Digital Elevation Model from Single Beam Bathymetry XYZ Data Collected in June 2015 from the Chandeleur Islands, Louisiana

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Frequently anticipated questions:

What does this data set describe?

Digital Elevation Model from Single Beam Bathymetry XYZ Data Collected in June 2015 from the Chandeleur Islands, Louisiana
As part of the Louisiana Coastal Protection and Restoration Authority (CPRA) Barrier Island Comprehensive Monitoring Program (BICM), scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center conducted a single-beam bathymetry survey around the Chandeleur Islands, Louisiana in June 2015. The goal of the program is to provide long-term data on Louisiana’s barrier islands and use this data to plan, design, evaluate, and maintain current and future barrier island restoration projects. The data described in this report, along with USGS bathymetry data collected in 2013 as a part of the Barrier Island Evolution Research project covering the northern Chandeleur Islands, and data collected in 2014 in collaboration with the Louisiana CPRA Barrier Island Comprehensive Monitoring project around Breton Island, will be used to assess bathymetric change since 2006-2007 and serve as a bathymetric control in supporting modeling of future changes in response to restoration and storm impacts. The survey area encompasses approximately 435 square kilometers (km2) of nearshore and back-barrier environments around Hewes Point, the Chandeleur Islands, and Curlew and Grand Gosier Shoals. This data series serves as an archive of processed single-beam bathymetry data, collected in the nearshore of the Chandeleur Islands, Louisiana from June 17-24, 2015 during USGS Field Activity Number 2015-317-FA. Geographic information system data products include: a 200 meter-cell-size interpolated bathymetry grid, trackline maps, and xyz point data files. Additional files include error analysis maps, Field Activity Collection System logs, and formal Federal Geographic Data Committee metadata.
The final DEM, CHAND_2015_DEM, was created from single-beam bathymetry data collected during 2015-317-FA, which encompasses data from three separate survey platforms; the R/V Sallenger (15BIM01), R/V Jabba Jaw (15BIM02) and R/V Chum (15BIM03). The single-beam bathymetry corrected positions were obtained through post processing of the base station data to the concurrent rover data. All datasets were transformed from their initial datum International Terrestrial Reference Frame of 2000 (ITRF00) to the North American Datum of 1983 (NAD83), using GEOID12A (NOAA NGS VDatum software 3.2 - The Final x,y,z position data were gridded at a 200-meter cell size resolution to create the digital elevation model which represents elevations from -0.20 to -15.40 meters.
  1. How might this data set be cited?
    U.S. Geological Survey, 2016, Digital Elevation Model from Single Beam Bathymetry XYZ Data Collected in June 2015 from the Chandeleur Islands, Louisiana:.

    Online Links:

    This is part of the following larger work.

    Stalk, Chelsea A., DeWitt, Nancy T., Bernier, Julie C., Kindinger, Jack L., Flocks, James G., Miselis, Jennifer L., Locker, Stanley D., Kelso, Kyle W., and Tuten, Thomas M., 2016, Coastal Single-Beam Bathymetry Data Collected in 2015 from the Chandeleur Islands, Louisiana: U.S. Geological Survey Data Series 1039, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -89.082427
    East_Bounding_Coordinate: -88.759255
    North_Bounding_Coordinate: 30.117966
    South_Bounding_Coordinate: 29.552396
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 17-Jun-2015
    Ending_Date: 24-Jun-2015
    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 311 x 151 x 1, type Grid Cell
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 16
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -87
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 200
      Ordinates (y-coordinates) are specified to the nearest 200
      Planar coordinates are specified in meter
      The horizontal datum used is NAD83 North American Datum 1983.
      The ellipsoid used is Geiod 12A.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.
      Depth_Datum_Name: NAVD88 North American Vertical Datum 1988
      Depth_Resolution: 0.10
      Depth_Distance_Units: meter
      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)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
    U.S. Geological Survey, Coastal and Marine Geology Program, St. Petersburg Coastal and Marine Science Center (SPCMSC).
  3. To whom should users address questions about the data?
    Cherokee Nation Technologies/U.S. Geological Survey
    Attn: Chelsea A. Stalk
    Researcher I
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)

Why was the data set created?

This 200-meter cell size digital elevation model (DEM) is an interpretive product that was derived from the processed single-beam bathymetry data collected in June 2015 from the nearshore environments of the Chandeleur Islands, Louisiana.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 2015 (process 1 of 5)
    DGPS Navigation Processing: Geographic Positioning Systems (GPS) base stations were re-occupied by USGS personnel for the purpose of this survey. The names of the benchmarks used were: MRK3, located to the north of the survey area on a bank near the Pelican fishing camp, SM01 located in the middle of the survey area on the landward shore of Monkey Bayou, and GRIG located in the southern portion of the survey area atop a retired oil drilling platform ( overview.html). All base stations were occupied 24 hours and equipped with Ashtech Proflex GPS receivers recording 12-channel full-carrier-phase positioning signals (L1/L2) from satellites via Thales Choke-ring antennas, recording at a rate of 0.1 seconds (s). GPS apparatus was duplicated on all survey platforms with the exception of the Personal Water Craft (PWC) (15BIM03) in which a smaller, Ashtech Global Navigation Satellite Systems (GNSS) antenna was used. The base receivers and rover receivers recorded positions concurrently. R/V Chum recorded at 0.1 s throughout the survey while the R/V Jabba Jaw and the R/V Sallenger (JD 172-175) recoded at 0.2 s, R/V Sallenger recorded at 1.0 second the first 4 days of the survey (JD168-171). The coordinate values for each of the GPS base stations (MRK3, SM01, GRIG) are the time-weighted average of values obtained from the National Geodetic Survey's (NGS) On-Line Positioning User Service (OPUS). All base station sessions of recorded data are decimated to 30 seconds for efficient processing, and then submitted to OPUS via the online service. All solutions are then returned to the user and entered into a spreadsheet where time-weighted ellipsoid values are calculated for each station for the entire occupation. Any individual ellipsoid value that falls outside three standard deviations for the entire occupation was excluded and the final coordinate values were then determined. The final base station coordinates were imported into GrafNav version 8.5 (Waypoint Product Group) and the kinematic GPS data from the survey vessel were post-processed to the concurrent GPS data from the base stations. In all cases the closest base station to the roving vessel was utilized to help keep vertical error to a minimum. During processing, steps were taken to ensure that the trajectories between the base and rover were clean and resulted in fixed positions. By analyzing the graphs, trajectory maps, and processing logs that GrafNav produces for each GPS session, GPS data from satellites flagged by the program as having poor health or satellite time segments with cycle slips were excluded, and the satellite elevation mask angle was adjusted to improve the position solutions when necessary. The final, differentially-corrected, precise DGPS positions were computed at their respective time intervals, and then exported in ASCII text format. The file was then used to replace the uncorrected real-time rover positions recorded during acquisition. The GPS data were processed and exported in the World Geodetic System of 1984 (WGS84) (G1150) geodetic datum UTM zone 16N. Person who carried out this activity:
    Cherokee Nation Technologies/U.S. Geological Survey
    Attn: Chlesea A. Stalk
    Researcher I
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    Date: 2015 (process 2 of 5)
    Single Bream Processing: The raw HYPACK® data files were imported into CARIS HIPS and SIPS® (Hydrographic Information Processing System and Sonar Information Processing System) version 9.0.17. The corrected DGPS positions exported from GrafNav were imported into CARIS using the generic data parser tool. After parsing, the navigation data were scanned using the Navigation Editor, which allows the user to view multiple types of plots including trackline orientation, timing, and course direction. This check verifies if the parsed data corresponds to the processed DGPS. Next, Speed of Sound (SOS) Profile (SVP) casts were entered, and edited, using the SVP editor tool, and then applied as nearest in distance within time. All soundings are referenced to the ellipsoid (WGS84, ITRF00) during processing, this involved a step in CARIS to compute the GPS tide. The GPS tide represents the ellipsoidal surface. GPS tide and GPS height are then compared against each other to ensure correct computation by the program and applied GPS antenna height provided in the vessel file. All bathymetric data components; position, motion, depth, GPS tide, and Speed of Sound (SOS), were then merged and geometrically corrected in CARIS to produce processed x,y,z data. Once merged the dataset is reviewed for erroneous points using the Single Beam Editor. The points that are visually obvious outliers are often related to cavitation in the water column obscuring the fathometer signal, tight turns in the surf zone affecting the tracking of the incoming GPS signal, and/or false readings due to general equipment issues. Data showing these are either discarded or adjusted to surrounding sounding depths. Also, data points in areas of extremely shallow water (0.30 m to 0.50 m) such as shoals and seagrass beds are reviewed against the surrounding data for overall consistency. Finally, a Bathymetry with Associated Statistical Error (BASE) surface is created. Using the Subset Editor, the BASE surface is used as a color coded guide to pinpoint crossings that are visually offset from one another. If an offset is identified, it is further examined and is reprocessed if necessary. The geometrically-corrected point data are then exported as an x,y,z ASCII text file referenced to WGS84 (G1150), equivalent to ITRF00, UTM 16, and ellipsoid height in meters. The single-beam bathymetry datasets combined (15BIM01, 15BIM02, and 15BIM03) consists of 8,224,799 point elevations with an ellipsoidal elevation range of -43.927 to -25.966 m. Person who carried out this activity:
    Cherokee Nation Technologies/U.S. Geological Survey
    Attn: Cheslea A. Stalk
    Researcher I
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    Data sources produced in this process:
    • 15BIM01_SBB_Level_02_1039_ITRF00.txt 15BIM02_SBB_Level_02_1039_ITRF00.txt 15BIM03_SBB_Level_02_1039_ITRF00.txt
    Date: 2015 (process 3 of 5)
    Quality Control and Quality Assurance (QA/QC) and Datum transformation: All Single-beam data found in the ASCII exported from CARIS were imported into Esri ArcMap version 10.2, where a shapefile of the individual data points (x,y,z) was created and plotted in 1-m color coded intervals. First, all data were visually scanned for any obvious outliers or problems. A Python script was used for the purpose of evaluating elevation differences at the intersection of crossing tracklines by calculating the elevation difference between points at each intersection using an inverse distance weighting equation. GPS cycle slips, stormy weather conditions, and rough sea surface states can contribute to poor data quality. If discrepancies that exceed the acceptable error threshold were found, then the line in error was either removed or statically adjusted by the average of the crossings within the line. The script was run on all vessel point data first on a vessel by vessel basis and then run a final time for all data points from all vessels collectively. For this dataset, the collective run, using a merged shapefile of all vessel point data, is the most important as the survey structure did not allow for sufficient vessel crossing, rather vessels crossing other vessels. Once the dataset passed all QA/QC procedures and manual editing steps, the data were considered final. The final x,y,z (WGS84, ITRF00) Ellipsoid point data was exported into a ASCII text file by use of the ArcGIS extension "XTools Pro" Export table to file function and made available for download via the survey product page of the accompanying Data Series. Person who carried out this activity:
    Cherokee Nation Technologies/U.S. Geological Survey
    Attn: Chelsea A. Stalk
    Researcher I
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    Data sources produced in this process:
    • 15BIM01_SBB_Level_03_1039_ITRF00.txt 15BIM02_SBB_Level_03_1039_ITRF00.txt 15BIM03_SBB_Level_03_1039_ITRF00.txt
    Date: 2015 (process 4 of 5)
    Transformation, Gridding and RMS Calculation: The final sounding data that contribute to the Digital Elevation Model (DEM) were transformed horizontally and vertically into North American Datum 1983 (NAD83) (CORS96), UTM Zone 16N and North American Vertical Datum 1988 (NAVD88) orthometric height using the GEOID12A geoid model using the National Oceanic and Atmospheric Association (NOAA) VDatum version 3.2 transformation software (reported vertical transformation error is 5.4 cm). The resulting orthometric heights (elevations) for all survey vessels ranged from 0.01 m to -15.40 m. The NAVD 88 point elevations were imported into ESRI’s ArcMap version 10.2, merged using the data management "merge" tool to create shape file (2015_317_FA_SBB_Level_03_1039_NAD83_NAVD88_GD12A.shp) and gridded using the 3D Analyst and Spatial Analyst toolsets. A triangulated irregular network (TIN) was created from the shapefile containing the final point data using the "create tin" tool, and the data were then converted into a digital elevation model (DEM) using the "tin to raster” tool and natural neighbors algorithm with a cell size of 200 m. A bounding polygon representing the extent of survey tracklines was created and converted into a raster mask using the ArcGIS "polygon to raster" tool, and the interpolated DEM was clipped to this survey extent using the "extract by mask" tool. The final product is a DEM of the entire survey extent; grid values range from -0.00 m maximum to -15.40 m minimum. In order to evaluate how well the DEM represents the final sounding data both spatially and quantitatively, a comparison of the DEM cell value versus the final point elevations were plotted in ArcGIS using the “extract values by points” spatial analyst tool. This tool extracts the value represented by the underlying grid and compares it to that of the overlying point data. The root mean square (RMS) error, quantified as the difference between the measured depth and the grid depth values, was calculated for the entire survey using the generic RMS equation. Observed point elevations were subtracted from the values extracted from the grid, and the squared sum was divided by the number of samples represented by the grid. The RMS for the entire survey equals 0.23. Person who carried out this activity:
    Cherokee Nation Technologies/U.S. Geological Survey
    Attn: Chelsea A. Stalk
    Researcher I
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    Data sources used in this process:
    • 2015_317_FA_SBB_NAD83_UTM16N_NAVD88_GEOID12A.txt
    Data sources produced in this process:
    • CHAND_2015_DEM.tif
    Date: 13-Oct-2020 (process 5 of 5)
    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)
  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?
    The accuracy of the data is determined during data collection. Methods are employed to maintain data collection consistency aboard various platforms. During mobilization, each piece of equipment is isolated to obtain internal and external offset measurements with respect to the survey platform. All the critical measurements are recorded manually and digitally and entered into their respective programs for calibration, acquisition, and post processing. Each system has a dedicated computer, and efforts are made to utilize the same equipment and software versions on all systems. However, upgrades and changes occur and require additional setup, measurements, and notation. DGPS is always implemented for navigational accuracy as a post-processing step. These bathymetric data have not been independently verified for accuracy, rather verified as a whole product.
  2. How accurate are the geographic locations?
    The stated horizontal accuracy of the Ashtech Proflex 500 and 800 GPS receivers used during single-beam bathymetry acquisition is reported by the service as +/-10 mm for Kinematic surveying.
  3. How accurate are the heights or depths?
    The stated vertical accuracy of the Ashtech Proflex 500 and 800 GPS units used during single-beam bathymetry acquisition is +/- 10 mm. The Teledyne TSS-DMS-05 MRU which integrates the DGPS position with motion proposes accuracy of roll and pitch (+/- 0.05 degrees), and heave (5% of heave amplitude or 5 cm). The vertical accuracy for the Odom Echtrac CV100 unit used on all survey platforms is 0.01 m +/- 0.1% of the depth value.
  4. Where are the gaps in the data? What is missing?
    This is a completely processed bathymetric DEM representing an interpolated bathymetric surface derived from final single-beam bathymetry data.
  5. How consistent are the relationships among the observations, including topology?
    The single beam bathymetry data were collected during one research cruise in June 2015 (2015-317-FA). Refer to the online Data Series linkage for field logs, vessel platform descriptions, and other survey information. This dataset was created to provide a post-processed bathymetric grid from the data and accompanying x,y,z deliverables. The DEM is 200-meter cell-size resolution; data gaps between acquisition tracklines are predicted values generated by the gridding algorithm.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
The U.S. Geological Survey requests that it be referenced as the originator of this dataset in any future products or research derived from these data. These data should not be used for navigational purposes.
  1. Who distributes the data set? (Distributor 1 of 1)
    Cherokee Nation Technologies/U.S. Geological Survey
    Attn: Chelsea A. Stalk
    Researcher 1
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
  2. What's the catalog number I need to order this data set? Chand_2015_DEM.tif
  3. What legal disclaimers am I supposed to read?
    This publication was prepared by an agency of the United States Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.
  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 raster contained in the .zip file is available as GeoTIFF.

Who wrote the metadata?

Last modified: 13-Oct-2020
Metadata author:
Cherokee Nation Technologies/U.S. Geological Survey
Attn: Chelsea A Stalk
Researcher I
600 4th Street South
St. Petersburg, FL

727-502-8000 (voice)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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