Single-Beam Bathymetry Data 30-meter DEM Collected in 2015 from Grand Bay, Alabama/Mississippi

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Frequently anticipated questions:


What does this data set describe?

Title:
Single-Beam Bathymetry Data 30-meter DEM Collected in 2015 from Grand Bay, Alabama/Mississippi
Abstract:
As part of the Sea level and Storm Impacts on Estuarine Environments and Shorelines project (SSIEES), scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center conducted a single-beam bathymetry survey within the estuarine, open bay and tidal creek environments of Grand Bay Alabama/Mississippi, in May-June 2015. The goal of the SSIEES project is to assess the physical controls of sediment and material exchange between wetlands and estuarine environments along the northern Gulf of Mexico, specifically Grand Bay MS/AL and Vermilion Bay, Louisiana, as well as along the US east coast in Chincoteague Bay Virginia/Maryland. The data described in this report will provide baseline bathymetric information for future research investigating wetland/marsh evolution, sediment transport, recent and long term geomorphic change, and will support modeling of future changes in response to restoration and storm impacts. The survey area encompasses more than 40 square kilometers (km2) of Grand Bay?s incorporated waters. This data release archives processed single-beam bathymetry data, collected from May 28-June 3, 2015 (USGS Field Activity Number 2015-315-FA). Geographic information system data products include: a 10 and 30-meter cell size interpolated bathymetry grid, trackline maps, and point data files. Additional files include error analysis maps, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FGDC) metadata.
Supplemental_Information:
This record serves as a comprehensive archive for the final Digital Elevation Model (DEM) created by the use of all single-beam bathymetry data collected under the FAN (2015-315-FA) which encompasses data from 2 separate survey platforms; RV Shark (15CCT04), and RV Chum (15CCT05). The single-beam bathymetry corrected position was 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 NAD83 using GEOID12A as well as NAD83 Mean Low Lower Water (MLLW) (NOAA NGS VDatum software 3.2 - http://vdatum.noaa.gov/). The Final x,y,x position point data was gridded at a 30-meter cell size resolution to create the digital elevation model which represents elevations from -0.01 to -3.62 meters.
  1. How might this data set be cited?
    U.S. Geological Survey, 20161122, Single-Beam Bathymetry Data 30-meter DEM Collected in 2015 from Grand Bay, Alabama/Mississippi:.

    Online Links:

    This is part of the following larger work.

    DeWitt, Nancy T., Stalk, Chelsea A., Smith, Christopher G., Locker, Stanley D., Fredericks, Jake J., McCloskey, Terrance A., and Wheaton, Cathryn J., 20171201, Single-Beam Bathymetry Data Collected in 2015 from Grand Bay, Alabama-Mississippi: U.S. Geological Survey Data Series 1070, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.412969
    East_Bounding_Coordinate: -88.311205
    North_Bounding_Coordinate: 30.409530
    South_Bounding_Coordinate: 30.340547
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 28-May-2015
    Ending_Date: 03-Jun-2015
    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 251 x 323 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
      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 30
      Ordinates (y-coordinates) are specified to the nearest 30
      Planar coordinates are specified in meter
      The horizontal datum used is NAD83 North American Datum 1983.
      The ellipsoid used is MLLW.
      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: MLLW
      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?
    U.S. Geological Survey
    Attn: Nancy T. DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

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

Why was the data set created?

This 30-meter cell size digital elevation model is an interpretive product that was derived from the processed single-beam bathymetry data collected in May-June 2015 within Grand Bay Alabama/Mississippi.

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 4)
    DGPS Navigation Processing: The Geographic Positioning System (GPS) base stations were occupied by USGS personnel for the purpose of this survey. Bench mark B166 was located to the north-north west of the survey area near the railroad tracks at the entrance of the Grand Bay National Estuarine Research Reserve (GBNERR), 189A was located north-north west of the survey area at the boat launch location used for this survey). The base stations were 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 0.1 seconds (s). GPS instrumentation was duplicated on both survey vessels (rovers); however, an Ashtech Global Navigation Satellite Systems (GNSS) antenna was used instead of Choke-ring antennas. The base receivers and rover receivers recorded positions concurrently at all times throughout the survey. Rovers RV Shark and RV Chum recorded data every 0.1 s throughout the survey. The coordinate values for each of the GPS base stations (B166,189A) 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 (s), 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. 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 (0.1-s for 15CCT04, 15CCT05), 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:
    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: 2015 (process 2 of 4)
    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 was scanned using the Navigation Editor allowing 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 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 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 including position, depth, GPS tide, and Speed of Sound (SOS), were then merged and geometrically corrected in CARIS to produce processed x,y,z point data. Once merged the dataset is reviewed for erroneous points using the Single Beam Editor. The points that are visually obvious are often related to cavitation in the water column obscuring the fathometer signal, tight turns at the marsh face affecting the tracking of the incoming GPS signal, and/or false readings due to general equipment issues. Data showing these issues 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 on shoals or within seagrass beds were reviewed against the surrounding data for overall consistency. Finally, a Bathymetry with Associated Statistical Error (BASE) surface was created. Using the Subset Editor, the BASE surface was used as a color coded guide to pinpoint crossings that are visually offset from one another. If an offset was identified, it was further examined and was 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 combined single-beam bathymetry datasets (15CCT04 and 15CCT05) consists of 3,844,122 x,y,z data points with an ellipsoidal height range of -33.364 m to -29.531 m. 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)
    cstalk@usgs.gov
    Data sources produced in this process:
    • Grand_Bay_2015_SBB_Level_05_ITRF00.txt
    Date: 2015 (process 3 of 4)
    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 0.5-m color coded intervals. First all data were visually scanned for any obvious outliers or problems. Then, the data were run through an in-house script created in Visual Basic (Crossing program Version 3.2). The script was created 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. Elevation values at line crossings should not differ by more than the combined instrument acquisition error (per manufacturer specified accuracies). 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. The script was run on all vessel point data first on a vessel by vessel basis and then run a final time with both vessels collectively by use of a merged shape file with all point data (Grand_Bay_2015_SBB_Level_05_xxx_ITRF00). Once all data were found to be final, the single-beam bathymetric data were transformed horizontally and vertically from their data acquisition datum WGS84 (ITRF00) to the North American Datum of 1983 (NAD83) reference frame using the National Geodetic Survey (NGS) geoid model of 2012A (GEOID12A) as well as North American Datum of 1983 (NAD83) Mean Lower Low Water, using the transformation software VDatum version 3.2. The MLLW x,y,z data points were written into a ASCII format and considered to be the final values. 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
    Data sources used in this process:
    • 2015-315-FA_SBB_Level_03_xxx_ITRF00.txt
    Data sources produced in this process:
    • Grand_Bay_2015_SBB_Level_05_xxx_NAD83_NAVD88_GEIOD12A.txt Grand_Bay_2015_SBB_Level_05_xxx_NAD83_UTM16N_MLLW.txt
    Date: 2015 (process 4 of 4)
    Gridding Bathymetric data and computing grid error: The single-beam soundings were imported into ESRI?s ArcMap version 10.2 and gridded using Spatial Analyst tools "create TIN," "TIN to raster," and "extract by raster mask." First a bounding polygon representing the extent of survey tracklines was created and converted into a raster mask using the ArcGIS "polygon to raster" tool. Next, the final point data were created into a TIN using the "create TIN" and then the data were converted into a raster DEM by use of the "TIN to raster tool" using the natural neighbor function with a cell size of 30 m. Finally the interpolated DEM is clipped to the survey extent by use of the "extract by mask" tool using the raster mask created first in this process. The final product is a DEM of the entire survey extent. The grid range values were from -0.01 m maximum to -3.62 m minimum. In order to evaluate how well the final DEM represents the final sounding data both spatially and quantitatively a comparison of the DEM versus the sounding (x,y,z point data) was plotted in ArcGIS by use of 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. By use of the generated shape file and associated attribute table, the root mean square (RMS) error, quantified as the difference between the measured depth and the grid depth values, was calculated. The overall RMS Error in meters is 0.07. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nanacy T. DeWitt
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    ndewitt@usgs.gov
    Data sources used in this process:
    • Grand_Bay_2015_SBB_NAD83_MLLW.txt
    Data sources produced in this process:
    • Grand_Bay_2015_NAD83_MLLW_30m_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. 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 Ashtech as +/-10 mm for Kinematic surveying. The horizontal positional accuracy values for latitude and longitude are -0.00000134 to +0.00000134 and -0.0000019 to +0.0000019 decimal degrees, respectively.
  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 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 dataset is considered complete for the information presented, as described in the abstract section. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    The single beam bathymetry data were collected during one research cruise in May 28-June 3, 2015 (2015-315-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 30-meter; data gaps between acquisition tracklines are predicted values generated by the gridding algorithm - natural neighbors.

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: None
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    Attn: Nancy T. 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? Grand_Bay_2015_NAD83_MLLW_30m_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. To utilize this data, the user must have a GIS software package capable of reading .tif format.

Who wrote the metadata?

Dates:
Last modified: 07-Aug-2018
Metadata author:
Cherokee Nation Technologies/U.S. Geological Survey
Attn: Chelsea A Stalk
Researcher I
600 4th Street South
St. Petersburg, FL
USA

727-502-8000 (voice)
cstalk@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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