cont_1m - 1-meter contours produced from bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (polyline)

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Frequently-anticipated questions:

What does this data set describe?

Title:
cont_1m - 1-meter contours produced from bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (polyline)
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 should this data set be cited?

    U.S. Geological Survey, 2009, cont_1m - 1-meter contours produced from bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (polyline): Open-File Report 2008-1195, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole 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, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -89.281618
    East_Bounding_Coordinate: -88.763390
    North_Bounding_Coordinate: 30.109513
    South_Bounding_Coordinate: 29.384452

  3. What does it look like?

    <http://pubs.usgs.gov/of/2008/1195/images/cont_1m.jpg> (JPEG)
    color coded bathymetry contours

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

    Beginning_Date: 08-Jul-2006, 20070610
    Ending_Date: 19-Jul-2006, 20070622
    Currentness_Reference: ground condition

  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 raster data types:

      • Dimensions 1611 x 1029 x 1, type Grid Cell

    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 0.000000. Longitudes are given to the nearest 0.000000. 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:
      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?

    cont_1m
    depth contours (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.

    CONTOUR
    U.S. Geological Survey (Source: water depth)

    Range of values
    Minimum:-3
    Maximum:-15
    Units:meters below MLLW
    Resolution:0.1 meters

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 shapefile represents 1-meter interval bathymetric contours of 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?

    U.S. Geological Survey (source 1 of 2)
    U.S. Geological Survey.

    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.

    (source 2 of 2)
    Source_Contribution:
    This hillshaded grid (BATHY_HILLSH) was created from the bathymetric grid (BATHY) in this publications

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

    Date: 2006 (process 1 of 5)
    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 naviation 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.

    Person who carried out this activity:

    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov

    Date: 2006 (process 2 of 5)
    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)).

    Person who carried out this activity:

    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov

    Date: 2007 (process 3 of 5)
    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 02543-1598

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

    Data sources used in this process:
    • BATHY

    Data sources produced in this process:

    • cont_1m.shp

    (process 4 of 5)
    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. This grid was then reprojected with ArcToolbox (Data Management Tools - Projections and Transformations - Raster - Project Raster) to create a grid in geographic coordinate system WGS84.

    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

    Data sources used in this process:
    • BATHY

    Data sources produced in this process:

    • BATHY_DD

    (process 5 of 5)
    A shapefile containing 1-meter interval contours was then created using Xtools Pro for ArcGIS (version: 9.0; build 1420): Surface Tools - Convert grid to Contours.

    Person who carried out this activity:

    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

    Data sources used in this process:
    • BATHY_DD

    Data sources produced in this process:

    • cont_1m.shp

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

    Martin, Craig, unpublished material (2006, 2007), NOAA/NOS Hydrographic Planning Team (HPT) tide zone model.

    Online Links:

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

    Online Links:

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

    Online Links:

    P. Wessel and W. H. F. Smith, 1998, New, improved version of the Generic Mapping Tools released: EOS Transactions 79, American Geophyscial Union.

    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.

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

    Any spurious data 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:
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 02543-1598

    (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?

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

    This zip file contains data available in Environmental Systems Research Institute (ESRI) polyline shapefile format. The user must have ArcGIS or ArcView 3.0 or greater software to read and process the data file. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing the data. A free data viewer, ArcExplorer, capable of displaying the data is available from ESRI at www.esri.com.

Who wrote the metadata?

Dates:
Last modified: 27-Jan-2009
Metadata author:
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

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

Generated by mp version 2.8.14 on Thu Jan 29 11:09:57 2009