Marine magnetic data from Point Sur to Piedras Blancas, central California, 2011

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Frequently anticipated questions:

What does this data set describe?

Marine magnetic data from Point Sur to Piedras Blancas, central California, 2011
This dataset includes marine magnetic data collected by the U.S. Geological Survey (USGS) in 2011 during field activity B-05-11-CC between Point Sur and Piedras Blancas, central California.
Additional information about the field activity from which these data were derived is available online at: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  1. How might this data set be cited?
    Watt, Janet T., Hartwell, Stephen R., and Johnson, Samuel Y., 2018, Marine magnetic data from Point Sur to Piedras Blancas, central California, 2011: data release DOI:10.5066/F7FB51F7, 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: -121.912539
    East_Bounding_Coordinate: -121.316979
    North_Bounding_Coordinate: 36.265058
    South_Bounding_Coordinate: 35.649101
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 12-Sep-2011
    Ending_Date: 26-Sep-2011
    ground condition at the time the data were collected
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Point (363903)
    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 0.00001. Longitudes are given to the nearest 0.00001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North American Datum of 1983.
      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.
      Depth_Datum_Name: Local surface
      Depth_Resolution: 0.1
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Attribute values
  7. How does the data set describe geographic features?
    Points representing magnetic anomaly level (Source: USGS)
    Survey line identifier (Source: USGS) Each line contained in the survey has a unique identifier
    Date of data point collection in M/DD/YY format (Source: USGS)
    Range of values
    Time of data point collection in HH:MM:SS format (Source: USGS)
    Range of values
    Longitude of data point in decimal degrees (Source: USGS)
    Range of values
    Latitude of data point in decimal degrees (Source: USGS)
    Range of values
    X coordinate of data point in meters (Source: USGS)
    Range of values
    Y coordinate of data point in meters (Source: USGS)
    Range of values
    Raw, unprocessed, magnetic level at data point (Source: USGS)
    Range of values
    Magnetic level correction applied (Source: USGS)
    Range of values
    Magnetic level with International Geomagnetic Reference Field (IGRF) correction applied (Source: USGS)
    Range of values
    Value of International Geomagnetic Reference Field at the Fresno Base at the time data point was collected (Source: USGS)
    Range of values
    Calculated Total Field (Residual) Anomaly (see Process Step 6) (Source: USGS)
    Range of values
    Magnetic level Final-magnetic level with directional correction applied (Source: USGS)
    Range of values

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Janet T. Watt
    • Stephen R. Hartwell
    • Samuel Y. Johnson
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Janet T. Watt
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    (831) 460-7565 (voice)
    (831) 427-4748 (FAX)

Why was the data set created?

These data and information are intended for science researchers, students from elementary through college, policy makers, and general public.

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: 27-Jun-2013 (process 1 of 2)
    Magnetic data were postprocessed following the methodology: 1)Initial Processing in MagMap2000 -Download base files from INTERMAGNET observatory ( -Despike base files and visually inspect for dropouts -Apply bias to DIURNAL (base) readings for GMT to local PDT + longitude diff. from base to survey = 7hrs + 0.22hrs =-24,408sec **NOTE: 0.0666667hr/deg longitude correction -Import .survey files, despike
    2)Import to Oasis -Remove periodic sparker spike from raw G882 and G882_diurnal channel using a non-linear filter GX = nlfilt (ex. filter width = 3 data points, filter tolerance = 0.3 nt)
    3)Calculated IGRF for G882 data
    4)Back calculated Base Magnetometer measurements G882filt-DIURNAL_filt = Fresno_base
    5)Calculated IGRF value at base station FRN = 48909.6nT
    6)Calculated Total Field (Residual) Anomaly using the following equation: A(x) = [F(x,t) - I(x)] - [FB(t) - IB]
    where: A(x)is total field anomaly at position x F(x,t) is the G882 reading at time t and position x I(x) is IGRF/DGRF at the G882 FB(t) is the base station reading at time t IB is the IGRF/DGRF at the base station
    7)Performed tie line leveling 8) Manually edited a subset of lines (+6 nT) 9) Applied a decorrugation filter "L" lines only (500m line spacing, line azimuth=30 degrees) Following methodology at Geosoft -
    FILTER PARAMETERS for "L" lines Butterworth filter: cutoff wavelength = 2000 (4 x line spacing) filter order = 8 (suggested) high-pass
    Directional Cosine filter: centre direction = 30 (shiptrack azimuth) degree of cosine function = 0.5 (suggested)
    Date: 19-Oct-2020 (process 2 of 2)
    Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
  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?
    Identified as best available version.
  2. How accurate are the geographic locations?
    10-25 meters, depending on ship speed
  3. How accurate are the heights or depths?
    not applicable for these data
  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?
    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.
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.
  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)
  2. What's the catalog number I need to order this data set? Downloadable magnetic field data These data are available in shapefile format (PointSurToPiedrasBlancas_magnetics.shp and associated files) contained in a single zip file (, which also include 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?
  5. What hardware or software do I need in order to use the data set?
    This shapefile can be viewed with Esri or other GIS software.

Who wrote the metadata?

Last modified: 19-Oct-2020
Metadata author:
Janet T. Watt
U.S. Geological Survey, Pacific Coastal and Marine Science Center
2885 Mission Street
Santa Cruz, CA

831-460-7565 (voice)
831-427-4748 (FAX)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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