Bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (BATHY_GRD.ASC, ESRI ASCII GRID)

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Frequently anticipated questions:


What does this data set describe?

Title:
Bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (BATHY_GRD.ASC, ESRI ASCII GRID)
Abstract:
In 2006 and 2007, the U.S. Geological Survey, in partnership with Louisiana Department of Natural Resources and the University of New Orleans, conducted geologic mapping to characterize the sea floor and shallow subsurface stratigraphy offshore of the Chandeleur Islands in Eastern Louisiana. The mapping was carried out during two cruises on the R/V Acadiana. Data were acquired with the following equipment: an SEA Ltd SwathPlus interferometric sonar (234 kHz), Klein 3000 dual frequency sidescan sonar, and an Edgetech 512i chirp subbottom profiling system. The long-term goal of this mapping effort is to produce high-quality geologic maps and geophysical interpretations that can be utilized to investigate the impact of Hurricane Katrina in 2005 and to identify sand resources within the region.
  1. How might this data set be cited?
    U.S. Geological Survey, 2009, Bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (BATHY_GRD.ASC, ESRI ASCII GRID): Open-File Report 2008-1195, 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.

    Baldwin, Wayne E., Pendleton, Elizabeth A., and Twichell, David C., 2009, Geophysical Data from offshore of the Chandeleur Islands, Eastern Mississippi Delta: Open-File Report 2008-1195, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -89.298264
    East_Bounding_Coordinate: -88.751860
    North_Bounding_Coordinate: 30.117223
    South_Bounding_Coordinate: 29.382588
  3. What does it look like?
    http://pubs.usgs.gov/of/2008/1195/images/bathy_grd.jpg (JPEG)
    color coded image of bathymetry
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 08-Jul-2006
    Ending_Date: 22-Jun-2007
    Currentness_Reference:
    ground condition of two separate cruises - 20060708 to 20060719 and 20070610 to 20070622
  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 1727 x 1095 x 1, type Pixel
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 16
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -87.000000
      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 50.000000
      Ordinates (y-coordinates) are specified to the nearest 50.000000
      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.
      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: Mean lower low water
      Depth_Resolution: 0.5
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates
  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)
    • U.S. Geological Survey
  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

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

Why was the data set created?

This grid represents approximately 470 square km of bathymetric data that were collected in 2006 and 2007. These data are used to define the sea-floor morphology offshore of the Chandeleur Islands in Eastern Louisiana.

How was the data set created?

  1. From what previous works were the data drawn?
    raw bathy data (source 1 of 1)
    U.S. Geological Survey, Unpublished material, Bathymetry data collection.

    Type_of_Source_Media: disc
    Source_Contribution:
    Data acquisition at sea (2006; 2007): These bathymetric data were collected with a SEA Ltd Swathplus interferometric sonar (234 kHz) mounted on the portside of the R/V Acadiana of Loreauville, LA. The data were acquired during 2 cruises with SwathPlus Software (version: none) in July 2006 and June of 2007. Data were collected along tracklines spaced 100 to 125 m apart in the shore parallel direction and about 1 km apart in the shore perpendicular direction at a speed of 1.5 to 2.5 m/s. Sound velocity profiles were acquired approximately every 6 to 8 hours during the surveys using an Applied MicroSystems SVPlus Sound Velocimeter.
  2. How were the data generated, processed, and modified?
    Date: 2007 (process 1 of 9)
    A suite of processing software called SwathEd (version: none) developed by the University of New Brunswick - Ocean Mapping Group (<www.omg.unb.ca/~jhc/SwathEd.html>) was used to process, edit, and archive the bathymetric soundings after collection (Beaudoin, 2002). The processing and editing steps were: 1. The raw Submetrix 2000 Series data were 'unraveled'. This process creates several files on disk: bathymetric soundings, raw sidescan-sonar backscatter, navigation, parameter files describing the configuration of the system (i.e. offsets between motion reference unit and GPS antenna, etc), and sound velocity at the transducer and sound velocity profiler information. 2. The navigation data were edited on screen using the SwathEd routine 'jview' to remove undesirable points, including turns at the ends of survey lines. Jview also rejects stray GPS fixes outside of the survey area - a parameter set by the operator. 3. The soundings for each trackline were edited using SwathEd. Blocks of data across and along a trackline can be displayed in a SwathEd window. Anomalous points were identified by comparison to other points (i.e. standard deviation of a swath section) and removed in a process known as 'fluffing'. 4. The bathymetric soundings from each processed data file were mapped onto a Mercator grid (UTM zone 16N) from the original acquired projection which was geographic WGS84 using weigh_grid with grid nodes spaced at 5 meters. The weigh_grid program creates a Digital Terrain Model (DTM) by summing up the weighted contributions of all the provided data into the DTM. The weighted contributions only extend to a user defined region around the true location of the estimated depth value. Processing took place in 2006 and 2007. Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 2007 (process 2 of 9)
    The data were corrected for errors in soundings due to sound refraction, caused by variations in sound velocity profile, using the SwathEd refraction tool (version: none). 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, which is usually due to too widely spaced or non-existent velocity profiles within an area, results in an under or over-estimate of water depth which increases with distance from the center of the swath. For a discussion of how this effect can be recognized in a swath bathymetric data file, see <http://www.omg.unb.ca/AAAS/UNB_Seafloor_Mapping.html>. 2. The bathymetric data were corrected to mean lower low water using discrete tidal-zoning models (DTZ) developed by NOAA/NOS's Hdrographic Planning Team (Martin, personal communication, 2006; 2007) (<http://www.tidesandcurrents.noaa.gov/hydro.html.). The DTZ models corrected differences in tidal phase and amplitude between the survey areas and observations made at NOS tide gauges at Gulfport Harbor (8745557) in 2006, and Bay Waveland Yacht Club (8747437) in 2007. The tidal zone models were imported into CARIS (version: HIPS and SIPS 6.1) as text files and used to correct tidal observations for each survey. The corrected values were then exported from CARIS as ASCII text files and converted to binary files (using SwathEd 'binTide') that could be imported into SwathEd. 'mergeTide' in SwathEd was used to apply the corrected tidal data to the swath soundings creating new sounding values relative to MLLW. 3. A 5-meter grid of tide corrected bathymetric soundings was created using weigh_grid. 4. The processed 5-m bathymetric grid was converted from OMG .r4 format to ASCII x,y,z data in DMagic (Data Magician (version 6.4.0a, Build 474 Professional)). Processing took place in 2006 and 2007. Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 2007 (process 3 of 9)
    The 5-m ASCII x,y,z file (for each cruise; 2006 and 2007) was gridded in GMT (version: 4.2.1; Wessel and Smith, 1998) using 'blockmedian' with a cell size of 50 meters. This routine was conducted to minimize edge effects in the 'surface' gridding routine because these data were collected at approximately 45-50% seafloor coverage. Next a tension spline routine in GMT was used ('surface'). The tension was set to 0.25. Person who carried out this activity:
    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700 x2259 (voice)
    (508) 457-2310 (FAX)
    ependleton@usgs.gov
    Date: 2007 (process 4 of 9)
    The GMT grid (*.grd) was then converted to an ESRI Binary Grid via Mirone (version 1.2.3; Luis, 2007) and Matlab R2007b (version 7.5.0.342) - save grid as - ArcGIS binary grid. The projection was defined in ArcMap (version: 9.2; build 1420) using Data Management Tools - Projections and Transformations - Define Projection: UTM, zone 16N, WGS84 Datum. Person who carried out this activity:
    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2259 (voice)
    (508) 457-2310 (FAX)
    ependleton@usgs.gov
    Data sources produced in this process:
    • BATHY
    Date: Unknown (process 5 of 9)
    The ESRI Binary Grid was converted to an ASCII grid with an ESRI header using ArcToolbox (version 9.2; build 1420) -- Conversion Tools -- From Raster -- Raster to ASCII; in order to distribute these data via zipped files. Person who carried out this activity:
    Elizabeth A. Pendleton
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    (508) 548-8700 x2259 (voice)
    (508) 457-2310 (FAX)
    ependleton@usgs.gov
    Data sources used in this process:
    • BATHY_GRD
    Data sources produced in this process:
    • BATHY_GRD.ASC
    Date: 01-Nov-2016 (process 6 of 9)
    Edits to the metadata were made to fix any errors that MP v 2.9.34 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). The format of the time period of content had to be fixed. Formatting of the cross-references was fixed to meet the metadata standard. The source information was incomplete and had to be modified to meet the standard. The distribution format name was modified in an attempt to be more consistent with other metadata files of the same data format. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent. 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
    Date: 14-Feb-2017 (process 7 of 9)
    Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
    aallwardt@usgs.gov
    Date: 18-Nov-2019 (process 8 of 9)
    Crossref DOI link was added as the first link in the metadata. 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
    Date: 08-Sep-2020 (process 9 of 9)
    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?
    Martin, Craig, unpublished material, NOAA/NOS Hydrographic Planning Team (HPT) tide zone model.

    Online Links:

    Beaudoin, Jonathan, 2002, Hitchhiker's Guide to SwathEd...: Ocean Mapping Group - University of New Brunswick, Fredericton, New Brunswick, CA.

    Online Links:

    Luis, J. F., 2007, Mirone: A multi-purpose tool for exploring grid data.: Computers & Geosciences 33.

    Other_Citation_Details:
    Original online link that no longer seems valid: http://w3.ualg.pt/~jluis/mirone/mirone_Refs.htm
    P. Wessel and W. H. F. Smith, 1998, New, improved version of the Generic Mapping Tools released: EOS Transactions 79, American Geophyscial Union, Washington, D.C..

    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 navigated with a Differential Global Positioning System (DGPS), which is assumed to be accurate to +/- 1 to 2 meters, horizontally. Unless noted, all DGPS data are referenced to WGS84, and distance between sidemounted interferometric sonar and GPS antennae 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 0.1 m within the study area. In 2006, ship motion was recorded with a TSS DMS 2-05 and used to correct for vessel roll, pitch, heave, and yaw. In 2007, the Octopus F180 Attitude and Positioning system was used to correct ship motion. Tidal offsets were corrected with a NOAA tide zone model and referenced to mean lower low water. Errors associated with the tidal zone model could be less than or equal to the tidal range for this area which is ~0.4 m. The gridding algorithm and cell size used on these data could introduce errors as great as 3 m along the edges of the MRGO channel. Gridding-induced errors are likely much smaller (< 0.5 m) for most of the study area where slopes are less that 10 degrees. Changes in ship draft due to water and fuel usage were not considered.
  4. Where are the gaps in the data? What is missing?
    All shore parallel survey lines were incorporated. Tie (shore perpendicular) lines were not used in grid generation.
  5. How consistent are the relationships among the observations, including topology?
    Information unavailable from original metadata.

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:
These data are 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 as the originator of the dataset.
  1. Who distributes the data set? (Distributor 1 of 1)
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@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?
    • Availability in digital form:
      Data format: WinZip (version 9.0) file containing an ESRI ASCII grid of swath bathymetric data collected offshore of the Chandeleur Islands, LA, and associated metadata. in format AAIGrid (version ArcGIS 9.2) Size: 5.000
      Network links: http://pubs.usgs.gov/of/2008/1195/GIS_catalog/Bathy/bathy_grd.zip
      Media you can order: DVD-ROM (Density 4.75 Gbytes) (format UDF)
    • Cost to order the data: none

  5. What hardware or software do I need in order to use the data set?
    The grid contained in the GIS_catalog.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. The grid contained in the bathy_grd.zip file is available as an ASCII grid with an ESRI header. To utilize this data, the user must have a GIS software package capable of reading ASCII grids with ESRI headers, or be able to manipulate an ASCII matrix with a geospatial header. The ASCII raster files can be easily converted to ESRI grid format in either ArcView with Spatial Analyst extension (Import Data Source: ASCII Raster) or ArcGIS with Spatial Analyst extension (ASCII to Raster). The user should select floating point grid (as opposed to integer grid) when converting the bathymetry data.

Who wrote the metadata?

Dates:
Last modified: 08-Sep-2020
Metadata author:
Elizabeth A. Pendleton
U.S. Geological Survey
Geologist
384 Woods Hole Rd.
Woods Hole, MA

(508) 548-8700x2259 (voice)
(508) 457-2310 (FAX)
ependleton@usgs.gov
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/open_file_report/ofr2008-1195/bathy_grd_asc.asc.faq.html>
Generated by mp version 2.9.50 on Tue Sep 21 18:20:23 2021