50-Meter Digital Elevation Model of Coastal Bathymetry Collected in 2011 from the Chandeleur Islands, Louisiana (U.S. Geological Survey Field Activity Numbers 11BIM01 and 11BIM02)

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What does this data set describe?

Title:
50-Meter Digital Elevation Model of Coastal Bathymetry Collected in 2011 from the Chandeleur Islands, Louisiana (U.S. Geological Survey Field Activity Numbers 11BIM01 and 11BIM02)
Abstract:
As part of the Barrier Island Evolution Research Project, scientists from the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center conducted nearshore geophysical surveys off the northern Chandeleur Islands, Louisiana, in June of 2011. The overall objectives of the study are 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). 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 three 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 11BIM01 and 11BIM02) along the northern portion of the Chandeleur Islands, Breton National Wildlife Refuge, Louisiana, in June of 2011. 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:
The swath bathymetry data were collected and processed in the ITRF2005 geodetic reference ellipsoid, whereas the single-beam data were collected and processed in WGS84 (G1150)/ITRF00. Both datasets were subsequently transformed horizontally to NAD83 and then vertically to NAVD88, using the GEOID09 model, with NOAA VDatum version 3.2 transformation software (http://vdatum.noaa.gov/). The final x,y,z position data from each survey were merged to generate a digital elevation model with a cell-size resolution of 50 meters.
  1. How might this data set be cited?
    U.S. Geological Survey, 20131231, 50-Meter Digital Elevation Model of Coastal Bathymetry Collected in 2011 from the Chandeleur Islands, Louisiana (U.S. Geological Survey Field Activity Numbers 11BIM01 and 11BIM02):.

    Online Links:

    This is part of the following larger work.

    DeWitt, Nancy T., Pfeiffer, William R., Bernier, Julie C., Buster, Noreen A., Miselis, Jennifer L., Flocks, James G., Reynolds, B.J., Wiese, Dana S., and Kelso, Kyle W., 20131231, Coastal Bathymetry Data Collected in 2011 from the Chandeleur Islands, Louisiana: U.S. Geological Survey Data Series 848, U.S. Geological Survey, St. Petersburg, Florida.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.922837
    East_Bounding_Coordinate: -88.788992
    North_Bounding_Coordinate: 30.102033
    South_Bounding_Coordinate: 29.867495
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 02-Jun-2011
    Ending_Date: 16-Jun-2011
    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 516 x 250 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 meters
      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:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 0.1
      Altitude_Distance_Units: meters
      Altitude_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 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 June of 2011 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: 16-Jun-2011 (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 within about 15 km of the farthest single-beam trackline. GPS receivers recorded the 12-channel full-carrier-phase positioning signals (L1/L2) from satellites via the Thales choke-ring antenna. This GPS instrument combination was duplicated on the 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 DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Date: 16-Jun-2011 (process 2 of 9)
    Single-Beam Bathymetry Acquisition: The single-beam bathymetric data were collected aboard the 22-foot R/V TwinVee. Boat motion was recorded at 50-millisecond (ms) intervals using a Teledyne TSS Dynamic Motion Sensor (TSS DMS-05). HYPACK version 10, 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 using a Marimatech E-SEA-206 echosounder system with dual 208-kilohertz (kHz) transducers. 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, with each device string 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 DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Date: 16-Jun-2011 (process 3 of 9)
    Swath Bathymetry Acquisition: The interferometric swath bathymetry data were collected aboard the R/V SurveyCat using a SEA SWATHplus-M 234 kHz interferometric sonar system mounted on a sled attached to a rail system fastened between the catamaran hulls allowing the instrument to align directly below the GPS antennae in order to minimize geometry errors. Boat position and motion data were recorded in real time using 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 via the use of the 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 with positional and calibration offsets predefined by a session file (.sxs), allowing for real-time-corrected depths. Prior to deployment, all equipment offsets were surveyed in dry dock with the use of a laser total station. During the survey all swath tracklines were recorded in SEA raw data format (.sxr). A Valeport Mini Sound Velocity Sensor (SVS) was attached to the transducer mount and collected continuous 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 speed of sound profiles (water surface to seafloor) at intervals throughout the survey. 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
    Date: 01-Mar-2012 (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 also applied real-time motion corrections for heave, roll, and pitch to the vertical component of each position fix. The corrected positions were then 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 serves as both an acquisition software and initial processing software. Preliminary roll calibration trackline data were collected and processed using Systems Engineering and Assessment, Ltd. SWATHplus and Grid Processor software version 3.7.17. Instrument offset and calibrations values were input into the session file (.sxs), and the raw data files (.sxr) were then 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 is also written to the processed data file (.sxp), which can then be imported into advanced sounding data processing software such as CARIS HIPS and SIPS. 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. All processed data files were imported into CARIS HIPS and SIPS version 7.1, and the original sounding data were edited for outliers using the program's depth filters and reference surfaces. Any remaining outliers were then edited out manually. A CARIS BASE (Bathymetry with Associated Statistical Error) surface with associated CUBE (Combined Uncertainty and Bathymetry Estimator) sample surface was created from the edited soundings dataset. A BASE hypothesis is the estimated value of a grid node representing all the 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 subset editor. The x,y,z data were exported as ASCII text at a 5 x 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:
    • 11BIM01_IFB_ITRF05_xyz.txt
    Date: 01-Mar-2012 (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 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 the trajectories between the base to 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 the World Geodetic System of 1984 (WGS84) (G1150) geodetic datum. 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
    Date: 01-Jun-2012 (process 6 of 9)
    Single-beam Bathymetry Processing: The final DGPS positions exported from GrafNav were merged with the raw HYPACK files using the System for Accurate Nearshore Depth Surveying (SANDS), version 3.2. SANDS is a single beam acoustic (sounding) GPS-based hydrographic processing software developed by the USGS for shallow water bathymetric mapping (Hansen, 2008). Data were merged, geometrically corrected, and exported from SANDS in the originally acquired ellipsoid datum of WGS84 (G1150), which is equivalent to ITRF00. 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:
    • 11BIM02_SBB_ITRF00_xyz.txt
    Date: 01-Jun-2012 (process 7 of 9)
    Single-Beam Bathymetry Error Analysis: The processed single-beam data points were imported into ArcGIS, and an in-house Python script was created to evaluate the elevation differences at the intersection of crossing tracklines. The script calculates the elevation difference between points at each intersection using an inverse distance weighting equation. Elevation values at line crossings should not differ by more than the combined instrument acquisition error (manufacturer specified accuracies). GPS cycle slips, stormy weather conditions, and rough sea surface states may all contribute to poor data quality. If discrepancies were found that exceed the acceptable error threshold, then the line determined to be in error was either statically adjusted or removed. A line in error is considered to have one or more of the following: (1) a segment where several crossings are incomparable, (2) a known equipment problem, or (3) known bad GPS data seen in the post-processing steps. 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
    Date: 28-Apr-2013 (process 8 of 9)
    Datum transformation: Using the transformation software VDatum version 3.2, both the interferometric swath and single-beam x,y,z data were transformed horizontally from their data acquisition datums (swath, International Terrestrial Reference Frame of 2005, ITRF05; single-beam, ITRF00) to the North American Datum of 1983 (NAD83) reference frame and the North American Vertical Datum of 1988 (NAVD88) orthometric elevation 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 produced in this process:
    • 11BIM01_IFB_NAD83_NAVD88_GEOID09_xyz.txt 11BIM02_SBB_NAD83_NAVD88_GEOID09_xyz.txt
    Date: 28-Apr-2013 (process 9 of 9)
    Gridding Bathymetric data: Using ESRI ArcGIS version 10, the swath and the single-beam elevations were examined for spatial distribution and vertical agreement. After combining the datasets, a triangulated irregular network (TIN) was generated to provide unassuming linear predictions over data gaps in order to aid in the process of gridding the data into a raster layer or DEM. Converting the data points to a TIN surface also disallows any predictions outside the actual data extent. Using the natural neighbor algorithm in ArcGIS software, a DEM was generated at 50 x 50-m cell resolution. Finally, a low-pass raster-data filter was used to improve the uncertainty over data gaps between tracklines due to large trackline spacing relative to the swath width during acquisition, which is inherent to shallow water surveys over a large area. 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:
    • Chandeleurs_2011_50_NAD83_NAVD88_GEOID09_DEM.tif
  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 June, 2011. 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 the critical measurements are recorded manually and digitally and entered into their respective programs for calibration. Once calibration is complete and calibration status is considered acceptable, then survey operations commence. Each system has a dedicated computer, and efforts are made to utilize the same equipment and software versions on both systems. However, upgrades and changes occur and require additional setup, measurements, and notation. For the 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 Marimatech 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 8.10). 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 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 coordinates (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 0.00018 seconds latitude and 0.00045 seconds longitude. The 2-sigma (95%) horizontal accuracy of the OmniSTAR HP navigation used during swath bathymetry acquisition, as specified by OmniSTAR, is +/- 10 cm. The Coda Octopus F190R IMU, which integrates the OmniSTAR HP position with motion, measures vessel velocity (manufacturer's specified accuracy +/- 0.014 m/s), roll and pitch(+/- 0.025 degrees), heading (1 m baseline – 0.1 degrees), and heave (5 cm per meter of depth).
  3. How accurate are the heights or depths?
    All static base station sessions were processed through 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. For this survey, the maximum vertical error for the base station used for processing the single-beam bathymetry was +/- 2.1 cm. All single-beam soundings are post-processed to the base station coordinates. During single-beam acquisition, ship motion was measured using a TSS DMS-05 sensor which measures roll, pitch (manufacturer's specified accuracy +/- 0.05 degrees), and heave (5 percent of heave amplitude or 5 cm). During processing, the TSS measurements were used to geometrically correct the differentially corrected sounding positions. For the single-beam soundings, elevation differences at all trackline crossings were less than or equal to 14 cm, and the elevation differences were within +/- 10 cm for 99.3% of the 434 crossings at which the horizontal distance between soundings was less than 2 m. The 2-sigma (95%) vertical accuracy of the OmniSTAR HP navigation subscription used during swath bathymetry acquisition, as specified by OmniSTAR, is +/-15 cm. The Coda Octopus F190R IMU, which integrates the OmniSTAR HP position with motion, measures vessel velocity (manufacturer's specified accuracy +/- 0.014 m/s), roll and pitch (+/- 0.025 degrees), heading (1-m baseline – 0.1 degrees), and heave (5 cm per meter of depth). The vertical accuracy for the SWATHplus-M system varies with depth and across track range. At 57 m it is accurate to 10 cm vertically. The maximum vertical transformation error reported by VDatum for eastern Louisiana is 17.1 centimeters.
  4. Where are the gaps in the data? What is missing?
    This is a complete processed digital elevation model representing an interpolated bathymetric surface derived from the acoustic interferometric swath and single-beam data collected in June 2011 from around the northern Chandeleur Islands.
  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 June 2011. 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 were filled with 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 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 archive is provided in GeoTIFF format. To access these data, the user must have a GIS software package capable of reading .tif format.

Who wrote the metadata?

Dates:
Last modified: 08-Jun-2016
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/Chan11_DEM_metadata.faq.html>
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