Originator: U.S. Geological Survey
EAARL Coastal Topography--Assateague Island National Seashore, 2008: Bare Earth
Geospatial_Data_Presentation_Form: remote-sensing image
Series_Name: U.S. Geological Survey Data Series
Publication_Place: St. Petersburg, FL
Publisher: U.S. Geological Survey
A bare-earth elevation map (also known as a Digital Elevation Model, or DEM) of the Assateague Island National Seashore in Virginia and Maryland was produced from remotely sensed, geographically referenced elevation measurements cooperatively by the U.S. Geological Survey (USGS), the National Park Service (NPS), and the National Aeronautics and Space Administration (NASA). Elevation measurements were collected over the area using the NASA 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. The EAARL, developed by 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 subsequent elevation maps for an area are analyzed, they provide a useful tool to land managers.
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
The purpose of this project was to produce a highly detailed and accurate bare-earth digital elevation map of the Assateague Island National Seashore in Virginia and Maryland for use as a management tool and to make these data available to natural-resource managers and research scientists.
Raw lidar data are not in a format that is generally usable by resource managers and scientists for scientific analysis. Converting dense lidar elevation data into a readily usable format without loss of essential information requires specialized processing. The U.S. Geological Survey's Coastal and Marine Geology Program (CMGP) has developed custom software to convert raw lidar data into a GIS-compatible map product to be provided to GIS specialists, managers, and scientists. The primary tool used in the conversion process is Airborne Lidar Processing System (ALPS), a multi-tiered processing system developed by a USGS-NASA collaborative project. Specialized processing algorithms are used to convert raw waveform lidar data acquired by the EAARL to georeferenced spot (x,y,z) returns for "first surface" and "bare earth" topography. The zero crossing of the second derivative (that is, detection of local maxima) is used to detect "first surface" topography, while the trailing edge algorithm (that is, the algorithm searches for the location prior to the last return where direction changes along the trailing edge) is used to detect the range to the last return or "bare earth". Statistical filtering, known as the Random Consensus Filter (RCF), is used to remove false bottom returns and other outliers from the EAARL topography data. The filter uses a grid of non-overlapping square cells (buffer) of user-defined size overlaid onto the original point cloud. The user also defines the vertical tolerance (vertical width) based on the topographic complexity and point sampling density of the data. The maximum allowable elevation range within a cell is established by this vertical tolerance. An iterative process searches for the maximum concentration of points within the vertical tolerance, and removes those points outside of the tolerance (Nayegandhi and others, 2009). These data are then converted to the North American Datum of 1983 and the North American Vertical Datum of 1988 (using the GEOID03 model). Each file contains data located in a 2-kilometer by 2-kilometer tile, where the upper-left bound can be assessed quickly through the filename. The first 3 numbers in the filename represent the left-most UTM easting coordinate (e###000) in meters, the next 4 numbers represent the top-most UTM northing coordinate (n####000) in meters, and the last 2 numbers (##) represent the UTM zone in which the tile is located (ex. be_e123_n4567_18).The development of custom software for creating these data products has been supported by the U.S. Geoloigcal Survey CMG Program's Decision Support for Coastal Parks, Sanctuaries, and Preserves Project. Processed data products are used by the U.S. Geoloigcal Survey CMG Program's National Assessments of Coastal Change Hazards Project to quantify the vulnerability of shorelines to coastal change hazards such as severe storms, sea-level rise, and shoreline erosion and retreat.
Currentness_Reference: ground condition
Maintenance_and_Update_Frequency: None planned
Theme_Keyword_Thesaurus: USGS Metadata Identifier
Theme_Keyword: Airborne Lidar Processing System
Theme_Keyword: Digital Elevation Model
Theme_Keyword: Experimental Advanced Airborne Research Lidar
Theme_Keyword: laser altimetry
Theme_Keyword: remote sensing
Theme_Keyword_Thesaurus: Data Categories for Marine Planning
Theme_Keyword: bathymetry and elevation
Theme_Keyword_Thesaurus: Marine Realms Information Bank (MRIB) Keywords
Theme_Keyword: topographic mapping
Theme_Keyword_Thesaurus: USGS Thesaurus
Theme_Keyword: digital elevation models
Place_Keyword: Assateague Island National Seashore
The U.S. Geological Survey, National Park Service, and National Aeronautics and Space Administration request to be acknowledged as originators of this data in future products or derivative research.
Contact_Person: Amar Nayegandhi
Contact_Position: Computer Scientist
Jacobs Technology, U.S. Geological Survey, FISC, St. Petersburg, FL
Address_Type: mailing and physical address
Contact_Voice_Telephone: 727 803-8747 (x3026)
Hours_of_Service: M-F, 8:00-5:00 EST
Address: 600 4th Street South
City: St. Petersburg
Acknowledgment of the U.S. Geological Survey, Florida Integrated Science Center, as a data source would be appreciated in products developed from these data, and such acknowledgment as is standard for citation and legal practices for data source is expected. Sharing new data layers developed directly from these data would also be appreciated by the U.S. Geological Survey staff. Users should be aware that comparisons with other datasets for the same area from other time periods may be inaccurate due to inconsistencies resulting from changes in photointerpretation, mapping conventions, and digital processes over time. These data are not legal documents and are not to be used as such.
Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 220.127.116.110
Originator: Nayegandhi, Amar, Brock, J.C., and Wright, C.W.
Small footprint, waveform-resolving lidar estimation of submerged and subcanopy topography in coastal environments
Series_Name: International Journal of Remote Sensing
Issue_Identification: 30(4), p. 861-878