2-m resolution backscatter grid of Tomales Bay, California (TOMALESAMPG)

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Frequently-anticipated questions:

What does this data set describe?

Title:
2-m resolution backscatter grid of Tomales Bay, California (TOMALESAMPG)
Abstract:
The SWATHplus interferometric sidescan stores backscatter amplitude with each bathymetric sounding. This amplitude data can be plotted to produces an acoustic image of the sea floor. Cell values in the image represent the relative strength of the acoustic signal returned (backscattered) to the transducer off of the sea bed. A cell value equal to 1.0 is an average strength return, cell values above 1.0 are relatively stronger than average; values less than 1 are below average strength returns.

The Tomales Bay backscatter amplitude grid is composed of data from two interferometric sidescansonar surveys collected in November 2004 and November 2005 (USGS activities F-1-04-TB, F-2-05-TB).

This metadata record describes the Tomales Bay grid exported as

1. ESRI ASCII grid format (includes nodata -9999 values) 

 ncols         5442
 nrows         7069
 xllcorner     501421
 yllcorner     4218273
 cellsize      2
 NODATA_value  -9999
 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999
 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999
 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 0 0 0 0 0 0
2. x-y (decimal degrees) and z (strength of acoustic return relative to mean value) data (nodata excluded). 

 -122.98290,38.23969,0.000
 -122.98288,38.23969,0.000
 -122.98286,38.23969,0.000
 -122.98284,38.23969,0.000
 -122.98282,38.23969,0.000
 -122.98280,38.23969,0.000
 -122.98278,38.23969,0.000
 -122.98292,38.23967,1.315
 -122.98290,38.23967,1.346
Supplemental_Information:

Additional information about the field activities from which this data set was derived are available online at 

<http://walrus.wr.usgs.gov/infobank/f/f104tb/html/f-1-04-tb.meta.html>
<http://walrus.wr.usgs.gov/infobank/f/f205tb/html/f-2-05-tb.meta.html>
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 ArcInfo format, this metadata file may include some ArcInfo-specific terminology.

  1. How should this data set be cited?

    Anima, Roberto J. , Chin, John L. , Finlayson, David P. , McGann, Mary L. , and Wong, Florence L. , 2007, 2-m resolution backscatter grid of Tomales Bay, California (TOMALESAMPG): USGS Open-File Report USGS OFR 2007-xxxx, U.S. Geological Survey, Menlo Park, California.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.98379025
    East_Bounding_Coordinate: -122.85938895
    North_Bounding_Coordinate: 38.23970089
    South_Bounding_Coordinate: 38.11219761

  3. What does it look like?

    <https://pubs.usgs.gov/of/2008/1237/images/tomalesg.jpg> (gif or jpg)
    preview image of report

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 2006
    Currentness_Reference: Ground Condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: map

  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 7069 x 5442, 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: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000
      False_Northing: 0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 2.0
      Ordinates (y-coordinates) are specified to the nearest 2.0
      Planar coordinates are specified in Meters

      The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.98.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview: 

    
TOMALESAMPG.STA:

 backscatter amplitude relative to a mean value of 1.0

COLUMN   ITEM NAME        WIDTH OUTPUT  TYPE N.DEC  ALTERNATE NAME
    1  MIN                    8    15     F      3
    9  MAX                    8    15     F      3
   17  MEAN                   8    15     F      3
   25  STDV                   8    15     F      3

 MIN             MAX            MEAN            STDV
 0.000           1.768           1.003           0.073
    Entity_and_Attribute_Detail_Citation: none

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    Florence L. Wong
    United States Geological Survey (USGS)
    Geologist, GIS Coordinator
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561
    USA

    (650) 329-5327 (voice)
    (650) 329-5190 (FAX)
    fwong@usgs.gov

Why was the data set created?

These data are intended for science researchers, students, policy makers, and the general public. The data can be used with geographic information systems (GIS) software to display geologic and oceanographic information.

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: 2007 (process 1 of 2)
    Swath bathymetry and backscatter. Swath bathymetry and backscatter for the northern and central portions of Tamales Bay (cruise F-1-04-TB and F-2-05-TB) were collected using a pole-mounted, SEA Inc., 234 kHz, SWATHplus interferometric sidescan sonar system. Attitude compensation and vessel positioning were provided by a CodaOctopus F180 attitude and positioning system. Sound velocity profile measurements were collected with an Applied Micro Systems, SvPlus 3472.

    The horizontal datum of the surveys was established by differential GPS using the WGS84 ellipsoid.

    Raw bathymetry and amplitude data were collected using the Swath Processor software provided with the sonar system.

    The first step in the acoustic data processing applies an empirical gain function to the raw soundings to counteract systematic artifacts observed in the amplitude values that are associated with variable slant-ranges and grazing angles. The procedure normalizes the raw amplitude values with the mean amplitude of all soundings in the survey collected at similar ranges and depths from the transducer. Second, the normalized amplitude values are gridded using the Generic Mapping Tools (GMT). Third, the amplitude grid is converted to ESRI ASCII grid format, loaded into ArcGIS and the two survey years are mosaiced together.

    Date: 11-Oct-2007 (process 2 of 2)
    First draft of metadata created by curator using FGDCMETA.AML ver. 1.35 08/02/2000 on ArcInfo data set /arcdata/sonar/tomales/tomalesampg

  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 advertised accuracy of the SWATHplus system in shallow waters is better than IHO S44 Special Order, but a total propagation error model has not been developed for the USGS system used in these surveys so the true error in both position and elevation is unknown.

  2. How accurate are the geographic locations?

    See Attribute_Accuracy_Report.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    Complete.

  5. How consistent are the relationships among the observations, including topology?

    Not applicable for raster data.

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: These data are not to be used for navigation.

  1. Who distributes the data set? (Distributor 1 of 1)

    United States Geological Survey (USGS)
    c/o Florence L. Wong
    Geologist, GIS Coordinator
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561
    USA

    (650) 329-5327 (voice)
    (650) 329-5190 (FAX)
    fwong@usgs.gov

  2. What's the catalog number I need to order this data set?

    USGS OFR 04-xxx

  3. What legal disclaimers am I supposed to read?

    Please recognize the U.S. Geological Survey (USGS) as the source of this information.

    Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data.

    The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 11-Oct-2007
Last Reviewed: Oct-2007
Metadata author:
United States Geological Survey (USGS)
c/o Florence L. Wong
Geologist, GIS Coordinator
USGS, MailStop 999, 345 Middlefield Road
Menlo Park, CA 94025-3561
USA

(650) 329-5327 (voice)
(650) 329-5190 (FAX)
fwong@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata ("CSDGM version 2") (FGDC-STD-001-1998)

Generated by mp version 2.8.11 on Wed Oct 24 13:22:16 2007