ei_2hm_nofill - uninterpolated swath bathymetry collected by the U.S. Geological Survey - Woods Hole Coastal and Marine Science Center surrounding the nearshore of the Elizabeth Islands, MA, 2010 (ESRI grd)

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Frequently-anticipated questions:

What does this data set describe?

Title:
ei_2hm_nofill - uninterpolated swath bathymetry collected by the U.S. Geological Survey - Woods Hole Coastal and Marine Science Center surrounding the nearshore of the Elizabeth Islands, MA, 2010 (ESRI grd)
Abstract:
These data were collected under a cooperative agreement between the Massachusetts Office of Coastal Zone Management (CZM) and the U.S. Geological Survey (USGS), Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center (WHCMSC). 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 due to natural or human impacts. The project is focused on the inshore waters of coastal Massachusetts, primarily in water depths of 2-30 meters. Data collected for the mapping cooperative 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 data collected in this study area located around the western extent of the Elizabeth Islands includes high resolution bathymetry, acoustic-backscatter intensity, seismic-reflection, and navigation data. These data were collected during a nearshore cruise in September 2010 onboard the R/V Rafael using the following equipment: an SEA Ltd SwathPlus interferometric sonar (234 kHz), Klein 3000 dual frequency sidescan sonar, an Edgetech 424 chirp subbottom profiling system, and 4 GPS antennae. More information about the cruise conducted as part of the project: Geologic Mapping of the Seafloor Offshore of Massachusetts can be found on the Woods Hole Coastal and Marine Science Center Field Activity webpage: <http://quashnet.er.usgs.gov/data/2010/10003/>
  1. How should this data set be cited?

    U.S. Geological Survey, 2012, ei_2hm_nofill - uninterpolated swath bathymetry collected by the U.S. Geological Survey - Woods Hole Coastal and Marine Science Center surrounding the nearshore of the Elizabeth Islands, MA, 2010 (ESRI grd): Open-File Report 2011-1184, 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, Elizabeth A. , Twichell, David C. , Foster, David S. , Worley, Charles R. , Irwin, Barry J. , and Danforth, William W. , 2012, High-Resolution Geophysical Data From the Sea Floor Surrounding the Western Elizabeth Islands, Massachusetts: Open-File Report 2011-1184, 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: -70.995552
    East_Bounding_Coordinate: -70.847928
    North_Bounding_Coordinate: 41.462328
    South_Bounding_Coordinate: 41.388012

  3. What does it look like?

    <https://pubs.usgs.gov/of/2011/1184/GIS_catalog/bathy/bathy_nofill.png> (PNG)
    Woods Hole Coastal and Marine Science Center Swath interferometric bathymetry surrounding the nearshore of the Elizabeth Islands, MA

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

    Beginning_Date: 10-Sep-2010
    Ending_Date: 16-Sep-2010
    Currentness_Reference: Data were not collected on 20100915 due to weather conditions.

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: raster digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Raster data set. It contains the following raster data types:

      • Dimensions 3194 x 4866 x 1, type Grid Cell

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

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 19
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -69.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 2.500000
      Ordinates (y-coordinates) are specified to the nearest 2.500000
      Planar coordinates are specified in meters

      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:
      Depth_System_Definition:
      Depth_Datum_Name: Mean lower low water
      Depth_Resolution: 0.1 meters
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Implicit coordinate

  7. How does the data set describe geographic features?

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?

    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov

Why was the data set created?

This grid represents approximately 24.5 square km of bathymetric data that were collected in 2010. These data are used to define the sea-floor morphology surrounding the nearshore of the western Elizabeth Islands, Massachusetts. This uninterpolated grid provides a representation of the seafloor as it was collected with data gaps left as NoData values.

How was the data set created?

  1. From what previous works were the data drawn?

    (source 1 of 1)
    U.S. Geological Survey.

    Type_of_Source_Media: disc
    Source_Contribution:
    Swath data acquisition at sea (2010): These bathymetric data were collected with a 234 kHz SEA Ltd Swathplus interferometric sonar mounted on the bow of the R/V Rafael of Woods Hole, MA. Data were acquired between Sept. 10, 2010 and Sept. 16, 2010. All data were acquired with SwathPlus Software (version: 3.7.0). Tracklines are spaced 100 m apart in the shore parallel direction.

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

    Date: 2010 (process 1 of 4)
    SwathPlus Software (version: 3.7.0) was used to acquire the raw swath data (*.sxr) and output a processed soundings file (*.sxp). Several bathy filters were applied to the processed file within SwathPlus to remove erroneous soundings and reduce the density of the data. Corrections were also applied for speed of sound changes (using sound velocity profiles), ship motion, GPS antennae offsets, and transducer depth and angle below the surface. Bathy filters included a low amplitude (100%), range (1-m below the surface), box (2-m to avoid nadir), alongtrack 1 (depth difference of 10-m, window size 10-m, and learn rate of 0.6), alongtrack 2 (depth difference of 1-m, window size 1-m, and learn rate of 0.9), and a mean filter (0.1-m).Several lines (l91f1-l100f1) were in very shallow water between Nashawena and Cuttyhunk. The filters used above for the majority of the survey were not tracking the seafloor well in very shallow water. All filters except the low amplitude and mean filter were turned off for these shallow water lines, to allow more data into the processed file. This procedure resulted in more editing later in CARIS, but it preserved more good data as well.

    Person who carried out this activity:

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

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

    Date: 2010 (process 2 of 4)
    CARIS (version: HIPS and SIPS 7.0; service pack 2) was used to further process, finalize, and create a surface from the bathy files (*.sxp) from SwathPlus. CARIS processing with HIPS (hydrographic information processing system) has a workflow that ensures the user has done all necessary corrections to the soundings before creating a final gridded surface. The workflow starts with creating a vessel file (the R/V Rafael for this cruise). The vessel file contains any information related to GPS, MRU, and water level offsets that weren't included during acquisition using SwathPlus. Additionally, the user can report any errors in offsets (i.e. MRU to transducer measurement error, usually around 1-2 cm), which will later be used to calculate TPU (total propagated uncertainty), which is a requirement for CUBE (Combined Uncertainty and Bathymetry Estimator) editing (Calder, 2003). The next steps in the HIPS workflow include creating a project and converting the *.sxp data to CARIS HDCS (hydrographic cesar) format. Sound velocity corrections are the next step in data processing. Errors in soundings due to additional sound refraction not accounted for by sound velocity profiles were done using the CARIS refraction editor. These artifacts can be recognized in a cross-swath profile of a relatively flat patch of sea floor. When viewing the swath data across a profile, the sea floor will appear to have a "frown" or "smile" when in fact the data should be flat across the profile. Insufficient and/or erroneous sound velocity information results in an under or over-estimate of water depth, which increases with distance from the center of the swath. Next a tide correction was applied in CARIS (described in the next process step) and merged with the soundings, and then the TPU was calculated in order to utilize the CUBE editor, which is an uncertainty based data cleaning tool that creates a 'best estimate' surface for the soundings. The cube surface is then used to further QC the soundings. Some lines required swath editing or subset editing as well as automated filtering, especially in the shallow water areas (l91f1-l100f1). The final step in the workflow was to finalize the surface (at 2.5 m resolution) and export it from CARIS in XYZ format, which can then be imported to other programs.

    Person who carried out this activity:

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

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

    Date: 2010 (process 3 of 4)
    In order to apply a tidal correction to the soundings, an offset from Mean Sea Level MSL) to Mean Lower Low Water (MLLW) (-0.676 m) was entered into the HYPACK configuration file for the RTK device (dev 0) setup prior to the survey. This value was calculated by setting a DGPS antenna on a number of survey stations around Buzzard's Bay and using the bench mark sheets in conjunction with the DGPS height calculations to determine the offset from MLLW to MSL. Calculated HYPACK RTK water level heights were then extracted from the raw HYPACK files using an AWK script (parseNovatelHypackTides.awk), which calculates the MLLW tide value for each Julian day of the survey. An offset of 2.9 meters was added to each calculated tide value (TID 0) to compensate for the RTK antenna to water line offset, and then the sign was inverted. Since HYPACK reports water level heights relative to MLLW, heights above the MLLW datum are reported as negative values because they are above the datum per standard surveying XYZ convention. The file resulting from running the AWK script produces a file of MLLW tidal height corrections formatted in the CARIS TID file format: YYYY/MM/DD HH:MM 0.00 where 0.00 is the correct water level height. The RTK heights were then merged into the processed CARIS depth soundings in the bathy processing workflow using the Tide load and Merge functions.

    Person who carried out this activity:

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

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

    Date: 05-Apr-2011 (process 4 of 4)
    The 2.5 meter tide corrected base surface that was finalized and exported from CARIS was gridded in ArcMap (version 9.3) using Spatial Analyst-- convert features to raster. An output cell-size of 2.5 meters was used, and NoData values were left uninterpolated for this surface. The 2.5 meter tide corrected base surface that was finalized and exported from CARIS was gridded in ArcMap using 3D Analyst - natural neighbors. A shapefile polygon representing the survey boundary was used to clip the grid to the extent of the data.

    Person who carried out this activity:

    Elizabeth 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?

    Calder, B.R., 2003, Automatic Statistical Processing of Multibeam Echosounder Data: International Hydrographic Review Volume 4, INT HYDROGRAPHIC BUREAU, The Netherlands.

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 navigation for these data was acquired with a Coda Octopus F180 Differential Global Positioning System + Wide Area Augmentation System (DGPS+WAAS); they are accurate to + or - 1 to 2 meters, horizontally. All DGPS data are referenced to WGS84, and the horizontal distance between the pole-mounted interferometric sonar transducers, 0.5m below the sea surface, and the DGPS antennae located on the same pole on the bow of the R/V Rafeal, 2.5 m above the sea surface, are corrected.

  3. How accurate are the heights or depths?

    The theoretical vertical resolution of the SEA Ltd SwathPlus interferometric sonar is 1 % of water depth, approximately 0.03 to 0.25 m within the study area. An Octopus F180 Attitude and Positioning system was used to correct for vessel roll, pitch, heave, and yaw, which has a theoretical vertical accuracy of a few mm. Tidal offsets were corrected to MLLW using RTK GPS heights. Field tests using submerged targets suggest that the vertical accuracy of the RTK tidal correction is less than 30 cm. Gridding algorithms and cell sizes for these data could introduce errors as great as 3 m along the edges of the data. Gridding-induced errors are likely much smaller (< 0.2 m) for most of the study. Changes in ship draft due to water and fuel usage were not considered. Total vertical accuracy for these data are assumed to be + or - 50 cm.

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

    All the bathymetric data from cruise 2010-003-FA were used to generate this grid, however, l13f1 and l22f1 were corrupted during acquisition, so these lines are not complete. The generator shorted out causing write errors in the raw swath file.

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

    Any spurious data points were removed during processing.

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. The 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 originator of the dataset.

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

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

    (508) 548-8700x2259 (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 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.

  4. How can I download or order the data?

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

    The grid contained in the .zip file is available as an ESRI binary grid. To utilize this data, the user must have a GIS software package capable of reading an ESRI binary grid.

Who wrote the metadata?

Dates:
Last modified: 18-Nov-2011
Metadata author:
Elizabeth A. Pendleton
U.S. Geological Survey
Geologist
384 Woods Hole Road
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 2.8.25 on Fri Nov 18 14:46:13 2011