propose to contribute the first, wide-footprint lidar survey (Blair et al., 1999) of an entire watershed, the Patuxent river, and to develop maps of surface topography with very high accuracy for surface runoff routing, flood prediction and stream mapping, together with maps of vegetation canopy for use in land management and building locations and heights. The project will also serve as a realistic demonstration of the new instrument in an operational mode. In addition, the instrument will be flown from the headwaters of the Potomac River in the Blue Ridge Mountains (NW) to the mouth of the Potomac (SE) at Chesapeake Bay, providing scientific information of another watershed with diverse terrain types (mountains, forests, flood plains, wetlands and urban/suburban growth) for Virginia, an initial step toward the state’s lidar applications development.
This new Lidar technology has been developed by our partners at NASA Goddard Space Flight Center, and has been thoroughly tested in sites throughout the USA (Patuxent River, MD; Sierra Nevada, CA; Hubbard Brook LTER, NH; Coweeta LTER, NC; Duke Forest, NC, USA; La Selva Research Center, Costa Rica; Barro Colorado Island, Panama) by a University of Maryland team, including the Leader of the current project. This Patuxent deployment, however, will be the first using this revolutionary technology to collect data for an entire watershed and to include the built environment as well as vegetation.
North Carolina has recently undertaken an extensive conventional Lidar survey for flood insurance mapping, and Maryland is considering a statewide Lidar survey. The lidar instruments available for commercial contracting, however, all use narrow beam Lidar, which can only reliably measure the first interception, be it the ground or a tree top. The instrument we will use (Laser Vegetation Imaging Sensor, LVIS) can digitize the entire time history of the outgoing and return laser pulses and can measure very precisely the range to the surface as well as the vertical distribution of surfaces within each 5m diameter footprint. Validation studies consistently find better than 1m vertical accuracy.
Figure 4. A flight configuration of the LVIS airborne laser altimeter. A 1-km wide swath is generated using 200 5m wide footprints.
Technical Approach
There is intense interest in the potential of broad-beam lidar data among state and local government, because of its numerous products - far beyond those possible with conventional Lidar, however the instrument has only been used in development and science programs. The planned deployment will provide the opportunity to assess the many products, including subcanopy topography, heights of objects above the surface, the internal detail of forest canopies, and co-occurrences of streams and dense vegetation that are required for effective riparian buffers, for example. Furthermore, the deployment will be for an area of approximately 1,000km2, large enough for government agencies to assess in a realistically large program and large enough for a thorough study of the issues that arise in a deployment under operational conditions. Whereas there is no doubt about the ability of this project to provide the products listed below, this deployment will also furnish the data needed to assess the operational characteristics and commercial potential of the new technology.5 (a) 5 (b)
The Patuxent LVIS mission will involve flying the instrument in a commercial Cessna Conquest for up to 60hrs to cover 1,000km2 of the Upper Patuxent Watershed. The data will be presented as maps of subcanopy topography with approximately 1m or better accuracy and maps of above ground structures (buildings) and information of vegetation canopies (Figs 1, 3, 4). Footprint size will be 5m.
The data will be interpreted and provided to the numerous Federal (e.g., EPA Chesapeake Bay Program), State (e.g., MD Department of Natural Resources), County (e.g., Anne Arundel, Prince Georges, Howard, Montgomery) governments and the natural resource management researchers (e.g., Smithsonian Environmental Research Center, University of Maryland Center for Environmental Studies), all of whom are partnered with the RESAC. Extensive demonstrations to present the results and the technology will be held including a 1-day workshop for all interested parties (commercial, research, non-profit, educational and governmental organizations at the local, state and federal levels).
Figure 6. Profile of canopy height, canopy density and subcanopy topography from an airborne laser altimeter over a forest (Salisbury MD.). The individual waveform contains multiple distinct returns. showing typical laser returns over a vegetation canopy. Canopy height is calculated by subtracting the elevations of the first and last returns.
Milestones
First quarter: September-October. Flight operations over the Patuxent watershed.
October-November. Data download to project computers.
Second Quarter: December-February Data processing to remove extraneous signals
Third Quarter: March-May Extraction of first and ground return data
Fourth Quarter June-August Generation of topography and canopy data
User workshop
References
Blair, J. B., D. L. Rabine and M. A. Hofton. 1999. The Laser Vegetation Imaging Sensor: a medium-altitude, digitization-only, airborne laser altimeter for mapping vegetation and topography. ISPRS Journal of Photogrammetry and Remote Sensing, 54: 115-122.
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