Originator: U.S. Geological Survey
EAARL-B Coastal Topography--Chandeleur Islands, Louisiana, 2012: Seamless (Bare Earth and Submerged) (.shp file)
Geospatial_Data_Presentation_Form: vector digital data
Series_Name: U.S. Geological Survey Data Series
Publication_Place: St. Petersburg, FL
Publisher: U.S. Geological Survey
This shapefile was produced from 52 2-kilometer by 2-kilometer tile extents of remotely sensed, geographically referenced elevation measurements by the U.S. Geological Survey (USGS). Elevation measurements were collected over the area using the second-generation Experimental Advanced Airborne Research Lidar (EAARL-B), 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 55 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 0.5 - 1.6 meters. The nominal vertical elevation accuracy expressed as the root mean square error (RMSE) is 15 centimeters. A peak sampling rate of 15 - 30 kilohertz 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 produce highly detailed and accurate digital elevation maps of a portion of the Chandeleur Islands, Louisiana, 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 originally by a USGS-NASA collaborative project. Specialized processing algorithms are used to convert raw waveform lidar data acquired by the EAARL-B to georeferenced spot (x,y,z) returns for "first surface" and "bare earth" topography. 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-B 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 GEOID12A model).
The development of custom software for creating these data products has been supported by the U.S. Geological Survey CMGP's Lidar for Science and Resource Management project. Processed data products are used by the U.S. Geological Survey CMGP'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_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: Airborne Lidar Processing System
Theme_Keyword: Digital Elevation Model
Theme_Keyword: Experimental Advanced Airborne Research Lidar
Theme_Keyword: laser altimetry
Theme_Keyword: Cessna 310
Theme_Keyword: remote sensing
Theme_Keyword_Thesaurus: Global Change Master Science Directory
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
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_Thesaurus: Geographic Names Information System
Place_Keyword: St. Bernard Parish
Place_Keyword: Chandeleur Islands
Place_Keyword: Gulf of Mexico
Stratum_Keyword: Seamless (bare earth and submerged)
The U.S. Geological Survey requests to be acknowledged as the originator of this file in future products or derivative research.
Contact_Person: Xan Fredericks
Contact_Position: Lidar Validation and Processing Analyst
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
Address_Type: mailing and physical address
Contact_Voice_Telephone: 727 502-8086
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 U.S. Geological Survey, 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 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.
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