50-Meter Digital Elevation Model of Coastal Bathymetry Collected in 2012 from the Chandeleur Islands, Louisiana (U.S. Geological Survey Field Activity Numbers 12BIM03 and 12BIM04)

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Frequently anticipated questions:

What does this data set describe?

Title:
50-Meter Digital Elevation Model of Coastal Bathymetry Collected in 2012 from the Chandeleur Islands, Louisiana (U.S. Geological Survey Field Activity Numbers 12BIM03 and 12BIM04)
Abstract:
As part of the Barrier Island Evolution Research Project, scientists from the U.S. Geological Survey's St. Petersburg Coastal and Marine Science Center conducted nearshore geophysical surveys off the northern Chandeleur Islands, Louisiana, in Julyof 2012. The overall objective of the study is to better understand barrier-island geomorphic evolution, particularly storm-related depositional and erosional processes that shape the islands over annual to interannual timescales (1-5 years). The collection of geophysical data will allow us to identify relationships between the geologic history of the island and its present day morphology and sediment distribution. This mapping effort was the first in a series of three planned surveys in this area. High resolution geophysical data collected in each of 3 consecutive years along this rapidly changing barrier-island system will provide a unique time-series dataset that will significantly further the analyses and geomorphological interpretations of this and other coastal systems, improving our understanding of coastal response and evolution over short time scales (1-5 years). This report serves as an archive of processed interferometric swath and single-beam bathymetry data that were collected during two cruises (USGS Field Activity Numbers 12BIM03 and 12BIM04) along the northern portion of the Chandeleur Islands, Breton National Wildlife Refuge, Louisiana, in July of 2012. Geographic information system data products include a 50 m-cell-size interpolated bathymetry grid surface, trackline maps, and point data files. Additional files include error analysis maps, Field Activity Collection System logs, and formal Federal Geographic Data Committee metadata.
Supplemental_Information:
Both the single-beam and swath surveys were acquired and processed to a geodetic reference ellipsoid. The swath survey used OmniSTAR High Precision for the Differential Geographic Positioning System (DGPS) at datum ITRF2005, and the single-beam post-processed DGPS navigation was referenced to WGS84 (G1150)/ITRF00. Both datasets were transformed horizontally to NAD83 and then vertically to NAVD88 using GEOID09 (NOAA NGS VDatum software version 3.2 - http://vdatum.noaa.gov/) and the final x,y,z position data from each survey were merged to generate a digital elevation model with a resolution of 50-meter cell size.
  1. How might this data set be cited?
    U.S. Geological Survey, 2014, 50-Meter Digital Elevation Model of Coastal Bathymetry Collected in 2012 from the Chandeleur Islands, Louisiana (U.S. Geological Survey Field Activity Numbers 12BIM03 and 12BIM04):.

    Online Links:

    This is part of the following larger work.

    DeWitt, Nancy T., Bernier, Julie C., Pfeiffer, William R., Miselis, Jennifer L., Flocks, James G., Reynolds, B.J., Wiese, Dana S., and Kelso, Kyle W., 2014, Coastal Bathymetry Data Collected in 2012 from the Chandeleur Islands, Louisiana: U.S. Geological Survey Data Series 847, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.916815
    East_Bounding_Coordinate: -88.795726
    North_Bounding_Coordinate: 30.096010
    South_Bounding_Coordinate: 29.908091
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 12-Jul-2012
    Ending_Date: 04-Aug-2012
    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 413 x 227 x 1, type Grid Cell
    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: 0.9996
      Longitude_of_Central_Meridian: -87.0
      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 50
      Ordinates (y-coordinates) are specified to the nearest 50
      Planar coordinates are specified in meter
      The horizontal datum used is D North American 1983.
      The ellipsoid used is GRS 1980.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.
      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: North American Vertical Datum 88 (NAVD88)
      Depth_Resolution: 0.1
      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
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Nancy T. DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov

Why was the data set created?

This 50-meter cell size digital elevation model is an interpretive product that was derived from the processed single-beam and interferometric swath bathymetry data collected in July of 2012 around the northern 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: 2012 (process 1 of 9)
    GPS Acquisition: A GPS base station was erected at a temporarily installed USGS benchmark (TMRK) located on the sound side of the Chandeleur Islands. A second base station (BERM) was erected on the furthest northern island, providing differential GPS coverage for the survey area within a 15 kilometer (km) radius of either benchmark. GPS receivers recorded the 12-channel full-carrier- phase positioning signals (L1/L2) from satellites via the Thales choke-ring antenna at the base stations. This GPS instrument combination was duplicated on the single-beam survey vessel (rover). The base receiver and the rover receiver record their positions concurrently at 1-second (s) recording intervals throughout the survey. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy T. DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Date: 2012 (process 2 of 9)
    Single-Beam Bathymetry Acquisition: The single-beam bathymetric data were collected aboard the 22-foot RV TwinVee. Boat motion was recorded at 50-millisecond (ms) intervals with a Teledyne TSS Dynamic Motion Sensor (TSS DMS-05). HYPACK version 10.0.5.31, a marine surveying, positioning, and navigation software package, managed the planned-transect information and provided real-time navigation, steering, correction, data quality, and instrumentation-status information to the boat operator. Depth soundings were recorded at 50 ms intervals with a Knudsen 320BP echosounder system using a 200 kilohertz (kHz) transducer. Data from the GPS receiver, motion sensor, and fathometer were recorded in real-time and merged into a single raw data file (.raw) in HYPACK. Each device string was referenced by a device identification code and time stamped to UTC. Sound velocity measurements were collected using an Applied Microsystems Smart Sound Velocity Profiler (SVP). The instrument was cast overboard periodically, throughout the survey, to observe changes in water column speed of sound (SOS). Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy T. DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Date: 2012 (process 3 of 9)
    Swath Bathymetry Acquisition: The interferometric swath bathymetry data were collected aboard the RV Survey Cat using a SEA SWATHplus-H 468 kHz interferometric sonar system mounted on a sled attached to a rail system, which was fastened between the catamaran halls. This allowed the instrument to align directly below the GPS antennae and minimize geometry errors. Boat position and motion data were recorded in real-time with a CodaOctopus F190R wetpod inertial measurement unit(IMU) mounted underwater between the transducer heads, to minimize lever arm geometry errors between the observed depths and associated vessel motion. Real-time corrected positions were acquired with an OmniSTAR HP (High-Precision differential global navigation satellite system) satellite constellation subscription. OmniSTAR HP position correction data and motion data from the IMU were integrated with interferometric soundings in the SWATHplus software package versions 3.7.17, with positional and calibration offsets pre-defined by a session file(.sxs), allowing for real-time- corrected depths. Prior to deployment, all equipment offsets were surveyed in dry dock with a laser total station. During the survey, all swath tracklines were recorded in SEA SWATHplus raw data format (.sxr). A Valeport Mini Sound Velocity Sensor (SVS) was attached to the transducer mount and collected continuous speed of sound (SOS) measurements at the depth of the transducers. These values were directly read and incorporated into the SWATHplus acquisition software, giving real-time speed of sound at the transducer while underway. In addition, a separate sound velocity profiler (Valeport miniSVP) was used to collect SOS profiles (water surface to seafloor) at intervals throughout the survey. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy T. DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Date: 2013 (process 4 of 9)
    Swath Bathymetry Processing: Position data recorded by the Coda-Octopus F190R IMU system were corrected in real time via the OmniSTAR HP differential navigation system. The IMU applied real-time motion corrections for heave, roll, and pitch to the vertical component of each position fix. The corrected positions were integrated with the observed bathymetric values to calculate a final ellipsoid height and position, representing the elevation of the seafloor with respect to the geodetic reference frame ITRF05 across the swath range. SWATHplus served as both an acquisition software and initial processing software. Preliminary roll calibration trackline data were collected and processed with Systems Engineering and Assessment Ltd SWATHplus and Grid Processor software version 3.7.17. Instrument offset and calibration values were entered into the session file (.sxs) and the raw data files (.sxr) were processed using the updated system configuration containing roll calibration values, measured equipment offsets, acquisition parameters, navigation and motion from the F190R, SOS at the sonar head, and SVP cast data. Any calibration offsets or acoustic filtering applied in SWATHplus was also written to the processed data file (.sxp). The initial real-time processing datum for the swath and backscatter data was ITRF05, which is the acquisition datum for OmniSTAR HP position and navigation data. Processed data files were imported into CARIS HIPS and SIPS version 7.1, and original sounding data were edited for outliers using the program's depth filters and reference surfaces. Remaining outliers were deleted out manually. A CARIS Bathymetry with Associated Statistical Error (BASE) surface with associated Combined Uncertainty and Bathymetry Estimator(CUBE) sample surface was created from the edited soundings dataset. A BASE hypothesis is the estimated value of a grid node representing all soundings within a chosen resolution or grid-cell size (for example, 5 m) weighted by uncertainty and proximity, giving the final value as a "sample" of the data within the specific grid cell. This algorithm allows for multiple grid-node hypotheses to be verified or overridden by the user, while maximizing processing efficiency. A 5-m resolution CUBE surface was created to perform initial hypothesis editing using the CARIS Subset Editor tool, followed by higher resolution surface detail editing within the subset editor. The sample x,y,z data were exported as ASCII text at a 5-m by 5-m sample resolution in the ellipsoid datum of ITRF05. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Data sources produced in this process:
    • 12BIM03_IFB_04_005_ITRF05.txt
    Date: 2013 (process 5 of 9)
    Differentially Corrected Navigation Processing: The coordinate values of the GPS base station (TMRK) are the time-weighted average of values obtained from the National Geodetic Survey's On-Line Positioning User Service (OPUS). The base station coordinates were imported into GrafNav version 8.1 (Waypoint Product Group) and the kinematic GPS data from the survey vessel were post-processed to the concurrent GPS session data at the base stations. During processing, steps were taken to ensure that trajectories between the base and the rover were clean, resulting 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 that had cycle slips could be excluded, or the satellite elevation mask angle could be adjusted to improve the position solutions. The final differentially corrected precise DGPS positions were computed at 1-second (s) intervals for each rover GPS session and exported in ASCII text format to replace the uncorrected real-time rover positions recorded during acquisition. The GPS data were processed and exported in World Geodetic System of 1984 (WGS84) (G1150) geodetic datum. Data sources produced in this process:
    • Post-processed differential navigation data for the rover (boat) in ASCII text format. 3 files-forward, reverse, and combined trajectories- are produced for each GPS session file.
    Date: 01-Jun-2012 (process 6 of 9)
    Single-beam bathymetry processing: All data were processed with CARIS HIPS and SIPS (Hydrographic Information Processing System and Sonar Information Processing System) version 7.1. The raw HYPACK (version 10.0.5.31) data files were imported into CARIS; the differentially corrected navigation files were imported using the generic data parser tool within CARIS; and any SVP profile casts were entered and edited using the SVP editor within CARIS. The bathymetric data components-position, motion, depth, and SOS- were merged and geometrically corrected in CARIS to produce processed x,y,z data. Next the data were edited for outliers and further reviewed in the Subset Editor utility for crossing status, and questionable data points or areas. The geometrically corrected point data were then exported as an x,y,z ASCII text file referenced to WGS84(G1150), which is equivalent to ITRF00, and ellipsoid height in meters. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Data sources used in this process:
    • Post-processed differential navigation data and raw HYPACK bathymetric data in ASCII text format.
    Data sources produced in this process:
    • 12BIM04_SBB_ITRF00_03_xxx.txt
    Date: 2013 (process 7 of 9)
    Datum transformation: Using the transformation software VDatum version 3.2, both the interferometric swath and single-beam bathymetric data were transformed horizontally from their data acquisition datums-swath, ITRF05; single-beam, ITRF00- to the North American Datum of 1983 (NAD83) reference frame and the orthometric vertical datum NAVD88 using the National Geodetic Survey (NGS) geoid model of 2009 (GEOID09). Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Data sources used in this process:
    • 12BIM03_IFB_04_005_ITRF05.txt
    • 12BIM04_SBB_ITRF00_03_xxx.txt
    Data sources produced in this process:
    • 12BIM03_IFB_NAD83_NAVD88_GEOID09.txt
    • 12BIM04_SBB_NAD83_NAVD88_GEOID09.txt
    Date: 2013 (process 8 of 9)
    Gridding Bathymetric data: Using Esri ArcGIS version 10.1, the swath and the single-beam elevations were examined for spatial distribution and vertical agreement. After combining the point data (x,y,z), a triangulated irregular network (TIN) was generated. The TIN surface and elevation point- shapefile were used in conjunction to visually scan for any remaining discrepancies. Once all data were reviewed, a 50-m by 50-m cell resolution digital elevation model (DEM) was generated using the natural neighbor algorithm in ArcGIS software. A raster mask was created from the polygon survey extent with the ArcGIS "polygon to raster" conversion tool. The DEM was then clipped to the raster mask using the ArcGIS Spatial Analyst "extract by raster mask" tool. To help reduce uncertainty in the final DEM, the ArcGIS Spatial Analyst "neighborhood" low pass raster-data filter was applied. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nancy DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Data sources used in this process:
    • 12BIM03_IFB_NAD83_NAVD88_GEOID09.txt
    • 12BIM04_SBB_NAD83_NAVD88_GEOID09.txt
    Data sources produced in this process:
    • Chandeleurs_2012_50_NAD83_NAVD88_GEOID09_DEM.tif
    Date: 13-Oct-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?

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. The single-beam and interferometric swath bathymetry data were collected during concurrent research cruises in July, 2012. Methods are employed to maintain data collection consistency aboard various platforms. During mobilization, each piece of equipment, single-beam and swath, is isolated to obtain internal and external offset measurements with respect to the survey platform. All critical measurements are recorded manually and digitally and entered into their respective programs for calibration. Once calibration is complete and the calibration status is considered acceptable, survey operations commence. Each system has a dedicated computer, and efforts are made to use the same equipment and software versions on both systems. However, upgrades and changes can occur and require additional setup, measurements, and notation. For single-beam bathymetry, offsets between the single beam transducers and the Ashtech antenna reference point (ARP) were measured and accounted for in post-processing. Bar checks were performed as calibration efforts and accounted for any drift in the echosounder. Differential Geographic Positioning System (DGPS) coordinates were obtained using post-processing software packages (National Geodetic Survey On-Line Positioning User Service, OPUS, and Waypoint Product Group GrafNav, version 8.3). For the interferometric swath bathymetry, offsets between the sonar head and the DGPS antennas were measured and entered into the CodaOctopus F190R internal setup program. DGPS was provided through the OmniSTAR High Performance wide-area GPS service. DGPS is always implemented for navigational accuracy either during acquisition or as a post-processing step. These bathymetric data have not been independently verified for accuracy.
  2. How accurate are the geographic locations?
    All static base station sessions were processed through the On-Line Positioning User Service (OPUS) maintained by the National Oceanic and Atmospheric Administration (NOAA) and the National Geodetic Survey (NGS). The base location results from OPUS were entered into a spreadsheet to compute a final, time-weighted positional coordinate-latitude, longitude, and ellipsoid height-. Base station positional error for each GPS session was calculated as the absolute value of the final position minus the session position value. The maximum horizontal error of the base station coordinates used for post-processing the single-beam bathymetry was 0.00042 seconds latitude and 0.00096 seconds longitude for TMRK and 0.00036 seconds latitude and 0.00047 seconds longitude for BERM. The stated horizontal accuracy of the OmniSTAR HP navigation subscription used during swath bathymetry acquisition is reported by the service as +/-15 centimeters (cm)(95 percent of the time).
  3. How accurate are the heights or depths?
    All static base station sessions for TMRK and BERM were processed through the On-Line Positioning User Service (OPUS) maintained by the National Oceanic and Atmospheric Administration (NOAA) and the National Geodetic Survey (NGS). The base location results from OPUS were entered into a spreadsheet to compute a final, time-weighted positional coordinate-latitude, longitude, and ellipsoid height. Base station positional error for each GPS session was calculated as the absolute value of the final position minus the session position value. SPCMSC standards define the maximum acceptable vertical error for any individual base station GPS session as less than or equal to 3 times the standard deviation of the ellipsoid height; any occupations exceeding this error are removed and the base station coordinates are recalculated. For the TMRK base location the standard deviation of the ellipsoid height was 0.014 m, and the maximum difference from the average ellipsoid for any GPS session was +/- 0.030 m. For BERM base location the standard deviation of the ellipsoid height was 0.021 m and the maximum difference from the average ellipsoid for any GPS session was +/- 0.031 m. All the processed single-beam bathymetry data (x,y,z) for 2012 are referenced to these base station coordinates. The differentially corrected navigation files-base station GPS processed to boat GPS- were exported from GrafNav and then imported into CARIS HIPS and SIPS version 7.1, and then merged, by time, with the HYPACK (version 10.0.5.31) raw data files, at which point the soundings were geometrically corrected for motion and speed of sound. For the single-beam soundings, elevation differences at all trackline crossings were less than or equal to 0.14 m, and the elevation differences were within +/- 0.10 m for 89.28 percent of the 653 crossings. The stated vertical accuracy of the OmniSTAR HP navigation subscription used during swath bathymetry acquisition is +/-0.15 m (95 percent of the time). The Coda Octopus F190R IMU, which integrates the OmniSTAR HP position with motion, measures vessel velocity (+/- 0.014 meters/second (m/s)), roll and pitch (< 0.025 degrees), heading (1 m baseline 0.1 degrees), and heave (5 cm per meter (m) of depth). The vertical accuracy for the SWATHplus-H system varies with depth and across track range. At 57 m it is accurate to 10 cm vertically. Maximum vertical transformation error reported by VDatum is 0.171 m or 17.1 cm for eastern Louisiana. The sum of the errors (+/- 0.031 m plus +/-0.15 m plus 0.171 m) in the vertical is equal to +/-.352 m or +/- 35.2 cm.
  4. Where are the gaps in the data? What is missing?
    This is a completely processed digital elevation model representing an interpolated bathymetric surface derived from the acoustic interferometric swath and single-beam bathymetry data.
  5. How consistent are the relationships among the observations, including topology?
    The single-beam and interferometric swath bathymetry data were collected during concurrent research cruises in July, 2012. Refer to the online data series linkage for field logs, vessel platform descriptions, and other survey information. This dataset was created to provide a single post-processed bathymetric grid from the merged datasets. The digital elevation model is 50-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
Use_Constraints:
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)
    U.S. Geological Survey
    Attn: Nancy DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@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?
    This publication was prepared by an agency of the United States Government. Although these data were 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 a GeoTIFF file. To utilize this data, the user must have a GIS software package capable of reading .tif format.

Who wrote the metadata?

Dates:
Last modified: 13-Oct-2020
Metadata author:
U.S. Geological Survey
Attn: Nancy DeWitt
Geologist
600 4th Street South
St. Petersburg, FL
USA

727-502-8000 (voice)
ndewitt@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/Chan12_DEM_metadata.faq.html>
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