Bathymetric data collected in the Belfast Bay, Maine pockmark field using a SWATHplus-M interferometric sonar in 2006 and 2008, by the U.S. Geological Survey (32-bit floating point raster, UTM 19 WGS 84, MLLW)

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Frequently anticipated questions:

What does this data set describe?

Bathymetric data collected in the Belfast Bay, Maine pockmark field using a SWATHplus-M interferometric sonar in 2006 and 2008, by the U.S. Geological Survey (32-bit floating point raster, UTM 19 WGS 84, MLLW)
The U.S. Geological Survey, Woods Hole Coastal and Marine Science Center in cooperation with the University of Maine mapped approximately 50 square kilometers of the seafloor within Belfast Bay, Maine. Three geophysical surveys conducted in 2006, 2008 and 2009 collected swath bathymetric (2006 and 2008) and chirp seismic reflection profile data (2006 and 2009). The project characterized the spatial, morphological and subsurface variability of the Belfast Bay, Maine pockmark field. Pockmarks are large seafloor depressions that are associated with seabed fluid escape.
These data were collected during three separate surveys: Field Activity 2006-024-FA, 12-17 Sept, 2006 Field Activity 2008-024-FA, 17-24 Sept, 2008 Field Activity 2009-037-FA, 27-30 July, 2009
The EdgeTech 424 seismic system became inoperable at the beginning of survey 2008-024-FA, although the survey continued collecting interferometric and sidescan sonar data. The third survey in 2009 (2009-037-FA) was conducted to collect just seismic data that was not collected during 2008-024-FA.
  1. How might this data set be cited?
    U.S. Geological Survey, 20201210, Bathymetric data collected in the Belfast Bay, Maine pockmark field using a SWATHplus-M interferometric sonar in 2006 and 2008, by the U.S. Geological Survey (32-bit floating point raster, UTM 19 WGS 84, MLLW): data release DOI:10.5066/P90QQCOR, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

    Online Links:

    This is part of the following larger work.

    Andrews, Brian D., Danforth, William W., Brothers, Laura L., and Barnhardt, Walter A., 2020, High-resolution geophysical data collected in the Belfast Bay, Maine pockmark field in 2006, 2008, and 2009 by the U.S. Geological Survey: data release DOI:10.5066/P90QQCOR, U.S. Geological Survey, Reston, Virginia.

    Online Links:

    Suggested citation: Andrews, B.D., Danforth, W. W., Brothers, L.L., Barnhardt, W. A., 2020, High-resolution geophysical data collected in the Belfast Bay, Maine Pockmark Field in 2006, 2008, and 2009 by the U.S. Geological Survey: U.S. Geological Survey data release,
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -68.971634
    East_Bounding_Coordinate: -68.875830
    North_Bounding_Coordinate: 44.433091
    South_Bounding_Coordinate: 44.305996
  3. What does it look like? (JPG)
    Thumbnail image of bathymetry collected in Belfast Bay, Maine.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 12-Sep-2006
    Ending_Date: 27-Sep-2008
    Bathymetry data were collected on the following dates: 20060912-20060917 (Julian day 255-260); 20080924-20080927 (Julian day 261-268).
  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 2822 x 1524, type Pixel
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 19N
      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 5.000000
      Ordinates (y-coordinates) are specified to the nearest 5.000000
      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.
      Depth_Datum_Name: Mean lower low water
      Depth_Resolution: 0.1
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    The GeoTIFF is a 32-bit image where the pixel values represent depth in meters referenced to the mean lower low tidal datum. Depth range is between -2.72 and -87.46 meters.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
    Please recognize the U.S. Geological Survey (USGS) as the source of this information.
  3. To whom should users address questions about the data?
    Brian Andrews
    U.S. Geological Survey
    384 Woods Hole Rd.
    Woods Hole, MA

    508-548-8700 x2348 (voice)
    508-457-2310 (FAX)

Why was the data set created?

This bathymetric dataset was collected to understand the morphology of the pockmark field in Belfast Bay, Maine.

How was the data set created?

  1. From what previous works were the data drawn?
    SWATHplus-M echo sounder data (source 1 of 1)
    U.S. Geological Survey, Unpublished Material, raw SWATHplus-M data in .sxr format.

    Type_of_Source_Media: disc
    SONAR CONFIGURATION: Bathymetry data were collected using a Systems Engineering and Assessment Ltd. (SEA) SWATHplus-M interferometric sonar operating at a frequency of 234 kHz. The sonar transducers were mounted on a rigid pole installed on the bow of the RV Rafael and were deployed at a depth of 0.7m below the water line while collecting data. Typical sonar operating parameters include a transmit power of 9, transmit length of 28 cycles, 20148 samples per channel and a 100-meter range.
    A motion reference unit (TSS Ltd.) Dynamic Motion Sensor (DMS) was mounted directly above the transducers and continuously measured vertical displacement (heave), and attitude (pitch and roll) of the survey vessel during data acquisition. Data were recorded to SWATHplus-M raw format (*.sxr) using Swath Processor software. Sound-velocity profiles were collected approximately every 2 hours during the survey using a hand-casted Applied Microsystems SV Plus sound velocimeter. Real-time Kinematic Global Positioning System (RTK-GPS) navigation was used to determine the horizontal and vertical position (x,y,z) of the GPS antenna with sub-meter accuracy mounted on top of the pole. The RTK-DGPS coordinates were transmitted to the survey vessel from a land-based RTK-DGPS station established by the USGS over National Ocean Service (NOS) monument 5191-A Belfast, Penobscot Bay, Maine
  2. How were the data generated, processed, and modified?
    Date: Sep-2008 (process 1 of 4)
    Note: Processing steps 1-3 described here are the same for both of the surveys that collected bathymetry (2006-024-FA, and 2008-024-FA)the processing date reflects the most recent (2008) date. Depths were corrected to Mean Lower Low Water (MLLW) using 1 second RTK-GPS heights of the GPS antenna mounted over the SWATHplus-M sonar head. These heights were extracted from each HYPACK navigation file using the AWK script "doRTK1_by_line_FIX" and smoothed in MATLAB (version 7.20.232 R2006a) using a third order polynomial. The smoothed 1-second heights were averaged to 1-minute heights and formatted for use in CARIS HIPS using the AWK script "DoRTK2" to produce the file "TidesAllCARIS.tid" The contact person for this and all subsequent processing steps below is Brian Andrews. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Brian Andrews
    384 Woods Hole Rd.
    Woods Hole, MA

    508-548-8700 x2348 (voice)
    508-457-2310 (FAX)
    Date: Sep-2008 (process 2 of 4)
    Step 2. CONVERT SXR to SXP.
    Each raw SWATHplus-M bathymetric sonar file (sxr) was converted to a SWATHplus processed file (sxp) using SEA SWATHplus Swath Processor (ver. 3.5.19). During the conversion process, sound velocity profiles were used to minimize potential refraction artifacts from fluctuations in the speed of sound within the water column. Various bathymetric filters were applied to eliminate sounding outliers.
    Date: Sep-2008 (process 3 of 4)
    A new CARIS HIPS project (ver. 6.1) was created using the Universal Transverse Mercator (UTM) Zone 19, WGS 84 coordinate system. Each SWATHplus processed file (sxp) was imported to the new CARIS project using the Import/Conversion Wizard. A 5-meter resolution Bathymetric and Statistical Error (BASE) Surface was created from the files for each Julian day. The BASE surface for each day was reviewed for any inconsistencies or data anomalies. Navigation was edited as needed using the navigation editor tool in CARIS. Filters were applied to each line including beam to beam slopes and across track angle. The CARIS refraction editor was used to adjust the speed of sound in some cases to flatten out the depth profiles produced by localized variations in speed of sound through the water column.
    Date: Sep-2015 (process 4 of 4)
    A 5-m BASE surface of the entire survey area created using all the lines from 2006 and only the lines from 2008 that did not overlap with 2006 (Lines L43f1-L86f1).
    The final CARIS HIPS BASE (depth) surface was exported as a 32-bit floating point GeoTIFF (BelfastBay_SWATHplus_bathymetry_5m.tif) using the export context menu with in HIPS (v. 9.0.18).
  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    These data were navigated using Real-Time Kinematic Global Positioning System (RTK-GPS) which provides horizontal positional accuracies (x and y) on the decimeter scale. The SWATHplus transducers were mounted on a rigid pole from the bow of the R/V Rafael, approximately 0.5 below waterline. Position data were recorded by Hypack Software (v. 4.3).
  3. How accurate are the heights or depths?
    Based on SWATHplus-M interferometric sonar system specifications, vertical accuracy of the raw data may approximate 1% of water depth, which translates to 0.03 0.9 meters within the Belfast Bay survey area. RTK-GPS was used to establish water-level heights relative to Mean Lower Low Water (MLLW), providing decimeter-scale accuracies. Tide-correction was done in post-processing (see process steps). Refraction artifacts were minimized by acquiring a range of sound velocity profiles throughout the survey area to model the sound velocity structure of the water column. Changes in vessel draft due to fuel consumption was not considered.
  4. Where are the gaps in the data? What is missing?
    This grid does not include all the data from the tie lines in areas of overlap with main scheme lines. Survey lines collected in 2008 that overlap with lines collected in 2006 were intended for sonar calibration and are not included in this grid.
  5. How consistent are the relationships among the observations, including topology?
    This grid represents processed SWATHplus-M interferometric bathymetry data gridded at 5-m resolution. Quality control and data processing were conducted to remove spurious points and reduce sound speed artifacts (refraction) using Computer Aided Resource Information System (CARIS) Hydrographic Information Processing System (HIPS v. 6.1)

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
Public domain data from the U.S. Government are freely re-distributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset. These data are not to be used for navigation.
  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)
  2. What's the catalog number I need to order this data set? Bathymetric data collected in the Belfast Bay, Maine pockmark field using a SWATHplus-M interferometric sonar in 2006 and 2008, by the U.S. Geological Survey: includes the GeoTIFF image BelfastBay_SWATHplus_bathymetry_5m.tif, the browse graphic BelfastBay_SWATHplus_bathymetry_5m_browse.jpg, and Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata (CSDGM) metadata file BelfastBay_SWATHplus_bathymetry_5m_meta.xml).
  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?
    To utilize this data, the user must have software capable of reading a 32-bit GeoTIFF.

Who wrote the metadata?

Last modified: 10-Dec-2020
Metadata author:
Brian Andrews
U.S. Geological Survey, Northeast Region
384 Woods Hole Road
Woods Hole, MA

508-548-8700 ext. 2348 (voice)
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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