EAARL Topography-Dry Tortugas National Park

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Frequently anticipated questions:

What does this data set describe?

Title: EAARL Topography-Dry Tortugas National Park
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 it subsequent fluorescence. Airborne ranging lidar is now being applied in coastal environments to produce accurate, cost-efficient elevation datasets with high data density. The USGS in cooperation with NASA and NPS is using airborne lidar to measure the submerged topography of the Dry Tortugas reef tract and Subaerail topography of land features; secondarily, the data will be assessed for its potential in terms of benthic characterization. Elevation measurements were collected over Dry Tortugas National Park using the NASA Experimental Advanced Airborne Research Lidar (EAARL), a pulsed laser ranging system mounted onboard an aircraft to measure subaerial and submarine coastal topography. With the NASA EAARL lidar system, submarine data is generally acquired to a maximum of approximately 1.5 secchi depths (a measure of water clarity). 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 Experimental Advanced Airborne Research Lidar, developed by the National Aeronautics and Space Administration (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.
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 National Park Service 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 use of subaerial and submarine lidar in coastal change assessment. Specialized processing algorithms are used to convert raw waveform lidar data acquired by the EAARL to georeferenced spot (x,y,z) returns for submarine topography. These data are then converted to the NAD83 horizontal and NAVD88 vertical datum (using the Geoid 99 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, 2006, EAARL Topography-Dry Tortugas National Park: EAARL Lidar Submarine Topographic Maps 1244.

    Online Links:

    The USGS, in cooperation with the National Park Service (NPS) and the National Aeronautics and Space Administration (NASA), provide the coastal management community with digital elevation products. The USGS processes aircraft lidar 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: -82.995382
    East_Bounding_Coordinate: -82.758906
    North_Bounding_Coordinate: 24.746056
    South_Bounding_Coordinate: 24.545514
  3. What does it look like?
    e298n2722.tif (TIFF)
    gridplot tiff image
    http://pubs.usgs.gov/of/2006/1244/HTML/images/drto_map3.gif (GIF)
    Dry Tortugas National Park
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 31-Jul-2004
    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 2000 x 2000 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.
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: .01
      Altitude_Distance_Units: meters
      Explicit elevation coordinate included with horizontal coordinates
      Depth_Datum_Name: North American Vertical Datum of 1988
      Depth_Resolution: .01
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    This Digital Elevation Model is an 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 an 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 associated with it. Cell size is 1 meter by 1 meter.

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 USGS Center for Coastal and Watershed Studies would like to acknowledge NASA Goddard Space Flight Center for their cooperation and assistance in the development of the data. The USGS would also like to acknowledge Park Management and personnel at Dry Tortugas National Park. The National Park Service also contributed by editing the lidar tiles to remove processing artifacts.
  3. To whom should users address questions about the data?
    United States Geological Survey, Center for Coastal and Watershed Studies
    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: Monday-Friday, 8-5, EST

Why was the data set created?

One objective of this research is the creation of techniques for the surveying of coral reefs for the purposes of habitat mapping, ecological monitoring, change detection, and event assessment (e.g., bleaching, hurricanes, disease outbreaks, etc.). As part of this project, data from an innovative instrument developed at NASA Wallops Flight Facility, the NASA Experimental Airborne Advanced Research Lidar (EAARL), was used. This sensor has the potential to make significant contributions in this realm for measuring water depth and conducting cross-environment surveys. High spectral resolution, water-column correction, 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?
    none (source 1 of 1)
    NASA Collected the EAARL Lidar data and distributed to USGS for processing, 2006, EAARL Topography-Dry Tortugas National Park.

    Type_of_Source_Media: Point elevation measurements collected by the EAARL sensor.
    Source_Contribution: none
  2. How were the data generated, processed, and modified?
    Date: 2004 (process 1 of 4)
    The data are collected using a Cessna 310 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 Center for Coastal and Watershed Studies
    Attn: Amar Nayegandhi
    Computer Scientist
    600 4th Street South
    St. Petersburg, Florida

    727-803-8747 (voice)
    Hours_of_Service: 8:00am to 5:00pm Monday thru Friday, EST
    Contact_Instructions: Call Survey for Details
    Date: 01-Mar-2006 (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 Inventory and Monitoring Program
    Attn: Judd Patterson
    Research Assistant
    18001 Old Cutler Road
    Miami, Florida

    (305) 252-0347 (voice)
    (305) 253-0463 (FAX)
    Date: 24-Jan-2017 (process 3 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)
    Date: 13-Oct-2020 (process 4 of 4)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (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, R.N, 2003, Basis and Methods of NASA Ariborne Topographic Mapper Lidar Surveys for Coastal Studies: Journal of Coastal Research, West Palm Beach, FL.

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

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

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 "first return" 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?
    Each file contains data located in a 2-km by 2-km tile, where the upper-left bound can be assessed quickly through the file name. The first 3 numbers in the file name 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 (for example, ba_e123_n4567_20).

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 thes 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 Center for Coastal and Watershed Studies as a data source would be appreciated in products developed from these data, and such acknowledgement as is standad for citation and legal practices for data source is expected by users of this data. 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)
    United States Geological Survey
    Attn: Jerry Butcher
    Windows System Administrator
    600 4th Street South
    St. Petersburg, FL

    727-803-8747 ext3049 (voice)
  2. What's the catalog number I need to order this data set? Lidar DEM (date - identifier)
  3. What legal disclaimers am I supposed to read?
    The United States 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.The information contained in these data is dynamic and may change over time. The data are not better than the original sources from which they were derived. It is the responsibility of the data user to use the data appropriately and consistent within the limitations of geospatial data in general and these data in particular. The related graphics are intended to aid the data user in acquiring relevant data; it is not appropriate to use the related graphics as data.The United States Geological Survey gives no warranty, expressed or implied, as to the accuracy, reliability, or completeness of these data. It is strongly recommended that these data are directly acquired from an USGS server and not indirectly through other sources which may have changed the data in some way. Although these data have been processed successfully on a computer system at the United States Geological Survey, no warranty expressed or implied is made regarding the utility of the data on another system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: GeoTIFF GeoTIFF
      Network links: http://pubs.usgs.gov/of/2006/1244/HTML/raw_data.htm
      Media you can order: DVD (format DVD)
    • Cost to order the data: Vary

    • Special instructions:
      Contact U.S. Geological Survey.
    • How long will it take to get the data?
  5. Is there some other way to get the data?
    Call USGS for Details

Who wrote the metadata?

Last modified: 09-Nov-2021
Metadata author:
United States Geological Survey, St. Petersburg Coastal and Marine Science Center
Attn: SPCMSC Data Management Group
600 4th Street South
St. Petersburg, Florida

727-502-8000 (voice)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/of2006-1244metadata.faq.html>
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