Assateague Island Sand Areas Extracted from Orthoimagery, 1989 - 2013

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Frequently anticipated questions:


What does this data set describe?

Title:
Assateague Island Sand Areas Extracted from Orthoimagery, 1989 - 2013
Abstract:
Assessing the physical change to shorelines and wetlands is critical in determining the resiliency of wetland systems that protect adjacent habitat and communities. The wetland and back-barrier shorelines of Assateague Island, located in Maryland and Virginia, changed as a result of wave action and storm surge that occurred during Hurricane Sandy, which made landfall on October 29, 2012. The impact of Hurricane Sandy will be assessed and placed in its historical context to understand the future vulnerability of wetland systems. Making these assessments will rely on data extracted from current and historical resources such as maps, aerial photographs, satellite imagery, and lidar elevation data, which document physical changes over time. This USGS Data Series publication includes several open-ocean shorelines, back-island shorelines, back-island shoreline points, sand area polygons, and sand lines for Assateague Island that were extracted from orthoimagery (ortho aerial photography) dated from April 12, 1989 to September 5, 2013. This dataset consists of polygons that represent the sand areas found in orthoimagery taken on the date specified in the filename and in the Date_ field in the feature attribute table. Orthoimagery of Assateague Island were acquired in digital format from U.S. Department of Agriculture (USDA), U.S. Geological Survey (USGS) and Virginia Geographic Information Network (VGIN) courtesy of the Commonwealth of Virginia. Prior to processing, the images were trimmed to the Assateague Island area. Using ERDAS Imagine 9.3, the images were classified into 10-40 classes that were coded either sand or not sand. Using ArcGIS 10.1, the resulting coded raster datasets were converted to polygons and edited. The following list provides additional details about the orthoimagery used. The sand areas for each date is in a separate dataset (shapefile) named asis_sand_po_*.shp where the date, in YYYYMMDD format, replaces the asterisk. The orthoimage date for each polygon is also included in the shapefile attribute table Date_ field.
Date State Type Source Resolution
198904129(1) MD DOQQ USGS 1 meter (m) 19940320 VA DOQQ USGS 1 m 20041105 VA NAIP USDA 2 m 20050608 VA NAIP USDA 2 m 20050615 MD NAIP USDA 1 m 20060528 VA NAIP USDA 2 m 20060701 MD NAIP USDA 2 m 20070622 MD NAIP USDA 1 m 20080525 VA NAIP USDA 1 m 20090626 MD NAIP USDA 1 m 20090726 VA NAIP USDA 1 m 20090807 VA NAIP USDA 1 m 20110530 VA NAIP USDA 1 m 20110602 MD NAIP USDA 1 m 20120512 VA NAIP USDA 1 m 20130315 VA VBMP VGIN(2) 1 m(3) 20130905 MD NAIP USDA 1 m
DOQQ Digital Orthophoto Quarter Quads NAIP National Agriculture Imagery Program VBMP Virginia Base Mapping Program
(1)Color Infrared orthoimagery; all others are natural color. (2)Imagery courtesy of the Commonwealth of Virginia. (3)Resampled from 1-foot resolution imagery.
  1. How might this data set be cited?
    U.S. Geological Survey, 2015, Assateague Island Sand Areas Extracted from Orthoimagery, 1989 - 2013: U.S. Geological Survey Data Series 928, U.S. Geological Survey, St. Petersburg, Fla..

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.413621
    East_Bounding_Coordinate: -75.089520
    North_Bounding_Coordinate: 38.325818
    South_Bounding_Coordinate: 37.850461
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 12-Apr-1989
    Ending_Date: 05-Sep-2013
    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 Vector data set. It contains the following vector data types (SDTS terminology):
      • GT-polygon composed of chains (2793)
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 18
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -75.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.6096
      Ordinates (y-coordinates) are specified to the nearest 0.6096
      Planar coordinates are specified in meter
      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 1980.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.
  7. How does the data set describe geographic features?
    asis_sand_po_*.shp
    Polygons representing sand areas on Assateague Island extracted from orthoimagery. (Source: USGS)
    FID
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: Esri) Coordinates defining the features.
    Date_
    Date of orthoimage source. (Source: USGS) Date in month, day, year formatted as text.

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 U.S. Geological Survey St. Petersburg Coastal and Marine Science Center Coastal and Marine Geology Program as a data source would be appreciated in products developed from these data, and such acknowledgment as is standard for citation and legal practices. 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.
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Kristy Guy
    600 4th St. S.
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    727-502-8181 (FAX)
    kguy@usgs.gov
    Hours_of_Service: Monday through Friday 9:00 AM to 5:00 PM (Eastern Time)

Why was the data set created?

These data were extracted from orthoimagery to document the changes to sand areas on Assateague Island due to Hurricane Sandy and over time since 1989. These data will aid in developing an assessment of the physical change in wetlands due to wave action and storm surge from Hurricane Sandy and in determining the resiliency of wetland systems that protect adjacent habitat and communities.

How was the data set created?

  1. From what previous works were the data drawn?
    USGS Orthoimagery (source 1 of 3)
    USGS, 2014, USGS DOQQ Orthoimagery: USGS, http://earthexplorer.usgs.gov/.

    Type_of_Source_Media: online
    Source_Contribution: This data source was used to identify sand areas.
    USDA Orthoimagery (source 2 of 3)
    U.S. Department of Agriculture (USDA), 2014, USDA NAIP Orthoimagery: USDA, http://datagateway.nrcs.usda.gov/GDGOrder.aspx.

    Type_of_Source_Media: online
    Source_Contribution: This data source was used to identify sand areas.
    VGIN Orthoimagery (source 3 of 3)
    Virginia Geographic Information Network (VGIN), 2013, VGIN Orthoimagery: VGIN, Richmond, VA.

    Type_of_Source_Media: digital hard drive
    Source_Contribution: This data source was used to identify sand areas.
  2. How were the data generated, processed, and modified?
    Date: 2014 (process 1 of 3)
    The orthoimagery was subset to the Assateague Island area. Using ERDAS Imagine 9.3, 10-40 classes were generated by using the unsupervised classification method set to principal axis initializing, 1 standard deviation, 10 iterations maximum, 0.95 convergence threshold, skip factor of 1 for both x and y (no skipping), and zeroes not classified. The resulting classes were examined and coded as either sand or not sand. Person who carried out this activity:
    USGS
    600 4th St. S.
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    727-502-8181 (FAX)
    Hours_of_Service: Monday through Friday 8:00 AM to 5:00 PM (Eastern Time)
    Contact_Instructions:
    If unable to reach the contact by telephone, please leave a voice message.
    Data sources used in this process:
    • USGS Orthoimagery
    • USDA Orthoimagery
    • VGIN Orthoimagery
    Data sources produced in this process:
    • Classified Imagery
    Date: 2014 (process 2 of 3)
    Using ArcGIS 10.1, the sand coded raster datasets were converted to polygons. Polygons outside the island were deleted. Polygons with areas less than 100 meters2 were deleted. The open-ocean shoreline edge of the polygons were trimmed and filled to a hand-digitized water line (the same-date open-ocean shoreline found within asis_sshrln_1989_2013.shp which is included in this Data Series publication) to simplify the irregular and misclassified areas caused by wet sand and waves. Person who carried out this activity:
    USGS
    600 4th St. S.
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    727-502-8181 (FAX)
    Hours_of_Service: Monday through Friday 8:00 AM to 5:00 PM (Eastern Time)
    Contact_Instructions:
    If unable to reach the contact by telephone, please leave a voice message.
    Data sources used in this process:
    • Classified Imagery
    Data sources produced in this process:
    • Sand Polygons
    Date: 13-Oct-2020 (process 3 of 3)
    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)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    The horizontal accuracy of the data are unknown.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    There are void areas due to processing the imagery in sections and incomplete image coverage.
  5. How consistent are the relationships among the observations, including topology?
    Assateague Island was divided into five sections and data were extracted by sections and later put together. This resulted in small gaps between sections. More than one unsupervised classification scheme may have been used on a single image due to quality variations within the image. None of the orthoimagery datasets covered the entire island. No adjustments were made for varying tide levels.

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:
None. However, variability in image quality from one date to another, from one image to another on the same date, and from one part of a single image to another part of the same image, exists due to many factors including variation in sun angle, atmospheric conditions, season, reflectivity of the earth surface, camera angle, camera lens, camera settings, film sensitivity, water turbidity, water depth, tide level, waves, and error in image rectification. No adjustments were made to account for tide level. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center Coastal and Marine Geology Program as the originator of these data in future products or derivative research.
  1. Who distributes the data set? (Distributor 1 of 1)
    Kristy Guy
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, Fla.
    GIS/RS Analyst
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    Hours_of_Service: Monday-Friday, 9:00-5:00 Eastern Time
  2. What's the catalog number I need to order this data set? DS 928
  3. What legal disclaimers am I supposed to read?
    Although these data were 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?
    • Availability in digital form:
      Data format: ArcGIS shapefile
      Network links: https://pubs.usgs.gov/ds/0928/downloads/sand_area_polygons.zip
    • Cost to order the data: None if obtained online; otherwise prices vary.

    • Special instructions:
      Publications are available from USGS Information Services, Box 25286, Federal Center, Denver, CO 80225-0046 (telephone: 1-888-ASK-USGS, e-mail: infoservices@usgs.gov).

Who wrote the metadata?

Dates:
Last modified: 13-Oct-2020
Metadata author:
USGS
Attn: Kristy Guy
600 4th Street South
St. Petersburg, FL
USA

727-502-8000 (voice)
727-502-8181 (FAX)
kguy@usgs.gov
Hours_of_Service: Monday through Friday 9:00 AM to 5:00 PM (Eastern Time)
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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