NAH_CCB_sedcover: Sediment Texture Units of the Sea Floor from Nahant to Northern Cape Cod Bay, Massachusetts (polygon shapefile, Geographic, WGS84)

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Frequently anticipated questions:

What does this data set describe?

Title:
NAH_CCB_sedcover: Sediment Texture Units of the Sea Floor from Nahant to Northern Cape Cod Bay, Massachusetts (polygon shapefile, Geographic, WGS84)
Abstract:
These data are qualitatively derived interpretive polygon shapefiles and selected source raster data defining surficial geology, sediment type and distribution, and physiographic zones of the sea floor from Nahant to Northern Cape Cod Bay. Much of the geophysical data used to create the interpretive layers were collected under a cooperative agreement among the Massachusetts Office of Coastal Zone Management (CZM), the U.S. Geological Survey (USGS), Coastal and Marine Geology Program, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Army Corps of Engineers (USACE). Initiated in 2003, the primary objective of this program is to develop regional geologic framework information for the management of coastal and marine resources. Accurate data and maps of seafloor geology are important first steps toward protecting fish habitat, delineating marine resources, and assessing environmental changes because of natural or human effects. The project is focused on the inshore waters of coastal Massachusetts. Data collected during the mapping cooperative involving the USGS have been released in a series of USGS Open-File Reports (<http://woodshole.er.usgs.gov/project-pages/coastal_mass/html/current_map.html>). The interpretations released in this study are for an area extending from the southern tip of Nahant to Northern Cape Cod Bay, Massachusetts. A combination of geophysical and sample data including high resolution bathymetry and lidar, acoustic-backscatter intensity, seismic-reflection profiles, bottom photographs, and sediment samples are used to create the data interpretations. Most of the nearshore geophysical and sample data (including the bottom photographs) were collected during several cruises between 2000 and 2008. More information about the cruises and the data collected can be found at the Geologic Mapping of the Seafloor Offshore of Massachusetts Web page: <http://woodshole.er.usgs.gov/project-pages/coastal_mass/>.
  1. How should this data set be cited?

    Pendleton, Elizabeth, 2013, NAH_CCB_sedcover: Sediment Texture Units of the Sea Floor from Nahant to Northern Cape Cod Bay, Massachusetts (polygon shapefile, Geographic, WGS84): Open-File Report 2012-1157, 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.

    Pendleton, E.A., Baldwin, W.E., Barnhardt., W.A., Ackerman, S.D., Foster, D.S., Andrews, B.D., and Schwab, W.C., 2013, Shallow Geology, Seafloor Texture, and Physiographic Zones of the Inner Continental Shelf from Nahant to Northern Cape Cod Bay, Massachusetts: Open-File Report 2012-1157, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -71.051972
    East_Bounding_Coordinate: -70.154205
    North_Bounding_Coordinate: 42.459855
    South_Bounding_Coordinate: 41.932269

  3. What does it look like?

    <http://pubs.usgs.gov/of/2012/1157/GIS_catalog/SedimentTexture/sedcover_browse.png> (PNG)
    Image of the sediment texture and distribution shapefile for the Massachusetts inner continental shelf from Nahant to Northern Cape Cod Bay

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 01-Jan-1994
    Ending_Date: 07-May-2008
    Currentness_Reference:
    ground condition of the source data that this interpretation is based on

  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):

      • G-polygon (491)

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.

      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 1
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method: Attribute values
      Depth_System_Definition:
      Depth_Datum_Name: North American Vertical Datum of 1988
      Depth_Resolution: 1
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Attribute values

  7. How does the data set describe geographic features?

    Nahant_CCB_sedcover
    Sediment Cover shapefile for Nahant to northern Cape Cod Bay, MA (Source: U.S. Geological Survey)

    FID
    Internal feature number. (Source: Esri)

    Sequential unique whole numbers that are automatically generated.

    Shape
    Feature geometry. (Source: Esri)

    Coordinates defining the features.

    sed_type
    Bottom-type classification based on twelve composite units that represent combinations of four end-member units (R= rock; G= gravel; S= sand; M= mud). (Source: Barnhardt and others (1998))

    ValueDefinition
    RgThe dominant texture (> 50%) Rock (R) is given the upper case letter and the subordinate texture (< 50%) gravel (g) is given a lower case letter.
    GrThe dominant texture (> 50%) Gravel (G) is given the upper case letter and the subordinate texture (< 50%) rock (r) is given a lower case letter.
    GsThe dominant texture (> 50%) Gravel (G) is given the upper case letter and the subordinate texture (< 50%) sand (s) is given a lower case letter.
    MThe end-member texture (~ 100%) Mud (M) is the primary texture.
    MsThe dominant texture (> 50%) Mud (M) is given the upper case letter and the subordinate texture (< 50%) sand (s) is given a lower case letter.
    SThe end-member texture (~ 100%) Sand (S) is the primary texture.
    SgThe dominant texture (> 50%) Sand (S) is given the upper case letter and the subordinate texture (< 50%) gravel (g) is given a lower case letter.
    SmThe dominant texture (> 50%) Sand (S) is given the upper case letter and the subordinate texture (< 50%) mud (m) is given a lower case letter.
    RsThe dominant texture (> 50%) Rock (R) is given the upper case letter and the subordinate texture (< 50%) sand (s) is given a lower case letter.
    SrThe dominant texture (> 50%) Sand (S) is given the upper case letter and the subordinate texture (< 50%) rock (r) is given a lower case letter.
    MgThe dominant texture (> 50%) Mud (M) is given the upper case letter and the subordinate texture (< 50%) gravel (g) is given a lower case letter.
    GThe end-member texture (~ 100%) Gravel (G) is the primary texture.
    N/AThere was not enough source input data to define sediment texture within this area.

    shep_code
    sediment nomenclature based on sand-silt-clay ratios defined in the CZM sample database (Source: Shepard (1954))

    ValueDefinition
    sandSediment whose main phase is <2 mm, but >0.062 mm
    gravelSediment whose main phase (usually >50%) is >2 mm
    sandy siltSediment whose main phase is silt, but with significant sand
    solidSediment whose main phase is rock, cobble, or boulder
    silty sandSediment whose main phase is sand, but with significant silt
    siltSediment whose main phase (usually >50%) is < 0.062 mm
    N/AThere was not enough source input data to define sediment texture within this area.
    gravelly sedimentediment whose main phase is >2 mm, but with significant other sediment.
    clayey siltSediment whose main phase is silt, but with significant clay.

    simple
    sediment nomenclature based on 3 simple classes: sand, mud, hardbottom as defined in the CZM sample database (Source: U.S. Geological Survey)

    ValueDefinition
    sandSediment whose primary component (> 50%) is sand
    hardbottomSediment whose primary component is rock, boulder, cobble, or coarse gravel
    mudSediment whose primary component (> 50%) is silt and clay
    N/AThere was not enough source input data to define simple sediment texture within this area.

    bedforms
    text field that describes the presence or absence of bedforms on the sea floor based on geophysical raster data (Source: U.S. Geological Survey)

    ValueDefinition
    yesbedforms are present within some part of the traced polygon in the source acoustic data
    N/Abedforms are not present within any part of the traced polygon in the source acoustic data

    phi_class
    Sediment class as defined by Wentworth classification determined using labratory analyzed samples in the CZM sample database (Source: Wentworth (1922))

    ValueDefinition
    coarse pebblessediment class whose phi size is between -4 and -5
    coarse siltsediment class whose phi size is between 4 and 5
    coarse sandsediment class whose phi size is between 0 and 1
    cobblesediment class whose phi size is between -6 and -8
    fine pebblessediment class whose phi size is between -2 and -3
    fine sandsediment class whose phi size is between 2 and 3
    fine siltsediment class whose phi size is between 6 and 7
    granulessediment class whose phi size is between -1 and -2
    medium pebblessediment class whose phi size is between -3 and -4
    medium sandsediment class whose phi size is between 2 and 1
    medium siltsediment class whose phi size is between 5 and 6
    solidsediment class whose phi size could not be determined from grain size data, but was determined to be rock based on acoustic data
    very coarse pebblessediment class whose phi size is between -5 and -6
    very coarse sandsediment class whose phi size is between 0 and -1
    very fine sandsediment class whose phi size is between 3 and 4
    very fine siltsediment class whose phi size is between 7 and 8
    N/Asediment class whose phi size could not be determined from grain size data or there were no samples with laboratory analyzed grain size statistics within the polygon

    Data_confi
    Each interpreted polygon was assigned a data interpretation confidence value from 1-4 based on the quality and number of input data sources. (Source: U.S. Geological Survey)

    ValueDefinition
    1Sediment texture regions that were defined based on the highest resolution bathymetry (5m) and backscatter (1m), bottom photos, sediment samples, and seismic interpretations were given the highest data interpretation confidence value of 1.
    2Areas where sediment texture was defined based on bathymetry of 30m resolution, backscatter of 1m resolution, bottom photos, and sediment samples were given an interpretation confidence value of 2.
    3A confidence value of 3 was given to areas with multibeam bathymetric and backscatter resolution of 10m and sediment samples, but no bottom photos or high density seismic interpretations were available.
    4The lowest confidence values (4) were given to areas where only lidar data at 2.5m resolution (and near full coverage) and sediment samples were available.
    0no cofidence in interpretation because there was not enough source data to make an interpretation

    Count_
    The number of sediment samples (with laboratory analyzed grain size statistics) that occur within each qualitatively-derived polygon. This field is automatically generated by Esri when point data (sample database) is joined to a polygon (sediment texture interpretation). (Source: Esri)

    Range of values
    Minimum:0
    Maximum:85
    Units:count
    Resolution:1

    Avg_GRAVEL
    Average percent weight (%) gravel (as determined from samples with laboratory analyzed grain size statistics) within each qualitatively derived polygon. This field was automatically generated by Esri as a summary of the numeric attributes of the points that fall inside a polygon when point data (sample database) is joined to a polygon (sediment texture interpretation). -999 is a no data value (Source: U.S. Geological Survey)

    Range of values
    Minimum:0
    Maximum:89.9
    Units:percent
    Resolution:0.1

    Avg_SAND
    Average percent weight (%) sand (as determined from samples with laboratory analyzed grain size statistics) within each qualitatively derived polygon. This field was automatically generated by Esri as a summary of the numeric attributes of the points that fall inside a polygon when point data (sample database) is joined to a polygon (sediment texture interpretation). -999 is a no data value (Source: U.S. Geological Survey)

    Range of values
    Minimum:1.79
    Maximum:100
    Units:percent
    Resolution:0.01

    Avg_SILT
    Average percent weight (%) silt (as determined from samples with laboratory analyzed grain size statistics) within each qualitatively derived polygon. This field was automatically generated by Esri as a summary of the numeric attributes of the points that fall inside a polygon when point data (sample database) is joined to a polygon (sediment texture interpretation). -999 is a no data value (Source: U.S. Geological Survey)

    Range of values
    Minimum:0
    Maximum:68.37
    Units:percent
    Resolution:0.1

    Avg_CLAY
    Average percent weight (%) clay (as determined from samples with laboratory analyzed grain size statistics) within each qualitatively derived polygon. This field was automatically generated by Esri as a summary of the numeric attributes of the points that fall inside a polygon when point data (sample database) is joined to a polygon (sediment texture interpretation). -999 is a no data value (Source: U.S. Geological Survey)

    Range of values
    Minimum:0
    Maximum:44.98
    Units:percent
    Resolution:0.1

    Avg_PHI
    Average phi size within each qualitatively derived polygon (-999 is a no data value, which means there were no samples with laboratory analyzed grain size statistics within that polygon) (Source: U.S. Geological Survey)

    Range of values
    Minimum:-4.07
    Maximum:7.83
    Units:phi
    Resolution:0.01

    mean_depth
    Average water depth within each qualitatively derived polygon. (Source: U.S. Geological Survey)

    Range of values
    Minimum:-61.15
    Maximum:-0.07
    Units:meters
    Resolution:0.01

    Shape_Leng
    Length of feature in meters. (Source: Esri)

    Range of values
    Minimum:125.941
    Maximum:144652.135
    Units:meters
    Resolution:0.001

    Shape_Area
    Area of feature in meters squared. (Source: Esri)

    Range of values
    Minimum:899.009
    Maximum:208403761.365
    Units:meters squared
    Resolution:0.001

    Positive real numbers that are automatically generated.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    U.S. Geological Survey
    Woods Hole, MA 02543-1598
    USA

    508-548-8700 x2259 (voice)
    508-457-2310 (FAX)
    ependleton@usgs.gov

Why was the data set created?

These sea floor sediment cover data were created from geophysical and sample data collected from Nahant to Northern Cape Cod Bay, and are used to characterize the sea floor in the area. Sediment type and distribution maps are important data layers for marine resource managers charged with protecting fish habitat, delineating marine boundaries, and assessing environmental change due to natural or human impacts.

How was the data set created?

  1. From what previous works were the data drawn?

    Ackerman and others, 2006 (source 1 of 7)
    Ackerman, S.D., Butman, B., Barnhardt, W.A., Danforth, W.W., and Crocker, J.M., 2006, High-resolution Geologic Mapping of the Inner Continental Shelf: Boston Harbor and Approaches, Massachusetts: Open-File Report 2006-1008, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    This report provided the source geophysical (sidescan and bathymetry) and bottom photograph data for the Boston Harbor and approaches region. These geophysical data were acquired between 2000 and 2001 by NOAA aboard the Ship Whiting and its launches. The sample data were collected in 2004 by the USGS and CZM. The NOAA cruises acquired sidescan-sonar and single-beam and multibeam bathymetric data. Sidescan data were collected with the Edgetech 272-T (100 kHz) or the Klein T-5500 (455 kHz) sonar. A hull-mounted RESON SeaBat 8101(240 kHz) was used to acquire the multibeam echosounder data. Single-beam echosounder data were acquired with an Odom Echotrac DF3200 MKII (100kHz). The USGS/CZM sampling cruise was conducted aboard the R/V Rafael using the mini SEABOSS and a VanVeen grab sampler. This report also provided a qualitative interpretation of the sidescan, bathymetry, and sample data collected in the region. These interpretive polygons were used as the initial interpretation for the Boston Harbor region. Some boundaries were slightly modified and field editing was conducted to match the classification scheme used in this study. These data also provided a good check for consistency in data interpretation.

    Andrews and others, 2010 (source 2 of 7)
    Andrews, B.D., Ackerman, S.D., Baldwin, W.E., and Barnhardt, W.A., 2010, Geophysical and Sampling Data from the Inner Continental Shelf: Northern Cape Cod Bay, Massachusetts: Open-File Report 2010-1006, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    This report provided the source geophysical (sidescan, bathymetry, and seismic-reflection profiles) and bottom photograph data for the Northern Cape Cod Bay region. These data were acquired between 2006 and 2008 by the USGS and CZM aboard the R/V Megan T. Miller, R/V Rafael, and R/V Connecticut. Bathymetric data were acquired using a Systems Engineering & Assessment, Ltd. (SEA) SWATHplus interferometric sonar system (234 or 117 kHz). Sidescan-sonar data were collected with a Klein 3000 dual-frequency sidescan-sonar (132/445 kHz), or a SWATHplus interferometric (117-kHz). Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (FM swept frequency 0.5-12 kHz). Sediment samples and bottom photos were collected with a modified Van Veen grab sampler and SEABOSS, respectively.

    Barnhardt and others, 2010 (source 3 of 7)
    Barnhardt, W.A., Ackerman, S.D., Andrews, B.D., and Baldwin, W.E., 2010, Geophysical and Sampling Data from the Inner Continental Shelf: Duxbury to Hull, Massachusetts: Open-File Report 2009-1072, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    This report provided the source geophysical (sidescan, bathymetry, and seismic-reflection profiles) and bottom photograph data for the Duxbury to Hull, MA region. These data were acquired between 2006 and 2007 by the USGS, CZM, and NOAA aboard the R/V Megan T. Miller, R/V Rafael, R/V Connecticut, and NOAA launches 1005 and 1014. USGS bathymetric data were acquired using a Systems Engineering & Assessment, Ltd. (SEA) SWATHplus interferometric sonar system (234 or 117 kHz). NOAA bathymetric and backscatter data were acquired with a hull-mounted RESON SeaBat 3101 and 8125. USGS sidescan-sonar data were collected with a Klein 3000 dual-frequency sidescan-sonar (132/445 kHz), or a SWATHplus interferometric (117-kHz). USGS chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (FM swept frequency 0.5-12 kHz). Sediment samples and bottom photos were collected with a modified Van Veen grab sampler and SEABOSS, respectively.

    Butman and others, 2007 (source 4 of 7)
    Butman, B., Valentine, P.C., Middleton, T.J., and Danforth, W.W., 2007, A GIS Library of Multibeam Data for Massachusetts Bay and the Stellwagen Bank National Marine Sanctuary, Offshore of Boston, Massachusetts: Digital Data Series 99, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    This report provided the source geophysical data (sidescan and bathymetry) for the western Massachusetts Bay region including Stellwagen Bank. These data were acquired between 1994 and 1998 by the USGS, Canadian Hydrographic Survey, and University of New Brunswick aboard the Frederick G. Creed. Bathymetric and backscatter data were acquired using Simrad Subsea EM 1000 Multibeam Echo Sounder.

    CZM sample database (source 5 of 7)
    Ford, K.H., Huntley, E.C., Sampson, D.W., and Voss, S., Unpublished Material, Massachusetts Sediment Database:,.

    Other_Citation_Details:
    This sample database has been compiled and vetted from existing samples and datasets by the Massachusetts Office of Coastal Zone Management. The data are currently unpublished, but may be acquired by contacting the CZM office: 251 Causeway St Boston, MA 02114 (617) 626-1000 czm@state.ma.us
    Type_of_Source_Media: digital vector
    Source_Contribution:
    Sediment sample databases of Ford and Voss (2010) and McMullen and others (2011) were combined then edited and supplemented with NOAA chart sampling data and over 2,000 bottom photos and descriptions at more than 400 stations by a group of GIS specialists at the Massachusetts Office of Coastal Zone Management (Emily Huntley, personal communication). These data contained sediment laboratory statistics when available, visual descriptions if sediment analysis was not perfromed or if the site was a bottom photograph, and classification fields of Barnhardt and others (1998), Shepard (1954), and Wentworth (1922) as well as average sediment statistics and phi size, when laboratory analysis was conducted.

    USACE- JALBTCX, 2008 (source 6 of 7)
    U.S. Army Corps of Engineers, Joint Airborne LiDAR Bathymetry Center of Expertise, 2008, Massachusetts LiDAR Grid Data in Coastal Areas: Fugro Pelagos, Inc, San Diego, CA.

    Type_of_Source_Media: disc
    Source_Contribution:
    This report provided the source lidar data for the very nearshore (< -5 m) region. Lidar (Light Detection and Ranging) data were acquired with a SHOALS-1000T (for hydrographic & topographic data) using the Joint Airborne LiDAR Bathymetry Center of Expertise (JALBTCX) lidar plane.

    Poppe and others, 2006 (source 7 of 7)
    Poppe, L.J., Paskevich, V.F., Butman, B., Ackerman, S.D., Danforth, W.W., Foster, D.S., and Blackwood, D.S., 2006, Geological Interpretation of Bathymetric and Backscatter Imagery: Open-File Report 2005-1048, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    This report provided the source geophysical data (sidescan and bathymetry) for the Outer Cape Cod region. These data were acquired in 1998 by the USGS, Canadian Hydrographic Survey, and University of New Brunswick aboard the Frederick G. Creed. Bathymetric and backscatter data were acquired using Simrad Subsea EM 1000 Multibeam Echo Sounder.

  2. How were the data generated, processed, and modified?

    Date: 14-Feb-2012 (process 1 of 3)
    The texture and spatial distribution of Seafloor sediment were qualitatively-analyzed in ArcGIS using several input data sources (listed in the source contribution), including acoustic backscatter, bathymetry, Lidar, seismic-reflection profile interpretations, bottom photographs, and sediment samples. In order to create the interpretation, first a polygon shapefile of the study area was created (with ArcMap version 9.3.1) and merged with the published Boston Harbor interpretive polygons (Ackerman and others, 2006). Then sediment texture polygons were created using 'cut polygon' and 'auto-complete polygon' in an edit session. In general, polygon editing was done at scales between 1:8,000 and 1:20,000, depending on the size of the traced feature and the resolution of the source data. The following numbered steps outline the workflow of the data interpretation.
    1. Backscatter intensity data (available at 1 to 10 m resolutions) was the first input. Changes in backscatter amplitude were digitized to outline possible changes in seafloor texture based on acoustic return. Areas of high backscatter (light colors) have strong acoustic reflections and suggests boulders, gravels, and generally coarse seafloor sediments. Low-backscatter areas (dark colors) have weak acoustic reflections and are generally characterized by finer grained material such as muds and fine sands. 2. The polygons were then refined and edited using gradient, rugosity, and hillshaded relief images derived from interferometric and multibeam swath bathymetry and Lidar (available at 2.5 - 30 m resolutions). Areas of rough topography and high rugosity are typically associated with rocky areas, while smooth, low-rugosity regions tend to be blanketed by fine-grained sediment. These bathymetric derivatives helped to refine polygon boundaries where changes from primarily rock to primarily gravel may not have been apparent in backscatter data, but could easily be identified in hillshaded relief and slope changes. 3. The third data input (where available) was the stratigraphic interpretation of seismic-reflection profiles, which further constrained the extent and general shape of seafloor sediment distributions and rocky outcrops, and also provided insight concerning the likely sediment texture of the feature based on the pre-Quaternary, glacial or post-glacial origin. Seismic lines and the surficial geologic maps derived from them and used here as input data were collected at typically 100-meter spacing, with tie-lines generally spaced 1-km apart. 4. After all the seafloor features were traced from the geophysical data, new fields were created in the shapefile called 'sed_type' and 'shep_code'. Bottom photographs and sediment samples were used to define sediment texture for the polygons using Barnhardt and others (1998) and Shephard code (Shepard, 1954) classifications. Some polygons had more than one sample, and some polygons lacked sample information. For multiple samples within a polygon, the dominant sediment texture (or average phi size) was used to classify sediment type (often aided by the 'data join' sediment statistics described in a later processing step). In rocky areas, bottom photos were used in the absence of sediment samples to qualitatively define sediment texture. Polygons that lacked sample information were texturally defined through extrapolation from adjacent or proximal polygons of similar acoustic character that did contain sediment samples. 615 samples of the over 5,500 total within the study area were analyzed in the laboratory for grain size. Samples with laboratory grain size analysis were preferred over visual descriptions when defining sediment texture throughout the study area. Bottom photos are typically around 2-km apart, and the density of sediment samples varies throughout the study area, with Boston Harbor having a high density of samples, while rocky areas have almost no sediment samples.

    Person who carried out this activity:

    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    U.S. Geological Survey
    Woods Hole, MA 02543-1598
    USA

    508-548-8700 x2259 (voice)
    508-457-2310 (FAX)
    ependleton@usgs.gov

    Date: 12-Apr-2012 (process 2 of 3)
    After some additional qualitative polygon editing and reshaping was done in order to create a sediment map that was in the best agreement with all input data: lidar, bathymetry, backscatter, seismic interpretations, bottom photographs, and sediment samples, 4 more fields were added (ArcMap version 9.3.1). The first field, 'simple' is just 3 classes: sand, mud, or hardbottom. Another field 'bedforms' defines the presence or absence of bedforms features in the geophysical data, which helps determine seabed mobility. Another filed 'phi_class' was created and defined using the Wentworth (1922) sediment classification, and finally, a field 'Data_confi' was added as a data interpretation confidence, which describes how confident we are in the interpretation based on the number and quality of the input data sources (see the entity and attribute sections for more information on these fields). The remaining fields contain sediment texture statistics or mean water depth information and were created and populated using data joins or zonal statistics functions within ArcMap (version 9.3.1). The fields beginning with "Avg_" and the "Count_" field were automatically generated by computing a data join where the CZM sample database (vector points) was edited to include only the samples with laboratory sediment analysis and joined to the qualitatively-derived polygon file. Each polygon was given an average of the numeric attributes of the points (with laboratory grain size analysis) that fall inside it, and the count field shows how many laboratory analyzed points fall inside it. 615 samples were analyzed in the laboratory. Several fields that were not wanted were deleted after the join. Finally, a mean water depth field was created using zonal statistics, where the mean water depth for each polygon was derived from the topographic and bathymetric grid (<http://pubs.usgs.gov/of/2012/1157/GIS_catalog/SourceData/bathy/>).

    Person who carried out this activity:

    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    U.S. Geological Survey
    Woods Hole, MA 02543-1598
    USA

    508-548-8700 x2259 (voice)
    508-457-2310 (FAX)
    ependleton@usgs.gov

    Date: 12-May-2012 (process 3 of 3)
    Finally, a feature dataset was generated inside a geodatabase (ArcCatalog version 9.3.1), and new topology rules were established to make sure that there were no overlapping polygons or accidental gaps between adjacent polygons. The topology error inspector (ArcMap version 9.3.1) was used to find topology errors and fix them. Overlapping polygon errors were fixed, and several gaps were marked as exceptions since there are several islands and significant data gaps within the study area. Very small (less than 1-square meter) gaps and triangular jogs in polygon boundaries within Boston Harbor exist where data published by Ackerman and others (2006) was used. These small topology feature errors were not corrected. Length and Area fields were generated automatically for all polygons in the geodatabase. The data were then exported to a shapefile and the polygons were reprojected from UTM Zone 19N, WGS84 to GCS WGS84.

    Person who carried out this activity:

    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598
    USA

    (508)-548-8700 x2259 (voice)
    (508)-457-2310 (FAX)
    ependleton@usgs.gov

  3. What similar or related data should the user be aware of?

    Kelley, J.T., Barnhardt, W.A., Belknap, D.F., Dickson, S.M., and Kelley, A.R., 1996, The Seafloor Revealed: The Geology of the Northwestern Gulf of Maine Inner Continental Shelf: Maine Geological Survey Open-File Report 96-6, Maine Geological Survey, Natural Resources Information and Mapping Center, Augusta, Maine.

    Shepard, F.P., 1954, Nomenclature Based on Sand-Silt-Clay Ratios: Journal Sedimentary Petrology volume 24, Society for Sedimentary Geology, Tulsa, OK.

    Barnhardt, W.A., Kelley, J.T., Dickson, S.M., and Belknap, D.F., 1998, Mapping the Gulf of Maine with Side-scan Sonar: a New Bottom-type Classification for Complex Seafloors: Journal of Coastal Research volume 14(2), Coastal Education and Research Foundation, Inc., Royal Palm Beach, FL.

    Wentworth, C.K., 1922, A Scale of Grade and Class Terms for Clastic Sediments: Journal of Geology vol. 30, University of Chicago Press, Chicago, IL.

    McMullen, K.Y, Paskevich, V.F., and Poppe, L.J., 2011, USGS East-coast Sediment Analysis: Procedures, Database, and GIS Data: Open File Report 2005-1001, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Ford, K.H., and Voss, S.E., 2010, Seafloor Sediment Composition in Massachusetts Determined Using Point Data: Massachusetts Division of Marine Fisheries Technical Report TR-45, Massachusetts Division of Marine Fisheries, New Bedford, MA.

    Online Links:

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?

    These data were produced qualitatively from acoustic and sample data with varying resolutions. Horizontal uncertainty associated with sample collection especially, can be quite high (100's of meters), much higher than positional uncertainty associated with acoustic data (usually less than <10's of meters). The date of sample collection and ship station positioning all contribute to sample position uncertainty. These qualitatively derived polygons outlining sea floor features are estimated to be within 50 meters, horizontally, but locally may be higher when sediment texture delineation is based on sample information alone.

  3. How accurate are the heights or depths?

    Although there is a field for mean water depth, there is no assumption of vertical accuracy. The depth value is an average of all grid cells (<http://pubs.usgs.gov/of/2012/1157/GIS_catalog/SourceData/bathy/>) within each polygon. In many cases the mean depth value covers a range of depths from near zero to < -20 meters, and as such should not be used for navigation or taken as an absolute depth value within a polygon.

  4. Where are the gaps in the data? What is missing?

    These sediment cover data are defined for areas where source data exists. In general, gaps in the coverage coincide with gaps in the source data. However, some small data gaps were interpreted through extrapolation. Areas of lower data quality and incomplete coverage are noted in a data confidence attribute field.

  5. How consistent are the relationships among the observations, including topology?

    These data were drawn and vetted for accuracy using the source input rasters and point sample data described in the processing steps and source contributions. Qualitatively-defined polygons for the Boston Harbor and approaches region had already been drawn and published by Ackerman and others (2006). In their study, their region of interest was defined by using a 'convert raster to feature' function on sidescan sonar imagery within ArcGIS. This conversion task created several very small (~ 1 square-meter) triangular and rectilinear-shaped gaps along the boundaries of the defined polygons within Boston Harbor. The original Ackerman and other (2006) bottom type polygons were merged with the polygons created in this study, and polygon and field editing was done in order to make them fit the classification schemes used in this report. However, the very small topology errors associated with the original data have not been removed, primarily because they are well below the intended scale of application of these data (1:25,000). Overlapping features and unintentional gaps within the rest of the survey area were identified using the topology checker in ArcMap (version 9.3.1) and corrected or removed.

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:
Not to be used for navigation. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information. Additionally, there are limitations associated with qualitative sediment mapping interpretations. Because of the scale of the source geophysical data and the spacing of samples, not all changes in sea floor texture are captured. The data were mapped between 1:8,000 and 1:25,000, but the recommended scale for application of these data is 1:25,000. Features below 5,000 m2 or less than 50 m wide were not digitized due to positional uncertainty, lack of sample information, and the often ephemeral nature of small-scale sea floor features. Not all digitized sea floor features contained sample information, so often the sea floor texture is characterized by the nearest similar feature that contains a sample. Conversely, sometimes a digitized feature contained multiple samples and not all of the samples within the feature were in agreement (of the same texture). In these cases the dominant sediment texture was chosen to represent the primary texture for the polygon. Samples from rocky areas often only consist of bottom photographs, because large particle size often prevents the recovery of a sediment sample. Bottom photo classification can be subjective, such that determining the sediment type that is greater than 50% of the view frame is estimated by the interpreter and may differ among interpreters. Bottom photo transects often reveal changes in the sea floor over distances of less than 100 m and these changes are often not observable in acoustic data. Heterogeneous sea floor texture can change very quickly, and many small-scale changes will not be detectable or mappable at a scale of 1:25,000. The boundaries of polygons are often inferred based on sediment samples, and even boundaries that are traced based on amplitude changes in geophysical data are subject to migration. Polygon boundaries should be considered an approximation of the location of a change in texture.

  1. Who distributes the data set? (Distributor 1 of 1)

    Elizabeth A Pendleton
    U.S. Geological Survey
    Geologist
    U.S. Geological Survey
    Woods Hole, MA 02543-1598
    USA

    508-548-8700 x2259 (voice)
    508-457-2310 (FAX)
    ependleton@usgs.gov

  2. What's the catalog number I need to order this data set?

    Downloadable Data

  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 U.S. Geological Survey 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.

  4. How can I download or order the data?

  5. What hardware or software do I need in order to use the data set?

    These data are available in Environmental Systems Research Institute (Esri) shapefile format. The user must have software capable of importing and processing this data type.

Who wrote the metadata?

Dates:
Last modified: 02-Jul-2013
Metadata author:
Elizabeth A. Pendleton
U.S. Geological Survey
Geologist
U.S. Geological Survey
Woods Hole, MA 02543-1598
USA

508-548-8700 x2259 (voice)
508-457-2310 (FAX)
ependleton@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.21 on Tue Jul 02 13:39:32 2013