Elevation of marsh units in eastern Long Island salt marsh complex, New York

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Frequently anticipated questions:


What does this data set describe?

Title:
Elevation of marsh units in eastern Long Island salt marsh complex, New York
Abstract:
This data release contains coastal wetland synthesis products for the geographic region of eastern Long Island, New York, including the north and south forks, Gardiners Island, and Fishers Island. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model, providing the spatial variability of physical factors that influence wetland health. 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 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.
  1. How might this data set be cited?
    Welk, Robert, Defne, Zafer, and Ganju, Neil, 20200331, Elevation of marsh units in eastern Long Island salt marsh complex, New York: data release DOI:10.5066/P91H426U, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Welk, Robert, Defne, Zafer, and Ganju, Neil, 2020, Coastal wetlands of eastern Long Island, New York: data release DOI:10.5066/P91H426U, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Welk, R., Defne, Z., and Ganju, N.K., 2020, Coastal wetlands of eastern Long Island, New York: U.S. Geological Survey data release, https://doi.org/10.5066/P91H426U
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -72.748198
    East_Bounding_Coordinate: 71.885316
    North_Bounding_Coordinate: 41.291362
    South_Bounding_Coordinate: 40.766433
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5ddd7472e4b04a30051ac165?name=elev_ELI_browse.png (PNG)
    Graphic that shows elevation of conceptual marsh units of the eastern Long Island salt marsh complex.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2020
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Vector Digital dataset (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 (2828)
    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.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 0.001
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method: Attribute values
  7. How does the data set describe geographic features?
    mu_elev_ELI
    Attribute information associated with the mean elevation of the conceptual marsh units of the eastern Long Island salt marsh complex. (Source: U.S. Geological Survey)
    FID
    Internal feature number. (Source: Esri) Unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: Esri) Coordinates defining the features.
    FID_CMU
    Unique whole numbers used to identify each conceptual marsh unit. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:3455
    Units:none
    ATOT_M2
    Total surface area of a marsh unit in square meters (Source: USGS)
    Range of values
    Minimum:8.876088
    Maximum:1278469.79671
    Units:square meters
    AVEG_M2
    Surface area of vegetated part of a marsh unit in square meters. Value is set to -9999 if there is no vegetated area in the marsh unit. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:1189344.84656
    Units:square meters
    VG_ELEV
    Mean elevation of the vegetated area in a marsh unit in meters. VG_ELEV and MU_ELEV is set to -999 if a no data cell value is provided in the input DEM to indicate the absence of real elevation values. Value is set to -9999 if there is no vegetated area in the marsh unit. (Source: USGS)
    Range of values
    Minimum:-1.46468
    Maximum:6.781148
    Units:meters
    MU_ELEV
    Mean elevation of a marsh unit in meters. MU_ELEV is set to -999 if a no data cell value is provided in the input DEM to indicate the absence of real elevation values. (Source: USGS)
    Range of values
    Minimum:-1.499292
    Maximum:6.779818
    Units:meters
    LOW3RD
    LOW3RD is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. Values of -9999 indicate no vegetated area within the marsh unit. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:98.919
    SKWNSS
    SKWNSS is the measure of skewness of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values i.e. right-skewed distribution indicate clustering of elevation distribution towards lower elevations. Negative numbers indicate a left-skewed distribution and clustering towards higher elevations. Values of -9999 indicate no vegetated area within the marsh unit. (Source: USGS)
    Range of values
    Minimum:-7.28295
    Maximum:8.64891
    MU_HFAR
    Ratio of DEM hydroflattend area in marsh unit. If MU_HFAR > 0.25, MU_ELEV is set to -9999. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:1
    VG_HFAR
    Ratio of DEM hydroflattend area in marsh unit. If VG_HFAR > 0.25, VG_ELEV is set to -9999. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:1
    FLG
    Marsh unit flag indicating anomalous marsh units based on elevation, surface area, and absence of vegetation. 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; (-200) greater than 25% of marsh unit has hydroflattened area (and has -9999 as its elevation value; (-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:-11200
    Maximum:0
    Units:None
    Entity_and_Attribute_Overview:
    In this dataset, mean elevation for each conceptual salt marsh unit in the eastern Long Island 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)
    • Robert Welk
    • Zafer Defne
    • Neil Ganju
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Robert Welk
    Hydrologic Technician
    2045 NY 112
    Coram, NY

    631-736-0783 x141 (voice)
    rwelk@usgs.gov

Why was the data set created?

The purpose of this shapefile is to calculate the 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. Elevation distribution in the eastern Long Island salt marsh complex is given in terms of mean elevation of conceptual marsh units. The elevation data is based on the 1-meter resolution National Elevation Database (NED).

How was the data set created?

  1. From what previous works were the data drawn?
    NED (source 1 of 4)
    U.S. Geological Survey, 2015, National Elevation Dataset: U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution:
    Downloaded NED Digital Elevation Model from the National Map. Projection was NAD 1983 UTM Zone 18N with the North American Vertical Datum of 1988 (NAVD 88). Download date was 2019/08/01.
    NAIP (source 2 of 4)
    U.S. Geological Survey, 2017, NAIP Digital Ortho Photo Image: USDA-FSA-APFO Aerial Photography Field Office, Salt Lake City, Utah.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution:
    Downloaded NAIP 1-meter resolution imagery from the USGS Earth Explorer. Projection was WGS 1984 Web Mercator Auxiliary Sphere. Download date was 2019/08/01.
    NWI (source 3 of 4)
    U.S. Fish and Wildlife Service, 2017, National Wetland Inventory New York Wetlands: U.S. Fish and Wildlife Service, Madison, WI.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution:
    Downloaded wetlands data for the state of New York in Shapefile format from the NWI download page. Projection was NAD 1983 Albers. Download date was 2018/08/01.
    NYSDEC (source 4 of 4)
    New England Interstate Water Pollution Control Commission, Prepared by Cameron Engineering and Associates, LLP, 2015, Long Island Tidal Wetlands Trends Analysis.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution:
    Wetland polygon shapefile prepared for Long Island Tidal Wetlands Trends Analysis. Data available by request. Data acquired 2019/05/01.
  2. How were the data generated, processed, and modified?
    Date: 2019 (process 1 of 2)
    This process step and all subsequent process steps were performed by the same person, Robert Welk, in ArcMap (ver. 10.6.1) 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) the entire NED raster to a new raster dataset with 1 m resolution [elev_mosaic.tif].
    b) Calculate values for each marsh unit. DISSOLVE(Input features=[CMU_ELI]; 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 a 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_ELI] 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. Set VG_ELEV to -9999 if there is no vegetated area in the marsh unit. Name AVEG_M2 and ATOT_M2 for vegetated and total area, respectively, and export to a new shapefile. [mu_elev_ELI.shp].
    i) Calculate metrics that quantify the distribution of marsh unit elevation values. SKWNSS is the measure of skewness of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values, i.e. right-skewed distributions, indicate clustering of elevation distributions towards lower elevations. Negative numbers indicate a left-skewed distribution and clustering towards higher elevations. LOW3RD is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. SKWNSS and LOW3RD parameters are calculated by applying the formulation of Raposa et al. (2016) to the elevation raster within the vegetated part of each marsh unit.
    j) SELECT BY ATTRIBUTES FROM [CMU_ELI] where "CLASS"= 'vegetated', and join field "APGN_M2" from CMU_ELI.shp on the feature dataset [mu_elev_ELI.shp].
    k) Calculate ratio of hydroflattend area in each marsh unit. Reclassify NED elevation raster with RASTER CALCULATOR (expression: SetNull('elev_mosaic.tif' == -1, 'elev_mosaic.tif') to get [elev_null.tif]. ZONAL STATISTICS AS TABLE (Input table=[mu_elev.shp, Zone field=FID_CMU], Input value raster=elev_null.tif, Statistics type=Mean) to get [hfar_mu]. ADD FIELD to output table 'MU_HFAR' and use FIELD CALCULATOR ((1-MEAN/2)). JOIN FIELD(Input Table=mu_elev.shp, Input Join Field=FID_CMU, Join Table=hfar_mu, Output Join Field=FID_CMU). If 'MU_HFAR' > 0.25, set 'mu_elev' = 0.
    l) Calculate ratio of hydroflattend area in the vegetated area of each marsh unit. ZONAL STATISTICS AS TABLE (Input table=[veg_elev.shp, Zone field=FID_CMU], Input value raster=elev_null.tif, Statistics type=Mean) to get [hfar_veg]. ADD FIELD to output table 'VG_HFAR' and use FIELD CALCULATOR ((1-MEAN/2)). JOIN FIELD(Input Table=mu_elev.shp, Input Join Field=FID_CMU, Join Table=hfar_veg, Output Join Field=FID_CMU). If 'MG_HFAR' > 0.25, set 'vg_elev' = 0.
    m) 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_ELI.shp].
    Reference: Raposa, K. B., Wasson, K., Smith, E., Crooks, J. A., Delgado, P., Fernald, S. H., et al. (2016). Assessing tidal marsh resilience to sea-level rise at broad geographic scales with multi-metric indices. Biological Conservation, 204, 263–275. https://doi.org/10.1016/J.BIOCON.2016.10.015 Data sources used in this process:
    • elev_mosaic
    • CMU_ELI
    • NAIP
    Date: 06-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?

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

  1. How well have the observations been checked?
    Marsh units and water and land boundaries inherit their horizontal accuracy from the accuracy of the source data, the eastern Long Island marsh units, and their vertical accuracy from the 2015 U.S. Geological Survey National Elevation Database (USGS NED).
  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 the NWI dataset and the vertical accuracy of the source elevation data, NED. NED vertical elevation accuracy is 0.2 meters.
  4. Where are the gaps in the data? What is missing?
    The results are specific to the marsh polygons as defined within the boundaries of the eastern Long Island 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.
  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), extremely high elevation (larger than 99.8 percentile value) or 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_ELI.shp (and other files associated with a shapefile), browse graphic (elev.png), and CSDGM metadata in XML format.
  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: 06-Aug-2020
Metadata author:
U.S. Geological Survey, Northeast Region
Attn: Robert J Welk
Hydrologic Technician
2045 Route 112
Coram, NY
US

631-736-0783 x141 (voice)
rwelk@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_P91H426U/mu_elev_ELI.faq.html>
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