EAARL Coastal Topography--Northern Assateague Island National Seashore, Maryland and Virginia, 2003: Bare Earth

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Frequently anticipated questions:


What does this data set describe?

Title:
EAARL Coastal Topography--Northern Assateague Island National Seashore, Maryland and Virginia, 2003: Bare Earth
Abstract:
ASCII XYZ point cloud data were 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 northern 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.
Supplemental_Information:
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. 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 99). 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.
  1. How might this data set be cited?
    U.S. Geological Survey, 20170324, EAARL Coastal Topography--Northern Assateague Island National Seashore, Maryland and Virginia, 2003: Bare Earth: U.S. Geological Survey Data Release doi:10.5066/F7PV6HKJ, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.246544
    East_Bounding_Coordinate: -75.092368
    North_Bounding_Coordinate: 38.325799
    South_Bounding_Coordinate: 38.055490
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 25-Feb-2003
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set.
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 18N
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -75.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.01
      Ordinates (y-coordinates) are specified to the nearest 0.01
      Planar coordinates are specified in meters
      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 0.01 m
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:
      Explicit elevation coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    The attributes included in this data file are: NAD83 UTM Zone 18 easting values in meters, NAD83 UTM Zone 18 northing values in meters, NAVD88 elevations in meters and time as seconds of epoch (seconds).
    Entity_and_Attribute_Detail_Citation: http://pubs.usgs.gov/of/2009/1078/

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
    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.
  3. To whom should users address questions about the data?
    Christine Kranenburg
    Cherokee Nation Technologies, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Computer Scientist
    600 4th Street South
    St. Petersburg, FL
    USA

    727 502-8129 (voice)
    727 502-8182 (FAX)
    ckranenburg@usgs.gov
    Hours_of_Service: M-F, 8:00-4:00 ET

Why was the data set created?

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), 03LTS05. Additional survey and data details are available at http://cmgds.marine.usgs.gov/fan_info.php?fan=03LTS05.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 10-Jul-2003 (process 1 of 3)
    The data were collected using a Cessna 310 aircraft. The EAARL laser scanner collects the data using a green-wavelength (532-nanometer) raster scanning laser, while a digital camera acquires a visual record of the flight. The data are stored on hard drives and archived at the USGS office in St. Petersburg, Florida. Raw EAARL waveform, GPS, and Inertial Measurement Unit (IMU) data were subsequently loaded into ALPS software. ALPS (20030710), interactively processed small sections of the data to obtain best estimates of aircraft pitch and roll biases. Person who carried out this activity:
    Amar Nayegandhi
    ETI Professionals, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Computer Scientist
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8129 (voice)
    eaarl-meta@usgs.gov
    Hours_of_Service: M-F, 8:00-4:00 ET
    Date: 01-Apr-2004 (process 2 of 3)
    ALPS (20030710-20040401) was used to batch process the raw data for first and last return topography. Next, it batch filtered the point cloud using the interactive RCF. The input parameters of the RCF were: grid cell size (buffer) = 400 cm x 400 cm; vertical tolerance (vertical width) = 50 cm. The data were also datum converted from ITRF00 to NAD83, NAVD88 using the Geoid99 model. Person who carried out this activity:
    Amar Nayegandhi
    ETI Professionals, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Computer Scientist
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8129 (voice)
    eaarl-meta@usgs.gov
    Date: 23-Feb-2017 (process 3 of 3)
    The final .pbd (Portable Data Base) format files were loaded into ALPS (20170223) to remove any data from the tile buffers, merge the tiled data into a single product, clip the point cloud to the boundary of the NPS 2003 Assateague Island polygon and export the points to an ASCII XYZ file. Tile buffers are an overlap region extending 200 meters past the edges of the 2-Km tile and contain duplicate data from adjacent tiles. The final .xyz file consists of four columns: UTM Easting, UTM Northing, elevation, and time. Person who carried out this activity:
    Christine Kranenburg
    Cherokee Nation Technologies, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Computer Scientist
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8129 (voice)
    ckranenburg@usgs.gov
  3. What similar or related data should the user be aware of?
    Nayegandhi, A., Brock, J.C., and Wright, C.W., 2009, Small footprint, waveform-resolving lidar estimation of submerged and subcanopy topography in coastal environments: International Journal of Remote Sensing 30(4), p. 861-878.


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    The expected accuracy of the measured variables are as follows: attitude within 0.07 degree, 3-cm nominal ranging accuracy, and vertical elevation accuracy of +/-15 cm for the topographic surface. Quality checks are built into the data-processing software.
  2. How accurate are the geographic locations?
    Raw elevation measurements have been determined to be within 1 meter in horizontal accuracy.
  3. How accurate are the heights or depths?
    Point elevation measurements from the EAARL system have been determined to be within +/- 15 cm in vertical accuracy; however, a ground-control survey was not completed simultaneously with this lidar survey.
  4. Where are the gaps in the data? What is missing?
    These point-cloud data may appear sparse or nonexistent, which is a result of the survey not covering a particular region, automated filtering or automated clipping to the official NPS 2003 park boundary polygon for Assateague Island National Seashore.
  5. How consistent are the relationships among the observations, including topology?
    These data were processed for topography ONLY.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
Use_Constraints:
The U.S. Geological Survey requests to be acknowledged as originator of these data in future products or derivative research.
  1. Who distributes the data set? (Distributor 1 of 1)
    Christine Kranenburg
    Cherokee Nation Technologies, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Computer Scientist
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8129 (voice)
    ckranenburg@usgs.gov
  2. What's the catalog number I need to order this data set? ASIS2003_EAARLA_BE_z18_n88g99.xyz
  3. What legal disclaimers am I supposed to read?
    Although these data have been processed successfully on a computer system at the USGS, no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The USGS shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 24-Mar-2017
Metadata author:
Christine Kranenburg
Cherokee Nation Technologies, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
Computer Scientist
600 4th Street South
St. Petersburg, FL
USA

(727) 502-8129 (voice)
ckranenburg@usgs.gov
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/ASIS2003_EAARLA_BE_z18_n88g99_metadata.faq.html>
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