October 2015 bathymetry collected near Dumbarton Bridge in south San Francisco Bay, California

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Frequently anticipated questions:

What does this data set describe?

Title:
October 2015 bathymetry collected near Dumbarton Bridge in south San Francisco Bay, California
Abstract:
Bathymetric survey data were collected in October 2015 just south of Dumbarton Bridge in south San Francisco Bay, California. Portions of the main channel and western shallows/intertidal mudflats were surveyed using an interferometric sidescan sonar system following procedures detailed in Foxgrover and others, 2011. The bathymetry is provided as a 1-m resolution raster in geoTIFF format, referenced to the vertical datum of mean lower low water (MLLW). To convert to the North American Vertical Datum of 1988 (NAVD88), subtract a static offset of 0.37 m (datum conversions provided in Foxgrover and others, 2007).
Supplemental_Information:
Additional information about the field activity from which these data were derived is available online at: https://cmgds.marine.usgs.gov/fan_info.php?fan=2015-669-FA
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in Esri format, this metadata file may include some Esri-specific terminology.
  1. How might this data set be cited?
    Foxgrover, Amy C., Jaffe, Bruce E., and Fregoso, Theresa A., 20220701, October 2015 bathymetry collected near Dumbarton Bridge in south San Francisco Bay, California: data release DOI:10.5066/P9BIB67S, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Foxgrover, Amy C., Jaffe, Bruce E., and Fregoso, Theresa A., 2022, Bathymetric surveys collected near Dumbarton Bridge in south San Francisco Bay, California, 2008 to 2019: data release DOI:10.5066/P9BIB67S, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -122.125675
    East_Bounding_Coordinate: -122.108154
    North_Bounding_Coordinate: 37.506598
    South_Bounding_Coordinate: 37.491106
  3. What does it look like?
    DB_Oct2015_bathy.png (PNG)
    A shaded relief image of the October 2015 bathymetric survey with 10X vertical exaggeration to accentuate the tidal flat and channel morphology.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 13-Oct-2015
    Currentness_Reference:
    ground condition at time data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data set
  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 1704 x 1532, 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: 10
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000
      False_Northing: 0.0
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1.0
      Ordinates (y-coordinates) are specified to the nearest 1.0
      Planar coordinates are specified in meters
      The horizontal datum used is North American Datum of 1983 (NSRS2007).
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: Mean Lower Low Water (MLLW)
      Altitude_Resolution: 0.01
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method: Attribute values
  7. How does the data set describe geographic features?
    Altitude
    Elevation relative to MLLW in meters. Values are positive up. (Source: Producer defined)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Amy C. Foxgrover
    • Bruce E. Jaffe
    • Theresa A. Fregoso
  2. Who also contributed to the data set?
    Funding was provided by the U.S. Geological Survey, California Coastal Conservancy, U.S. Environmental Protection Agency, the Resources Legacy Fund, and Santa Clara Valley Water District.
  3. To whom should users address questions about the data?
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Attn: PCMSC Science Data Coordinator
    2885 Mission Street
    Santa Cruz, CA

    831-427-4747 (voice)
    pcmsc_data@usgs.gov

Why was the data set created?

In 2008 the USGS began mapping the main channel and shallow intertidal mudflats between the Dumbarton Bridge and a railroad bridge located 1 km to the south in south San Francisco Bay. This information was collected to document bathymetric change before and after restoration to inform the South Bay Salt Pond Restoration Project (https://www.southbayrestoration.org), which initiated the restoration of a former salt pond (SF2) on the western shore in 2010. In 2011, following the collection of eight bathymetric surveys, funding for this site-specific project came to an end, yet the location remained an instrumentation calibration site for ongoing research in Alviso Slough (Foxgrover and others, 2011). The calibration surveys collected near the Dumbarton Bridge resulted in an additional eight surveys, collected primarily in the main channel, from 2013 to 2019.

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 6)
    Sonar Data Collection. Bathymetry data were collected using a 234.5 kHz SEA (Systems Engineering and Assessment Ltd.) SWATHplus-M phase-differencing sidescan sonar. The sonar was pole-mounted on the 34-foot USGS mapping vessel R/V Parke Snavely and affixed to a hull brace. GPS position data were passed through an Applanix Position and Motion Compensation System for Marine Vessels POS/MV inertial measurement unit (IMU) to the sonar hardware and data-collection software. Sonar heads, GPS antennae, and the IMU were surveyed in place to a common reference frame with a Geodimeter 640 Total Station. The R/V Parke Snavely was outfitted with three networked workstations and a navigation computer for use by the captain and survey crew for data collection and initial processing.
    Date: 2015 (process 2 of 6)
    Vessel Position and Attitude. An Applanix Position and Motion Compensation System for Marine Vessels (POS/MV) was used to accurately determine the position of the survey vessel. The POS/MV utilizes Global Navigation Satellite System (GNSS) data in combination with angular rate and acceleration data from the IMU and heading data from the GPS Azimuth Measurement Systems (GAMS) to produce accurate position and orientation information through a virtual network of base stations. As opposed to receiving high-accuracy Real-Time Kinematic (RTK) corrections, the POS records raw inertial and GNSS data while surveying, which are later refined through post processing to incorporate publicly available GPS data from nearby base stations. During post processing the POS/MV data is run through POSPac software to produce a Smoothed Best Estimate of Trajectory (SBET) file, which is then imported back into Swath Processor to produce high-accuracy positions relative to the WGS84 ellipsoid. The RMS results from our POS/MV surveys show positional errors of less than 5 cm in X, Y, and Z.
    Date: 2015 (process 3 of 6)
    Sound Velocity Measurements. Sound velocity measurements were collected continuously with an Applied Micro Systems Micro SV deployed on the transducer frame for real-time sound velocity adjustments at the transducer-water interface. The Micro SV is accurate to +/- 0.03 m/s. In addition, sound velocity profiles (SVP) were collected with an Applied MicroSystems, SvPlus 3472. This instrument provides time-of-flight sound-velocity measurements by using invar rods with a sound-velocity accuracy of +/- 0.06 m/s, pressure measured by a semiconductor bridge strain gauge to an accuracy of 0.15 percent (Full Scale) and temperature measured by thermistor to an accuracy of 0.05 degrees Celsius (Applied Microsystems Ltd., 2005).
    Date: 2015 (process 4 of 6)
    Sonar Sounding Processing. GPS data and measurements of vessel motion (heave, pitch, and roll) were combined in the POS/MV hardware to produce a high-precision vessel attitude packet. This packet was transmitted to the Swath Processor acquisition software in post-processing and combined with instantaneous sound velocity measurements at the transducer head before each ping. Up to 20 pings per second were transmitted with each ping consisting of 2048 samples per side (port and starboard). The returned samples were projected to the seafloor using a ray-tracing algorithm working with the previously measured sound velocity profiles in SEA Swath Processor (version 3.12.7). A series of statistical filters were applied to the raw samples to isolate the seafloor returns from other uninteresting targets in the water column. Finally, the processed data were stored line-by-line in both raw (.sxr) and processed (.sxp) trackline files.
    Date: 2016 (process 5 of 6)
    Digital Elevation Model Production. The raw bathymetry data were filtered in SEA Swath Processor (version 3.12.7) and imported into CARIS HIPS and SIPS (version 9.1) for post-processing. Within CARIS a swath angle BASE (Bathymetric with Associated Statistical Error) surface was created at 1-m resolution and the subset editor used to manually eliminate any remaining outliers or artifacts. The average depth within each 1 by 1 m cell was exported as an ASCII text file and imported into Surfer (version 10) for interpolation using a linear kriging algorithm with a 1-simga nugget of 0.07 m and a 5 by 5 m search radius. The resultant grid was exported to ESRI ArcMap (version 10.7.1) for display and further analyses.
    Date: 2021 (process 6 of 6)
    Datum Conversions. To convert the bathymetry from WGS84 ellipsoid heights to the tidal datum of MLLW the data were first transformed from WGS84(ITRF2000) to the NAD83(CORS96) ellipsoid using a 14-point Helmert transformation described by Soler and Snay (2004) using the command line tool CS2CS in the Proj4 library (http://trac.osgeo.org/proj/). A fixed Geoid09 offset of -32.58 m was then applied to convert the NAD83 ellipsoid heights to orthometric heights NAD83(CORS96)/NAVD88. The orthometric NAVD88 elevations were converted to MLLW (1983–2001 tidal epoch) by adding 0.37 m to the surface, the conversion provided by the CO-OPS division of NOAA for a 2005 bathymetric survey of south San Francisco Bay (Foxgrover and others, 2007).
  3. What similar or related data should the user be aware of?
    Foxgrover, Amy C., Finlayson, David P., Jaffe, Bruce E., and Fregoso, Theresa A., 2011, Bathymetry and digital elevation models of Coyote Creek and Alviso Slough, south San Francisco Bay, California (Version 5.0, June 2020): Open-File Report 2011-1315, U.S. Geological Survey, Reston, VA.

    Online Links:

    Foxgrover, Amy C., Jaffe, Bruce E., Hovis, Gerald T., Martin, Craig A., Hubbard, James R., Samant, Manoj R., and Sullivan, Steve M., 2007, 2005 Hydrographic Survey of South San Francisco Bay, California: Open-File Report 2007-1169, U.S. Geological Survey, Reston, VA.

    Online Links:

    Ltd., Applied Microsystems, 2005, SVplus sound velocity, temperature, and depth profiler user's manual.

    Other_Citation_Details:
    Applied Microsystems Ltd., 2005, SVplus sound velocity, temperature, and depth profiler user's manual, ver. 1.23, https://amloceanographic.com/.
    Soler, T., and Snay, R.A., 2004, Transforming positions and velocities between the International Terrestrial Reference Frame of 2000 and North American Datum of 1983.

    Other_Citation_Details:
    Soler, T., and Snay, R.A., 2004, Transforming positions and velocities between the International Terrestrial Reference Frame of 2000 and North American Datum of 1983: Journal of Surveying Engineering, v. 130, no. 2, https://doi.org/10.1061/(ASCE)0733-9453(2004)130:2(49)

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    These bathymetric data have not been independently verified for accuracy.
  2. How accurate are the geographic locations?
    Uncertainty in the horizontal position of each sounding is a function of the total uncertainty propagated through each of the following component instruments: 1) base station GPS, 2) vessel GPS, 3) inertial motion unit (IMU), 4) water sound velocity model, and 5) beam spreading in the water column. The RMS results from POS/MV surveys show vessel positional errors of less than 5 cm in the X and Y. Assuming no systematic errors in the measurement instruments themselves, beam spreading is the dominate source of positional uncertainty. The 1-degree sonar beam of the SWATHplus-M results in horizontal uncertainty ranging from 0.10 m at 10 m slant range, to about 0.45 m at 50 m slant range.
  3. How accurate are the heights or depths?
    The RMS results from POS/MV surveys show vertical positional errors of the survey vessel to be less than 5 cm. For relatively flat regions, the standard deviation of sounding elevations within each 1 m by 1 m cell is a good representation of survey precision. After filtering the data to remove obvious outliers, the standard deviation of the remaining sounding elevations was calculated for each cell (each containing tens of soundings) in CARIS. The mean standard deviation on the intertidal flats is 4 cm and below MLLW, where actual variability in slope influences the values, the average standard deviation is 10 cm. When possible, an additional assessment of survey accuracy was conducted by analyzing sounding values at the intersection of perpendicular trackline crossings. The mean difference of trackline crossing on the intertidal flats 2 cm (SD = 4) matched that of the channel and channel margin (depths below MLLW) but with increased spread in the data, 2 cm (SD = 10).
  4. Where are the gaps in the data? What is missing?
    Dataset is considered complete for the information presented, as described in the abstract. 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?
    All bathymetric values are derived from the same instruments and processing workflow. No formal logical accuracy tests were conducted.

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 USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. This information is not intended for navigation purposes.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - CMGDS
    2885 Mission Street
    Santa Cruz, CA

    1-831-427-4747 (voice)
    pcmsc_data@usgs.gov
  2. What's the catalog number I need to order this data set? These data are available in GeoTIFF format, including a tif world file (.tfw) and CSDGM FGDC-compliant metadata.
  3. What legal disclaimers am I supposed to read?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: Downloadable zip file contains the TIFF (.tif), and the tif world file (.tfw). in format GeoTIFF (version ArcGIS 10.7.1) Size: 0.9
      Network links: https://doi.org/10.5066/P9BIB67S
    • Cost to order the data: None.

  5. What hardware or software do I need in order to use the data set?
    The downloadable data file has been compressed with the "zip" command and can be unzipped with Winzip (or other tool) on Windows systems. To utilize these data, the user must have software capable of uncompressing the WinZip file and importing and viewing a GeoTIFF file.

Who wrote the metadata?

Dates:
Last modified: 01-Jul-2022
Metadata author:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Attn: PCMSC Science Data Coordinator
2885 Mission Street
Santa Cruz, CA

831-427-4747 (voice)
pcmsc_data@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/DataReleases/CMGDS_DR_tool/DR_P9BIB67S/DB_Oct2015_MLLW_bathy_metadata.faq.html>
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