EAARL Submarine Topography-Florida Keys National Marine Sanctuary

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Frequently anticipated questions:

What does this data set describe?

EAARL Submarine Topography-Florida Keys National Marine Sanctuary
Lidar is a remote sensing technique that uses laser light to detect, range, or identify remote objects based on light reflected by the object or emitted through its subsequent fluorescence. Airborne ranging Lidar is now being applied in coastal environments to produce accurate, cost-efficient elevation datasets with high spatial density. The USGS in cooperation with NASA, NOAA, and NPS is using airborne Lidar to measure the submerged topography of the northern Florida reef tract; secondarily, the data will be assessed for its potential in terms of benthic characterization. Elevation measurements were collected over part of the Florida Keys National Marine Sanctuary (FKNMS) using the NASA Experimental Advanced Airborne Research Lidar (EAARL), a pulsed laser ranging system mounted onboard an aircraft to measure subaerial and submarine topography. The system uses a high frequency laser beam 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 EAARL system, developed by the NASA Wallops Flight Facility (WFF) in Virginia, measures ground elevation with a vertical resolution of roughly 15 centimeters. A sampling rate of up to 3 kHz results in an extremely dense spatial elevation data set. The EAARL system is typically flown at 300 m altitude AGL, resulting in a 240 m swath for each flightline. Data collection occurred with approximately 50% overlap between flightlines, resulting in about one laser sounding per square meter. The data were processed by the USGS FISC (St. Petersburg office) to produce 1 meter resolution raster images that can be easily ingested into a Geographic Information System (GIS). The data were organized as 2 km by 2 km data tiles in 32 bit floating-point integer GeoTIFF format.
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 and http://ngom.usgs.gov/dsp/tech/eaarl/index.php .
Raw Lidar data is not in a format that is generally usable by Park Service 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 converts raw Lidar data into a GIS-compatible map product to be provided to NPS 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 for the generation of subaerial and submarine Lidar topographic products. Specialized processing algorithms are used to convert raw waveform Lidar data acquired by the EAARL to geo-referenced spot (x,y,z) returns for submarine topography. These data are then converted to the North American (Horizontal ) Datum of 1983 (NAD83) and the North American Vertical Datum of 1988 (NAVD88, using the Geoid 03 model). The final products are 2x2-km map tiles written out in a standard GeoTIFF format with associated metadata information. These tiles are created for visual interpretation and regional quantitative analysis. Metadata files include the standard FGDC format.
  1. How might this data set be cited?
    U. S. Geological Survey, 2007, EAARL Submarine Topography-Florida Keys National Marine Sanctuary: Open File Report 2007-1395, U. S. Geological Survey, FISC St. Petersburg.

    Online Links:

    The USGS, in cooperation with the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA) and the National Park Service (NPS), provides the coastal management community with digital elevation products. The USGS processes aircraft liar data provided by NASA, develops software tools and algorithms to use and analyze the data, and makes products available to the coastal management community.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -80.455046
    East_Bounding_Coordinate: -80.235732
    North_Bounding_Coordinate: 25.197280
    South_Bounding_Coordinate: 24.963277
  3. What does it look like?
    http://pubs.usgs.gov/of/2007/1395/HTML/Images/sanctuary_image.gif (GIF)
    EAARL Submarine Topography - Florida Keys National Marine Sanctuary
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 17-Apr-2006
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: remote-sensing image
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 2001 x 2001 x 1, type Pixel
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 17
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -81.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1.000000
      Ordinates (y-coordinates) are specified to the nearest 1.000000
      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.
  7. How does the data set describe geographic features?
    This Digital Elevation Model is a GeoTiff derived from point data. It is raster data consisting of cells. Each cell has an elevation value associated with it. Cell size is 1 meter by 1 meter.
    This Digital Elevation Model is a GeoTIFF derived from point data referenced to WGS84, NAD83 UTM eastings and northings (m). The variables measured by EAARL are: distance between aircraft and GPS satellites (m), attitude information (roll, pitch, heading in degrees), scan angle (degrees), second of the epoch (sec), and 1-ns time-resolved return intensity waveform (digital counts). It is raster data consisting of cells. Each cell has an elevation value associ.,ated with it. Cell size is 1 meter by 1 meter.=G]

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?
    The U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg would like to acknowledge NASA Goddard Space Flight Center and NOAA National Geodetic Survey - Remote Sensing Division for their cooperation and assistance in the acquisition and processing of the data. The National Park Service also contributed by cleaning the Lidar dataset in preparation for map production.
  3. To whom should users address questions about the data?
    U.S. Geological Survey, FISC St. Petersburg
    Attn: Dr. John C. Brock
    Research Oceanographer
    600 4th Street South
    St. Petersburg, Florida

    (727) 803-8747 ext3088 (voice)
    (727) 803-2031 (FAX)
    Hours_of_Service: 8am to 5pm M-F EST

Why was the data set created?

The objective of this research is the creation of techniques for the surveying of submerged topography for the purposes of habitat mapping, ecological monitoring, change detection, and event assessment (e.g., hurricanes and extreme storm events). As part of this project, data from NASA EAARL were used. This sensor has the potential to make significant contributions in this realm for measuring shallow water depth and conducting cross-environment surveys. High spectral resolution and low costs were found to be key factors in providing accurate and affordable imagery to managers of coastal tropical habitats.

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: 2007 (process 1 of 4)
    The data are collected using a NOAA DeHavilland Twin Otter aircraft. The NASA Experimental Advanced Airborne Research Lidar (EAARL) laser scanner collects the data using a green (532nm) 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 and the NASA office at Wallops Flight Facility. The navigational data are processed at Wallops Flight Facility. The navigational and raw data are then downloaded into the Airborne Lidar Processing System (ALPS). Data are converted from units of time to x,y,z points for elevation. The derived surface data can then be converted into raster data (geotiffs). Person who carried out this activity:
    United States Geological Survey, FISC St. Petersburg
    Attn: Amar Nayegandhi
    Computer Scientist
    600 4th Street South
    St. Petersburg, Florida

    727-803-8747 (voice)
    Hours_of_Service: 8am to 5pm M-F EST
    Contact_Instructions: Call Survey for Details
    Date: 2007 (process 2 of 4)
    The raster dataset was opened in ERDAS IMAGINE for editing. An Area of Interest (AOI) polygon was drawn around regions of poor data quality. Poor data quality was determined visually by locating gaps in the data as well as artifacts of the Lidar processing. Pixels within the AOI polygons were given a raster value of -100 to correspond with other areas of No Data. Person who carried out this activity:
    National Park Service South Florida/Caribbean Network
    18001 Old Cutler Road, Suite 419
    Palmetto Bay, FL

    (305) 252-0347 (voice)
    (305) 253-0463 (FAX)
    Date: 08-Aug-2007 (process 3 of 4)
    Metadata imported into ArcCatalog from XML file. Person who carried out this activity:
    U.S. Geological Survey, FISC St. Petersburg
    600 4th Street South
    St. Petersburg, Florida

    727-803-8747 (voice)
    Date: 24-Jan-2017 (process 4 of 4)
    Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
  3. What similar or related data should the user be aware of?
    Brock, J.C.; Wright, C.W.; Sallenger, A.H; Krabill, W.B., and Swift, 2002, Basis and Methods of NASA Airborne Topographic Mapper Lidar Surveys for Coastal Studies: Journal of Coastal Research, West Palm Beach, Florida.

    Wright, C.W. and Brock, J.C., 2002, EAARL: A Lidar for mapping shallow coral reefs and other coastal environments: Proceedings of the Seventh International Conference on Remote Sensing for Marine and Coastal Environments, Miami, FL.

    John Brock and Asbury Sallenger, 2001, Airborne Topographic Lidar Mapping for Coastal Science and Resource Management: U.S. Geological Survey, St. Petersburg.

    Nayegandhi, A., Brock, J.C., Wright, C.W., OConnell, M.O., 2006, Evaluating a small-footprint, waveform-resolving Lidar over coastal vegetation communities: Photogrammetric Engineering and Remote Sensing, Maryland.

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 +/-20 cm for the submerged 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 horizontal accuracy. Processing steps (grid interpolation) may introduce additional error which has not been tested at the time of this publication.
  3. How accurate are the heights or depths?
    Elevations of the DEM are vertically consistent with the point elevation data, +/-20 cm.
  4. Where are the gaps in the data? What is missing?
    Several regions of the dataset are labeled as "No Data", which corresponds to a cell value of -100 m in the GeoTiff file. These "No Data" areas are a result of the survey not covering a particular region, optical water depth of greater than 1.5 Secchi disc depths, or the manual removal of Lidar processing artifacts.
  5. How consistent are the relationships among the observations, including topology?

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Any use of these data signifies a user's agreement to comprehension and compliance of the USGS Standard Disclaimer. Ensure all portions of metadata are read and clearly understood before using these data in order to protect both user and USGS interests. See section 6.3 Distribution Liability.
Although the USGS is making these data sets available to others who may find the data of value, USGS does not warrant, endorse, or recommend the use of these data for any given purpose. The user assumes the entire risk related to the use of these data. These data sets are not for navigational purposes. USGS is providing these data "as is", and USGS disclaims any and all warranties, whether expressed or implied, including (without limitation) any implied warranties of merchantability or fitness for a particular purpose. In no event will USGS be liable to you or to any third party for any direct, indirect, incidental, consequential, special, or exemplary damages or lost profits resulting from any use or misuse of these data.Acknowledgement of the U.S. Geological Survey, FISC - St. Petersburg as a data source would be appreciated in products developed from these data, and such acknowledgement as is standard for citation and legal practices for data source is expected by users of this data set. Sharing new data layers developed directly from these data would also be appreciated by USGS staff. Users should be aware that comparisons with other data sets for the same area from other time periods may be inaccurate due to inconsistencies resulting from changes in photo interpretation, mapping conventions, and digital processes over time. These data are not legal documents and are not to be used as such.
  1. Who distributes the data set? (Distributor 1 of 1)
    U. S. Gological Survery
    Attn: Jerry Butcher
    Windows System Administrator
    600 4th Street South
    St. Petersburg, Florida

    727-803-8747 ext3049 (voice)
    (727) 803-2031 (FAX)
    Hours_of_Service: 8am to 5pm M-F EST
  2. What's the catalog number I need to order this data set? EAARL Submarine Topography-Florida Keys National Marine Sanctuary
  3. What legal disclaimers am I supposed to read?
    The U. S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. These data and related graphics are not legal documents and are not intended to be used as such.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: TIFF (version 20070101) GeoTiff
      Network links: http://pubs.usgs.gov/of/2007/1395/HTML/data.html
      Media you can order: DVD (format DVD)
    • Cost to order the data: vary

    • Special instructions:
      Call U.S. Geological Survey for Details
  5. Is there some other way to get the data?
    Call U.S. Geological Survey for Details

Who wrote the metadata?

Last modified: 17-Apr-2018
Metadata author:
U.S. Geological Survey, FISC St. Petersburg
600 4th Street South
St. Petersburg, Florida

727-803-8747 (voice)
Hours_of_Service: 8am to 5pm M-F EST
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/of2007-1395metadata.faq.html>
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