Originator: U.S. Geological Survey
EAARL Coastal Topography--Assateague Island National Seashore, Maryland and Virginia, 2005: Bare Earth
Geospatial_Data_Presentation_Form: raster digital data
Series_Name: U.S. Geological Survey Data Release
Publication_Place: St. Petersburg, FL
Publisher: U.S. Geological Survey
A bare-earth topography Digital Elevation Model (DEM) mosaic for the Assateague Island National Seashore was produced from remotely sensed, geographically referenced elevation measurements acquired cooperatively by the U.S. Geological Survey (USGS) and the National Park Service (NPS). Elevation measurements were collected over Assateague Island National Seashore using the first-generation National Aeronautics and Space Administration (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 60 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 NASA at Wallops Flight Facility in Virginia, measures ground elevation with a vertical resolution of 3 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 purpose of this project was to provide highly detailed and accurate elevation data of the Assateague Island National Seashore in Maryland and Virginia, for use as a management tool and to make these data available to natural-resource managers and research scientists. To ensure that St. Petersburg Coastal and Marine Science Center (SPCMSC) data management protocols were followed, this survey was assigned a USGS field activity number (FAN), 05LTS12. Additional survey and data details are available at http://cmgds.marine.usgs.gov/fan_info.php?fan=05LTS12
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 USGS'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 originally 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 "first returns" are indicative of vegetation-canopy height, or bare ground in the absence of vegetation, whereas "last returns" typically represent "bare-earth" elevations under vegetation. The terms first surface and bare earth refer to the digital elevation data of the terrain, but while first-surface data include vegetation, buildings, and other manmade structures, bare-earth data do not. The zero crossing of the second derivative (that is, detection of stationary points) is used to detect the first return, resulting in "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" (the first and last returns being the first and last significant measurable portion of the return pulse). 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 (Geoid 12B).
The development of custom software for creating these data products has been supported by the USGS CMGP's Lidar for Science and Resource Management project. Processed data products are used by the USGS CMGP's National Assessment 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_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: Airborne Lidar Processing System
Theme_Keyword: Experimental Advanced Airborne Research Lidar
Theme_Keyword: laser altimetry
Theme_Keyword: remote sensing
Theme_Keyword: USGS National Assessment Project
Theme_Keyword: Digital Elevation Model
Theme_Keyword_Thesaurus: Global Change Master Science Directory
Theme_Keyword: LAND SURFACE > TOPOGRAPHY > TERRAIN ELEVATION
Theme_Keyword: OCEAN > COASTAL PROCESSES > BARRIER ISLANDS
Theme_Keyword: OCEAN > COASTAL PROCESSES > BEACHES
Theme_Keyword: OCEAN > COASTAL PROCESSES > SHORELINE DISPLACEMENT
DOI/USGS/CMG > COASTAL AND MARINE GEOLOGY, U.S. GEOLOGICAL SURVEY, U.S. DEPARTMENT OF INTERIOR
Theme_Keyword_Thesaurus: GCMD Instrument
Theme_Keyword: LIDAR > LIGHT DETECTION AND RANGING
Place_Keyword_Thesaurus: Geographic Names Information System
Place_Keyword: Assateague Island
Place_Keyword: Atlantic Ocean
Stratum_Keyword: Bare earth
The U.S. Geological Survey requests to be acknowledged as originator of these data in future products or derivative research.
Contact_Person: Christine Kranenburg
Contact_Position: Computer Scientist
Cherokee Nation Technologies, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
Address_Type: mailing and physical address
Contact_Voice_Telephone: 727 502-8129
Contact_Facsimile_Telephone: 727 502-8182
Hours_of_Service: M-F, 8:00-4:00 ET
Address: 600 4th Street South
City: St. Petersburg
Acknowledgment of the USGS St. Petersburg Coastal and Marine 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 of new data layers developed directly from these data would also be appreciated by the USGS 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 7 Version 6.1 (Build 7601) Service Pack 1; Esri ArcGIS 10.3.1.4959
Originator: Nayegandhi, A., 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