Coastal Relief Model of the Gulf of Farallones, Northern California

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Frequently-anticipated questions:


What does this data set describe?

Title:
Coastal Relief Model of the Gulf of Farallones, Northern California
Abstract:
The National Grids that integrate land and seafloor elevations are needed by planners using LIS/GIS software to manage the US coastal zone, which encompasses the coastal states out to the country's 200-mile offshore limit. Geophysical Data Center (NGDC) is addressing this need by assembling a gridded database that merges the US Geological Survey 3-arc-second DEMs with a vast compilation of hydrographic soundings collected by the National Ocean Service and various academic institutions. The principal component of the database is 3-arc-second elevation grids, of areas 1 degree in longitude by 1 degree in latitude, in which elevations are resolved to 1/10 of a meter. The database also includes grids containing the number of soundings enclosed by each cell in the offshore areas of the elevation grids, and images of both the elevation and sounding density grids. The latter are in common graphic formats that can be displayed by a range of UNIX-based and personal computer software.
  1. How should this data set be cited?

    Sweeney, Edward M. , 2004, Coastal Relief Model of the Gulf of Farallones, Northern California:.

    Online Links:

    This is part of the following larger work.

    Sweeney, E.M., Danforth, W.W., O'Brien, T. F. , Karl, H.A., and Schwab, W.C., 2004, The Gulf of the Farallones: Sidescan-Sonar Imagery: Open-File Report 2004-1082, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -124.027552
    East_Bounding_Coordinate: -121.971435
    North_Bounding_Coordinate: 39.005471
    South_Bounding_Coordinate: 36.995780

  3. What does it look like?

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

    Calendar_Date: 2001
    Currentness_Reference: publication date

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

    Geospatial_Data_Presentation_Form: remote-sensing image

  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 2687 x 2150 x 1, type Pixel

    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: 0.999600
      Longitude_of_Central_Meridian: -123.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 82.810425
      Ordinates (y-coordinates) are specified to the nearest 82.810425
      Planar coordinates are specified in meters

      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    The Coastal Relief Model TIFF image of the Gulf of Farallones is a shaded relief image. A shaded relief image is produced by applying an artificial light source to elevation (topographic or bathymetric) data. The azimuth, elevation, and vertical exaggeration are specified. The light source produces shadows within the imagery, as if the sun were shinning upon the region. Applying an artificial light source to elevation data, yields an image that is more easily interpreted by the end-user.


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?

    Edward M. Sweeney
    U.S. Geological Survey
    Research Assistant
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    (508) 548-8700 x2307 (voice)
    (508) 457-2310 (FAX)
    esweeney@usgs.gov


Why was the data set created?

The TIFF image generated from the Coastal Relief Model provides a basemap for Geographic Information System (GIS) database.


How was the data set created?

  1. From what previous works were the data drawn?

    NGDC Coastal Relief Model, U.S. Central Pacific Coast, vol. 7 (source 1 of 1)
    National Oceanic and Atmospheric Administration, 2001, Coastal Relief Model, Central Pacific Coast, Vol 7.

    Type_of_Source_Media: CD-ROM
    Source_Contribution:
    Vol 7 was used to create the TIFF image of the Gulf of the Farallones coastal relief

  2. How were the data generated, processed, and modified?

    Date: 2004 (process 1 of 1)
    The desired Coastal Relief Model data was extracted from volume 7 in ESRI ASCII format, and then converted to an ESRI grid. Using the ArcMap Spatial Analysis extension, a hillshade was then created from the ESRI grid file (Azimuth:30; Altitude:45; z-factor:1). After creating a desirable color scheme, the ESRI grid file and hillshade were combined using the ArcView extension grid-to-image converter tool (downloaded from www.esri.com) to create a TIFF image file and world file.

    Person who carried out this activity:

    Edward M. Sweeney
    U.S. Geological Survey
    Research Assistant
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    (508) 548-8700 x2307 (voice)
    (508) 457-2310 (FAX)
    esweeney@usgs.gov

  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?

    Soundings for each volume of the Coastal Relief model series are compiled from hydrographic surveys conducted by the National Ocean Service (NOS) and from various academic institutions. The surveys were carried out using a variety of sounding methods including SeaBeam 16-beam, 12-kHz swath mapping system (6000- >3000m operating water depths), General Instruments 17-beam, 36-kHz Hydrochart II swath mapping system (5-150m operating water depths), single-beam echosounder (e.g., 3.5 kHz narrow 2 degree beam), and lead-line sounding method. These latter surveys date as far back as the late 1800's.

    A wide range of navigation methods are also associated with the surveys. Visual navigation is based on three-point sextant fixes, theodolite intersections, and celestial fixes. Electronic navigation involves short to long range positioning systems that run the gamut from Loran-C (0.25 - 5 nm accuracy) to differential GPS ( 1 m accuracy).

    Despite the varying sounding and navigation techniques upon which they are based, all of the NOS soundings used in constructing the Coastal Relief Model meet rigorous standards for accuracy. The same standards are employed by the International Hydrographic Office and have remained relatively consistent since the 1800's. The vertical accuracy of the soundings

    The horizontal accuracy of the soundings is generally 30 m, but it can vary from as fine as 15 m in ports and estuaries to as coarse as 75 m in the offshore areas. Differential GPS has improved this level of accuracy considerably for the most recent survey data.

  2. How accurate are the geographic locations?

    The horizontal accuracy of the soundings is generally 30 m, but it can vary from as fine as 15 m in ports and estuaries to as coarse as 75 m in the offshore areas.

  3. How accurate are the heights or depths?

    The vertical accuracy of the soundings is 0.3 m in 0 - 20 m of water, 1.0 m in 20 - 100 m of water, and 1% of the water depth in 100 m of water.

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

    These data are complete (see: <http://www.ngdc.noaa.gov/mgg/coastal/model.html>)

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

    Land elevations within the gridded dataset come from the United States Geological Survey/ National Image Mapping Agency (USGS/NIMA) 1:250,000 or 1 degree DEMs of the states. A description of the USGS/NIMA DEMs and how they were derived can be accessed on the World Wide Web at <http://edcwww.cr.usgs.gov/glis/hyper/guide/1_dgr_dem>. Our focus, however, is on the bathymetric soundings that are used in constructing the offshore regions of the grids.

    Soundings for each volume of the Coastal Relief model series are compiled from hydrographic surveys conducted by the National Ocean Service (NOS) and from various academic institutions. The surveys were carried out using a variety of sounding methods including SeaBeam 16-beam, 12-kHz swath mapping system (6000- >3000m operating water depths), General Instruments 17-beam, 36-kHz Hydrochart II swath mapping system (5-150m operating water depths), single-beam echosounder (e.g., 3.5 kHz narrow 2 degree beam), and lead-line sounding method. These latter surveys date as far back as the late 1800's.

    A wide range of navigation methods are also associated with the surveys. Visual navigation is based on three-point sextant fixes, theodolite intersections, and celestial fixes. Electronic navigation involves short to long range positioning systems that run the gamut from Loran-C (0.25 - 5 nm accuracy) to differential GPS ( 1 m accuracy).

    Despite the varying sounding and navigation techniques upon which they are based, all of the NOS soundings used in constructing the Coastal Relief Model meet rigorous standards for accuracy. The same standards are employed by the International Hydrographic Office and have remained relatively consistent since the 1800's. The vertical accuracy of the soundings is 0.3 m in 0 - 20 m of water, 1.0 m in 20 - 100 m of water, and 1% of the water depth in 100 m of water. The horizontal accuracy of the soundings is within a radius of 1.5 mm of the sounding location at the scale at which the soundings are recorded. NOS surveys are plotted at map scales that range from 1/10,000 for harbors and channels to 1/50,000 for open ocean surveys, with 1/20,000 being the most commonly used scale. The horizontal accuracy of the soundings is generally 30 m, but it can vary from as fine as 15 m in ports and estuaries to as coarse as 75 m in the offshore areas. Differential GPS has improved this level of accuracy considerably for the most recent survey data.

    While the NOS soundings collected since 1965 have been recorded digitally, those collected prior to this time were recorded manually and then used to make hand-drawn bathymetric maps. Approximately 1,550 of these hand-drawn bathymetric maps have been digitized and assimilated into the NOS Hydrographic Database and, subsequently, were used in constructing the many volumes of the gridded dataset.


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:
Public domain data from the U.S. government is freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of this dataset.

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

    Nancy Soderberg
    U.S. Geological Survey
    Data Librarian
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    (508) 548-8700 x2275 (voice)
    (580)457-2313 (FAX)
    nsoderberg@usgs.gov

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

    Farallones_CRM.tif

  3. What legal disclaimers am I supposed to read?

    Although this data set and its lineage have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data or its related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related items. Users must assume responsibility for the proper use of these data. The data should not be used at resolutions for which they are not intended. The data have not been reviewed for conformity with U.S. Geological Survey editorial standards, or the North American Strigraphic code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government.

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 19-Apr-2004
Metadata author:
Edward M. Sweeney
U.S. Geological Survey
Research Assistant
384 Woods Hole Rd.
Woods Hole, MA 02543
USA

(508) 548-8700 x2307 (voice)
(508) 457-2310 (FAX)
esweeney@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)


Generated by mp version 2.8.7 on Mon Jul 19 11:52:58 2004