MGL1109backsgeo.asc: Multibeam backscatter data collected by the U.S. Geological Survey in the Gulf of Alaska in 2011 during cruise MGL1109, 100-meter gridded data in Esri gridascii format, geographic coordinate system

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Frequently anticipated questions:

What does this data set describe?

Title:
MGL1109backsgeo.asc: Multibeam backscatter data collected by the U.S. Geological Survey in the Gulf of Alaska in 2011 during cruise MGL1109, 100-meter gridded data in Esri gridascii format, geographic coordinate system
Abstract:
This raster dataset represents approximately 69,060 square kilometers of Simrad EM122 multibeam-backscatter data collected in the Gulf of Alaska during U.S. Geological Survey (USGS) cruise MGL1109 aboard the R/V Marcus G. Langseth. The data have been reduced for position, elevation, orientation, water-column sound-speed, and refraction effects.
Supplemental_Information:
Additional information about the USGS field activities from which these data were derived is available online at:
https://cmgds.marine.usgs.gov/fan_info.php?fan=L0911GA https://cmgds.marine.usgs.gov/fan_info.php?fan=2011-034-FA
Additional information about the Lamont-Doherty field activities from which these data were derived is available online at:
https://www.rvdata.us/search/cruise/MGL1108 https://www.rvdata.us/search/cruise/MGL1109
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?
    Barth, Ginger, Baldwin, Wayne E., Reece, Robert S., Gulick, Sean S., Danforth, William W., and Wong, Florence L., 20220825, MGL1109backsgeo.asc: Multibeam backscatter data collected by the U.S. Geological Survey in the Gulf of Alaska in 2011 during cruise MGL1109, 100-meter gridded data in Esri gridascii format, geographic coordinate system: data release DOI: 10.5066/F7HM56HK, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Barth, Ginger, Baldwin, Wayne E., Reece, Robert S., Gulick, Sean S., Danforth, William W., and Wong, Florence L., 2022, Multibeam bathymetry and acoustic backscatter data from the Alaskan region, Extended Continental Shelf Project, 2011 field season: Gulf of Alaska and Bering Sea: data release DOI: 10.5066/F7HM56HK, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -152.381751
    East_Bounding_Coordinate: -137.797038
    North_Bounding_Coordinate: 57.713119
    South_Bounding_Coordinate: 48.268275
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/560ef844e4b0ba4884c5ed1e?name=MGL1109backscat.jpg&allowOpen=true (JPEG)
    MGL1109 acoustic backscatter, Gulf of Alaska
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 03-Jun-2011
    Ending_Date: 25-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 9559 x 16898 x 1, type Grid Cell
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.001. Longitudes are given to the nearest 0.001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is D_WGS_84.
      The ellipsoid used is WGS_84.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    Attribute Table
    Table containing attribute information associated with the data set. (Source: Producer defined)
    Value
    backscatter intensity (Source: Producer defined)
    Range of values
    Minimum:-59.610
    Maximum:7.790
    Units:decibel
    Entity_and_Attribute_Overview: 
    
 Cell Size =             0.001 degree
 Data Type:            Floating Point
 Number of Rows    =       9559
 Number of Columns =       16898

 BOUNDARY (WGS84, excluding NODATA):
 Xmin = -152.382
 Xmax = -137.797
 Ymin =  48.268
 Ymax = 57.713

 BOUNDARY (converted from UTM zone 6 coordinates)
 Xmin = -152.555
 Xmax = -135.657
 Ymin =  48.256
 Ymax = 57.815

 STATISTICS (decibels)

 Minimum Value =            -59.610
 Maximum Value =              7.790
 Mean          =            -27.752
 Standard Deviation =         2.751

 COORDINATE SYSTEM DESCRIPTION

 Projection           GEOGRAPHIC
 Datum                     WGS84
 Units                        DD
 Spheroid                  WGS84
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information was generated by the individual and/or agency identified as the originator of the data set. Please review the rest of the metadata record for additional details and information.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Ginger Barth
    • Wayne E. Baldwin
    • Robert S. Reece
    • Sean S. Gulick
    • William W. Danforth
    • Florence L. Wong
  2. Who also contributed to the data set?
  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 June 2011, the U.S. Geological Survey (USGS) conducted a research cruise in the Gulf of Alaska aboard the R/V Marcus G. Langseth (Lamont-Doherty Earth Observatory, Columbia University) as part of the U.S. Extended Continental Shelf Project. The mission focused primarily on obtaining geophysical data (multichannel and CHIRP seismic reflection, ocean bottom seismometry, multibeam bathymetry, sonobuoy, XBT and XCTD) for the purposes of determining geologic framework, crustal nature, and sediment thickness in support of delineating the U.S. Extended Continental Shelf under provisions contained in Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS).

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: Jun-2011 (process 1 of 5)
    Multibeam bathymetry and backscatter data were collected using a 12 kHz Kongsberg Simrad EM-122 multibeam echosounder and SIS (v3.8.2) acquisition software. The system consists of two hull-mounted transducer arrays, a transmit unit (150 deg. x 1 deg.) located along the ship centerline, and a receive unit (1 deg. x 30 deg.) that is abaft and oriented athwart-ships. The transducer pod is tilted 4 degrees towards the bow to reduce noise from cavitation and bubbles. The system forms a swath of 288 beams that produce an across-track profile of 432 soundings. The SIS software processes range/angle data from each ping during acquisition, merging position, inertial-motion, and sound-velocity data to derive a solution for vessel motion and raybending, and calculate sounding depths and positions. Sound velocity information entered into SIS was obtained from the Applied Micro Systems Micro SV mounted on the transducer pod and 52 XBT profiles. XBT profiles were extended to 12 km depth with data generated by the unix program 'mblevitus', a module of the multibeam processing package MB-System (Caress and Chayes, 2006). Average water column salinity of 34.4 ppt was determined by extrapolating data from XCDT casts. Multibeam data were collected nearly continuously throughout the cruise, effectively mapping the seafloor along the course of the ship's track. Beam angle was set at 70 on each side throughout the program and swath widths were generally between 3 and 4 times water depth. SIS logged bathymetry and backscatter solutions to the Simrad '.all' format for archival purposes.
    Date: Aug-2012 (process 2 of 5)
    EM122 backscatter was processed and mosaicked using the FMGeocoder module in IVS Fledermaus. The Automatic Processing option (Mosaic only) was utilized with the EM122 Beam Time Series (from *.all raw files) selected as the backscatter source. A single tile mosaic, with 100 m per pixel resolution, was created for the entire survey area. The final mosaic was exported to these file formats: Fledermaus SD, ESRI ASCII Raster, and XYB format (Easting, Northing, dB value).
    The following project setup and processing parameters were specified: Project Coordinate System: Horiz. CS: WGS84,UTM,Zone 6N Custom Survey Area: XMIN,YMIN,XMAX,YMAX = 169100, 5385700, 1181500, 6408000 EM122 Sensor Config: Tx1:Xoff,Yoff,Zoff,Roff,Poff,Yoff = 20.92,0.57,8.46,0.16,-0.08,359.99 Tx2:Xoff,Yoff,Zoff,Roff,Poff,Yoff = 16.07,0.05,8.53,0.16,-0.08,0 IMU:Xoff,Yoff,Zoff,Roff,Poff,Yoff,lat = 0,0,0,-0.51,-0.23,0.43,0 Line Processing Parameters: Backscatter: Apply Beam Pattern Correction Beam Angle Cutoffs: start,cut = 0, 90 Backscatter Range: Calibrated,Min,Max = -70,10 AVG: Apply AVG - Flat Algorithm - Window Size 30 Statistics: Log space (dB) Navigation: Linear Interp. Format: Kongsberg(.all) Navigation Src.: Use Default Dual Swath Comp.: First O Sonar Defaults: Default Vals - Custom Override All - Sonar Type: Simrad EM122 MBES PrimFrq,SecFrq,MAN,MNB,ATBW,CTBW,SSS = 12000,0,120,484,2,4,1500 PusleL,PSR,SSR,Spread,TxPwr,RecGain,Abs = 5000,1001,0,0,1,1,30 Mosaicking Parameters: Line Blending = 50 percent Style, FiltType = Blend,dB Mean Person who carried out this activity:
    U.S. Geological Survey
    Attn: Wayne E. Baldwin
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    508-457-2226 (voice)
    wbaldwin@usgs.gov
    Date: Aug-2012 (process 3 of 5)
    The output ESRI ASCII Raster file was imported as a floating point grid into ArcGIS 9.3 using the ASCII to Raster tool selected from the Conversion Tools - To Raster toolbox. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Wayne E. Baldwin
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    508-457-2226 (voice)
    wbaldwin@usgs.gov
    Date: 18-Oct-2012 (process 4 of 5)
    Wrote version 1 of metadata. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Wayne E. Baldwin
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    508-457-2226 (voice)
    wbaldwin@usgs.gov
    Date: 17-Aug-2022 (process 5 of 5)
    Metadata was modified to bring up to current USGS PCMSC standards. Point of Contact and Metadata Contact information was updated. Keywords were added and refined. Cross Reference citation added. Details about different Network Resource Name links was given in the Access Instructions section. Minor typos were corrected. No data information was changed. Person who carried out this activity:
    Susan A Cochran
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Geologist
    2885 Mission St.
    Santa Cruz, CA
    United States

    831-460-7545 (voice)
    scochran@usgs.gov
  3. What similar or related data should the user be aware of?
    Caress, David W., and Chayes, Dale N., 2006, MB-System source code.

    Online Links:

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

  1. How well have the observations been checked?
    Kongsberg-Simrad EM122 Multibeam Echosounder was used with transmit (fore-aft) and receive (athwart ships) beam widths of 1 degree, with swaths of 3-4 times water depth in water depths between 50 and 6000 m. Depth accuracies not determined, however Kongsberg-Simrad state that the system is capable of depth accuracies approaching 0.2 percent of water depth.
  2. How accurate are the geographic locations?
    Horizontal positioning of the vessel was determined using a Kongsberg Seapath 300 series integrated inertial motion and positioning system. Positioning is accurate to better than 5 meters (at 95 percent confidence) during all surveying. All positioning is referenced to the WGS84 Datum.
  3. How accurate are the heights or depths?
    No attempt was made to determine the accuracy of the system although recorded depths are typically within +/-10 m of the center-beam multibeam sounding.
  4. Where are the gaps in the data? What is missing?
    Raw EM122 Multibeam Echosounder data collected during OBS operations were not used in the generation of this gridded dataset because OBS instruments were deployed along transects coincident with previously surveyed ship track. Upon inspection in CARIS during post-processing it was deemed appropriate to exclude the redundant data from the gridding process.
  5. How consistent are the relationships among the observations, including topology?
    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 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 - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? These data are available in ASCII GRID format, along with 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?

Who wrote the metadata?

Dates:
Last modified: 25-Aug-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/ScienceBase/DR_F7HM56HK/MGL1109backsgeo.asc.faq.html>
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