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

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How should this data set be cited?

   U.S. Geological Survey, 2009, BATHY_GRD.ASC - Bathymetric data collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2006-2007 (ESRI ASCII GRID): Open-File Report 2008-1195, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

   Online Links:

   • <http://pubs.usgs.gov/of/2008/1195/GIS_catalog/Bathy/bathy_grd.zip>

   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:

   • <http://pubs.usgs.gov/of/2008/1195/>

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, 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: 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 02543-1598
   

   (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?

   (source 1 of 1)

   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.

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 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.

   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
   

   Date: 2007 (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.

   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 produced in this process:

   • BATHY

   (process 5 of 5)

   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 02543-1598
   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

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:

   • <http://www.tidesandcurrents.noaa.gov/hydro.html>

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

   Online Links:

   • <http://www.omg.unb.ca/~jonnyb/processing/definitive_swathed/index.html>

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

   Online Links:

   • <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.

   Online Links:

   • <http://gmt.soest.hawaii.edu/>

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?

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?
   • Availability in digital form:

     Data format:	WinZip file containing an ESRI ASCII grid of swath bathymetric data collected offshore of the Chandeleur Islands, LA, and associated metadata. in format WinZip (version 9.0) Size: 5.000 Mbytes
     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: 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:

• <http://www.esri.com/metadata/esriprof80.html>
• <http://www.esri.com/metadata/esriprof80.html>