Elevation of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia

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Frequently anticipated questions:

What does this data set describe?

Title:
Elevation of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia
Abstract:
Elevation distribution in the Assateague Island National Seashore (ASIS) salt marsh complex and Chincoteague Bay is given in terms of mean elevation of conceptual marsh units defined by Defne and Ganju (2018). The elevation data is based on the 1-meter resolution Coastal National Elevation Database (CoNED). Through scientific efforts initiated with the Hurricane Sandy Science Plan, the U.S. Geological Survey has been expanding national assessment of coastal change hazards and forecast products to coastal wetlands, including the Assateague Island National Seashore and Chincoteague Bay salt marshes, with the intent of providing Federal, State, and local managers with tools to estimate the vulnerability and ecosystem service potential of these wetlands. For this purpose, the response and resilience of coastal wetlands to physical factors need to be assessed in terms of the ensuing change to their vulnerability and ecosystem services.
References: Defne, Z., and Ganju, N.K., 2018, Conceptual marsh units for Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: U.S. Geological Survey data release, https://doi.org/10.5066/P92ZW4D9.
  1. How might this data set be cited?
    Defne, Zafer, and Ganju, Neil K., 2018, Elevation of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P9HCTQ66, U.S. Geological Survey, Reston, Virginia.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Defne, Z., and Ganju, N.K., 2018, Elevation of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: U.S. Geological Survey data release, https://doi.org/10.5066/P9HCTQ66.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.495501125
    East_Bounding_Coordinate: -75.096217831
    North_Bounding_Coordinate: 38.337742876
    South_Bounding_Coordinate: 37.845685405
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5ba3cb40e4b08583a5c81b7b?name=mu_elev_ASISp.png (PNG)
    Graphic that shows elevation in marsh units of ASIS and Chincoteague Bay salt marsh complex overlaying Esri basemap.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2018
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Vector Digital Data Set (Polygon)
  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):
      • G-polygon (3352)
    2. What coordinate system is used to represent geographic features?
      The map projection used is WGS 1984 Web Mercator Auxiliary Sphere (ESRI Full Name: WGS_1984_Web_Mercator_Auxiliary_Sphere).
      Projection parameters:
      Standard_Parallel: 0.0
      Longitude_of_Central_Meridian: 0.0
      False_Easting: 0.0
      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 D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    mu_elev_ASISp
    Attribute information associated with the mean elevation of the conceptual marsh units of ASIS and Chincoteague Bay salt marsh complex. (Source: Producer defined)
    FID
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: Esri) Coordinates defining the features.
    FID_CMU
    Sequential unique whole number that represents the identification number for each conceptual marsh units. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:3351
    Units:none
    ATOT_M2
    Total surface area of a marsh unit in square meters (Source: USGS)
    Range of values
    Minimum:199.285436
    Maximum:623041.914617
    Units:square meters
    AVEG_M2
    Surface area of vegetated part of a marsh unit in square meters (Source: USGS)
    Range of values
    Minimum:0
    Maximum:479882.968935
    Units:square meters
    mu_ELEV
    Mean elevation of a marsh unit in meters (Source: USGS)
    Range of values
    Minimum:-1.26906941184
    Maximum:2.11340797207
    Units:meters
    vg_ELEV
    Mean elevation of the vegetated area in a marsh unit in meters (Source: USGS)
    Range of values
    Minimum:-1.08603499852
    Maximum:2.01393309818
    Units:meters
    FLG
    Marsh unit flag indicating anomalous marsh units based on absence of vegetation, elevation and surface area. FLG values indicate: (-1) no vegetated area; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than 0.2 percentile; (-1000) marsh unit surface area less than 900 m2; and (0) no flag. Combination of negative values indicate combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m2. (Source: USGS)
    Range of values
    Minimum:-1101
    Maximum:0
    Units:None
    Entity_and_Attribute_Overview:
    In this dataset, mean elevation for each conceptual salt marsh unit in the ASIS and Chincoteague Bay salt marsh complex has been calculated based on the 1-meter resolution raster source dataset. Decimal values in the attribute table are a result of double precision calculations while significant digits are considered in defining the attribute measurement resolutions. Therefore, the smallest unit increment for area values and elevation is assumed to be 1 meter and 0.01, respectively.
    Entity_and_Attribute_Detail_Citation: USGS

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Zafer Defne
    • Neil K. Ganju
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Zafer Defne
    Ocean Scientist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2254 (voice)
    508-457-2310 (FAX)
    zdefne@usgs.gov

Why was the data set created?

The purpose of this shapefile is to calculate mean elevation for each marsh unit and its vegetated component. Analysis of marsh elevation is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes.

How was the data set created?

  1. From what previous works were the data drawn?
    CoNED (source 1 of 3)
    Danielson, Jeffrey, and Tyler, Dean, 2016, Topobathymetric Model for Chesapeake Bay Region - District of Columbia, States of Delaware, Maryland, Pennsylvania, and Virginia, 1859 to 2015: U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    Downloaded CoNED topobathymetric data from USGS Earth Explorer. Projection was NAD 1983 UTM Zone 18N with the North American Vertical Datum of 1988 (NAVD 88). Download date was 2017/10/26.
    NWI (source 2 of 3)
    U.S. Fish and Wildlife Service, 2017, HU8_02040303 Wetlands: U.S. Fish and Wildlife Service, Madison, WI.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    Downloaded wetlands data for the watershed containing the study domain in Shapefile format from the National Wetlands Inventory (NWI) download page. Projection was NAD 1983 Albers. Download date was 2017/10/27.
    CMU_ASISp.shp (source 3 of 3)
    Defne, Zafer, and Ganju, Neil K., 2018, Conceptual marsh units for Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P92ZW4D9, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    Used the features in [CMU_ASISp.shp] to calculate the mean elevation for each marsh unit. Projection was WGS 1984 Web Mercator Auxiliary Sphere.
  2. How were the data generated, processed, and modified?
    Date: 2018 (process 1 of 2)
    This process step and all subsequent process steps were performed by the same person, Zafer Defne, in ArcMap (ver. 10.5.1) using tools from ArcToolbox, unless otherwise stated. For complex operations, names of specific tools used are given in CAPITAL letters (any critical parameters used are given in parentheses, separated by a semicolon, immediately after the tool name). The input and output file names are provided in [square brackets] when necessary. Units for length and area calculations are meters (m) and square meters (m2) unless otherwise stated.
    a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 18N. Prepare elevation dataset to be clipped to the boundaries polygon. MOSAIC TO NEW RASTER(Pixel type= 32 bit float; Mosaic operator=Mean; Cellsize=1 m) all of the CoNED raster to a new raster dataset with 1 m resolution [elev_mosaic.tif].
    b) Calculate values for each marsh unit. DISSOLVE(Input features=[CMU_ASISp]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG with Statistics type= First) to dissolve the vegetated and unvegetated classes in each marsh unit. FLG flags anomalous marsh units based on absence of vegetation, elevation and surface area, and is set to (-1) no vegetated area; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than 0.2 percentile; (-1000) marsh unit surface area less than 900 m2; and (0) no flag. Combination of negative values indicate combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m2. PROJECT(Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=NAD 1983 UTM Zone 18N; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain dissolved marsh units [mu_diss.shp].
    c) Clip the raster with the polygon features by using EXTRACT BY MASK to obtain [elev_idw_mu.tif].
    d) ZONAL STATISTICS AS TABLE(Feature Zone Data=[mu_diss.shp]; zone field=FID_CMU; Value Raster=[elev_idw_mu.tif]; Output Table=mu; Statistics type=MEAN)
    e) ADD JOIN(Layer name=[mu_diss.shp]; Input join field=FID_CMU; Join Table=mu; Output join field=FID_CMU) to marsh units layer based on the "FID_CMU" field
    f) Export dataset as a shapefile [mu_elev.shp] and keep the 'mu_MEAN" and "mu_ATOT_M2" fields from the join operation.
    g) Calculate elevation of the vegetated areas only. SELECT BY ATTRIBUTES FROM [CMU_ASISp] where "CLASS"= 'vegetated'. SELECT BY ATTRIBUTES FROM [CMU_ASISp] where "CLASS"= 'vegetated'. Follow steps (c) to (f) using the selected features to export [veg_elev.shp].
    h) JOIN FIELD(Input table=[mu_elev.shp]; Input join field=mu_FID_CMU; Join table=[veg_elev.shp]; Output join field=vg_FID_CMU; Join fields=vg_AVEG_M2,vg_ATOT_M2,vg_MEAN). Change the field names to VG_ELEV and MU_ELEV respectively for the fields with the mean elevation for the vegetated area only and mean elevation for the entire marsh unit. Name AVEG_M2 and ATOT_M2 for vegetated and total area, respectively, and export to a new shapefile. [mu_elev_ASIS.shp].
    i) SELECT BY ATTRIBUTES FROM [CMU_ASISp] where "CLASS"= 'vegetated', and join field "APGN_M2" from CMU_ASISp.shp on the feature dataset [mu_elev_ASIS.shp].
    j) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Input coordinate system=NAD 1983 UTM Zone 18N; Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain the final conceptual marsh units [mu_elev_ASISp.shp]. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Zafer Defne
    Ocean Scientist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2254 (voice)
    508-457-2310 (FAX)
    zdefne@usgs.gov
    Data sources used in this process:
    • CMU_ASISp
    • CoNED
    Data sources produced in this process:
    • mu_elev_ASISp
    Date: 07-Aug-2020 (process 2 of 2)
    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?
    Defne, Zafer, and Ganju, Neil K., 2018, Conceptual marsh units for Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P92ZW4D9, U.S. Geological Survey, Reston, VA.

    Online Links:

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

  1. How well have the observations been checked?
    Marsh units, water and land boundary inherit their accuracy from accuracy of the source data, ASIS marsh units, and vertical accuracy of the 1-meter resolution U.S. Geological Survey Coastal National Elevation Database (USGS CoNED) data with processing date of 2016.
  2. How accurate are the geographic locations?
    Horizontal accuracy is inherited from the source dataset that delineates the marsh units, and can be considered to be +/-6 meters.
  3. How accurate are the heights or depths?
    Because the elevation values are averaged over delineated polygons, vertical accuracy depends on both the horizontal accuracy of NWI dataset and the vertical accuracy of source elevation data, CoNED. CoNED vertical elevation accuracy was 0.2 meters.
  4. Where are the gaps in the data? What is missing?
    The results are specific to the marsh polygons definition within the boundaries of the ASIS and Chincoteague Bay salt marsh complex. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries. Coverage near the domain boundaries in Wallops Bay and Wallops Island is not complete and not suggested for use in analyses (specifically marsh units with FID_CMU=3, 1659, 1666, 1672 and 1728).
  5. How consistent are the relationships among the observations, including topology?
    Positive elevation indicates above sea level. Marsh units with extremely low elevation (smaller than 0.2 percentile value), with extremely high elevation (larger than 99.8 percentile value) or with areas less than 900 square meters were flagged.

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 mean elevation for each marsh unit is defined for scientific research purposes and should not be used as a sole source of reference for any regulations and policy making. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the source of this information.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? mu_elev_ASISp
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 07-Aug-2020
Metadata author:
U.S. Geological Survey
Attn: Zafer Defne
Ocean Scientist
384 Woods Hole Road
Woods Hole, MA

508-548-8700 x2254 (voice)
508-457-2310 (FAX)
zdefne@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P9HCTQ66/mu_elev_ASISp.faq.html>
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