Linedata and gridded data for the aeromagnetic survey of the Holitna basin area, western Alaska; Parts of the Lime Hills and Sleetmute quadrangles

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Frequently-anticipated questions:

What does this data set describe?

Title:
Linedata and gridded data for the aeromagnetic survey of the Holitna basin area, western Alaska; Parts of the Lime Hills and Sleetmute quadrangles
Abstract:
This DVD-ROM publication, GPR 2008-4, contains linedata, gridded data, vector data, and browse graphics produced from a fixed-wing aeromagnetic survey conducted in 1997 of the Holitna Basin area, western Alaska. Aeromagnetic data were acquired for about 3234 sq miles for the Alaska Division of Geological & Geophysical Surveys (DGGS) during this fixed-wing survey.
Supplemental_Information:
The data were acquired, processed, and interpreted under contract between the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), and On-line Exploration Services, Inc. Aeromagnetic data for the area were acquired and processed by SIAL Geosciences, Inc. in 1997-1998. Some of the other publications for the CIP project are listed in the cross-references. More Holitna publications can be found by searching the DGGS publications for 'Holitna' at the DGGS Web site <http://www.dggs.alaska.gov/pubs/advanced-search>. Data provided in GPR 2008-4 include (1) processed and raw linedata ASCII files, (2) gridded files described below, (3) vector files of magnetic contours, flight path, and locational aids, and (4) a browse graphic file in PDF format. Gridded magnetic data include IGRF-removed total magnetic field, horizontal and vertical gradients (first derivatives), Euler deconvolution depth-to-basement models, and analytic signals. The Euler grids herein were produced by Sial Geosciences, Inc. and were included as page-sized color figures in the contractor's project report 'DGGS Public Data File 98-29', listed both as a source (SIAL and On-line, 1998) and as a cross reference in this metadata. Data are described in more detail in 'GPR2008-4Readme.pdf' and the browse-graphic file of this publication, and in the contractor's project report, referred to hereafter as 'SIAL and On-Line (1998)'.
  1. How should this data set be cited?

    Burns, L.E., SIAL Geosciences, Inc., and On-line Exploration Services, Inc., 2008, Linedata and gridded data for the aeromagnetic survey of the Holitna basin area, western Alaska; Parts of the Lime Hills and Sleetmute quadrangles: Geophysical Report GPR 2008-4, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 CD

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -157.47
    East_Bounding_Coordinate: -155.16
    North_Bounding_Coordinate: 62.06
    South_Bounding_Coordinate: 60.95

  3. What does it look like?

    GPR2008-4BrowseGraphic.pdf (PDF)
    The browse graphic file, 'GPR2008-4BrowseGraphic.pdf' contains images of all the geophysical grids contained in this publication and a shaded-relief image of the total magnetic field. Included figures are Figure 1a: Total field magnetic map of the Holitna survey map area; Figure 1b: Total field magnetic map of all the Holitna survey data; Figure 2a: Horizontal gradient (dx) of the Holitna magnetic grid; Figure 2b: Horizontal gradient (dy) of the Holitna magnetic grid; Figure 2c: First vertical derivative (dz) of the Holitna magnetic grid; Figure 3: Color shadow map of the total field magnetic data; Figure 4a: Depth interpretation using Euler deconvolution with dike model, log-linear color method; Figure 4b: Depth interpretation using Euler deconvolution with step model, log-linear color method; Figure 4c: Depth to basement model using Euler deconvolution with dike model, log-linear color method; Figure 4d: Depth to basement model using Euler deconvolution with dike model, normal distribution color method; Figure 4e: Depth to basement model using Euler deconvolution with dike model, histogram equalization color method; Figure 5a: Analytic signal of the total magnetic field computed using Fast Fourier Transforms (FFT) for the z-derivative; log-linear color method; Figure 5b: Analytic signal of the total magnetic field computed using Fast Fourier Transforms (FFT) for the z-derivative; normal distribution color method; Figure 5c: Analytic signal of the total magnetic field computed using Fast Fourier Transforms (FFT) for the z-derivative; histogram equalization color method; Figure 5c: Analytic signal of the total magnetic field computed using Fast Fourier Transforms (FFT) for the z-derivative; histogram equalization color method; and Figure 5d: Analytic signal of the total magnetic field computed using convolution for the z-derivative; histogram equalization color method.

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

    Beginning_Date: Jul-1997
    Ending_Date: Jul-2008
    Currentness_Reference: publication date

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

    Geospatial_Data_Presentation_Form: raster digital data, tabular digital data, vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 4
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -159
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000
      False_Northing: 0

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 200
      Ordinates (y-coordinates) are specified to the nearest 200
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.978698.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    Entities (file names) as well as the attributes of the linedata files are listed in the 'GPR2008-4Readme.pdf' file included on this CD-ROM.
    Entity_and_Attribute_Detail_Citation:
    L.E. Burns, Division of Geological & Geophysical Surveys and SIAL Geosciences, Inc.

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?

    The Alaska State Legislature provided funding for the geophysical data and project management through a Capital Improvement Project requested by Calista Native Corporation.

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

Why was the data set created?

The survey was part of a Capital Improvement Project funded by the Alaska State Legislature at the request of Calista Native Corporation. The purpose of the Capital Improvement Project was to provide data to assist in evaluation of the hydrocarbon potential of the Holitna basin area. The survey was managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS).

How was the data set created?

  1. From what previous works were the data drawn?

    SIAL, 1998 (source 1 of 2)
    SIAL Geosciences, Inc., Unpublished material, Geophysical data for the Holitna basin area, western Alaska.

    Type_of_Source_Media: CD-ROM
    Source_Contribution:
    The linedata files, the grid files Mag_MapArea.grd, EulDepDk.grd, EulDepSt.grd, and Depth2Basement_MapArea.grd, and the vector files (.PLT and .DXF formats) were renamed and copied onto this publication. Column names for final linedata were taken from this CD-ROM. The final linedata file was used as the basis for the other grids included in this publication.

    SIAL and On-line, 1998 (source 2 of 2)
    SIAL Geosciences, Inc., and On-line Exploration, Inc., 1998, Project report of the aeromagnetic survey for the Holitna Basin area, western Alaska: Public Data File PDF 98-29, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 82 p., 2 interpretative sheets, scale 1:125,000
    Type_of_Source_Media: paper
    Source_Contribution:
    Much of the information in this metadata file, particularly the process steps, was taken from this report. Columns names for the raw linedata were taken from this report.

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

    Date: 1997 (process 1 of 4)
    The geophysical data were acquired with a RMS GR-33/HDS60 data acquisition system, and a Geometrics G822A cesium magnetometer installed in a stinger configuration in a Piper Navajo 310 airplane. In addition, the survey recorded data from a radar altimeter (King KRA-10), GPS navigation system, and video camera. Flights were performed at a mean terrain clearance of 300 ft along N35W survey flight lines with a spacing of one-half mile. Tie lines were flown perpendicular to the flight lines at intervals of approximately three miles. Two Trimble-4000 SE Differential Post-processing Global Positioning Systems were used for navigation and flight path recovery. The GPS receivers locked on to at least 4 satellites. Post-processing position accuracy was better than 5 meters. The data were acquired during September 8th and October 7th, 1997. The barometric altimeter was calibrated with the radar altimeter pre- and post- each flight. The 'drift' for the barometric altimeter was determined by flying over an airstrip of known elevation at several altitudes. This drift and the GPS altitude were used to correct the barometric altitude of each flight.

    Data sources used in this process:

    • SIAL and On-line, 1998

    Date: 1998 (process 2 of 4)
    The airborne magnetic data were acquired with a sampling interval of 0.1 seconds, and were corrected for measured system lag. Data from airborne and base magnetometers were inspected in order to remove discrete spikes and cultural noise. A 30 second low-pass filter was applied to remove small amplitude noise. Diurnal corrections were applied to the airborne magnetic data and the IGRF was removed. Final leveling was done by intersection analysis. A constant was added back to this residual data. The total field magnetic data were then interpolated onto a 200-m grid using GEOSOFT minimum curvature gridding to produce the grid 'Mag_MapArea.grd' in Geosoft short format, included in this publication.

    Data sources used in this process:

    • SIAL and On-line, 1998

    Date: 1998 (process 3 of 4)
    Euler deconvolution was used to produce the depth-to-basement grids, shown in the browse graphic file as Figures 4a-e and in the SIAL and On-line (1998) as Figures 40, 41, and 42. Dike and step source geometries were used. The dike model gave a maximum basement depth of 6490 meters and the step model give a maximum basement depth of 5350 meters. Blank regions on figures 4a and 4b are areas where no Euler solutions were found. Because the dike model was more compatible with the spectral analysis results discussed in SIAL and On-line (1998), SIAL filled in the indeterminate areas in the dike model grid and considered it as the best depth-to-basement model they produced. In order to fill in the indeterminate areas, the data were regridded with a longer radius by SIAL. The Geosoft short data format grids, EulDepDk, EulDepSt, and Depth2Basement were produced as a 200-m grid.

    Data sources used in this process:

    • SIAL and On-line, 1998

    Date: 2008 (process 4 of 4)
    After much investigation, all appropriate files on the CD-ROM provided by SIAL were selected for this publication. The final linedata were imported into Geosoft's Oasis Montaj and were used as the basis for the processes described here. Resulting grids mentioned here were all produced in Geosoft float format. The total field magnetic data were interpolated onto a 200-m grid using minimum curvature gridding to produce the grid 'mag.grd'. The grids dx, dy, and dz were produced using the Source Parameter Imaging (SPI) function, a trademark of Geoterrex. Two analytic signal grids were produced by applying filters to the magnetic grid. One method applied a Fast Fourier transform (FFT) to acquire the vertical derivative, and the other used convolution to acquire the vertical derivative. Both are included. Images of all of the gridded data on this CD-ROM are included in the browse-graphic file, GPR2008-4BrowseGraphic.pdf. A shaded-relief (color shadow) image of the magnetic grid was also produced and included. The figures were produced in Oasis Montaj and printed to Adobe Acrobat files.

    Data sources used in this process:

    • SIAL, 1998

  3. What similar or related data should the user be aware of?

    Alaska Division of Geological & Geophysical Surveys Staff, On-line Exploration Services, Inc., and SIAL Geosciences, Inc., 1998, Total field magnetics of the Holitna Basin area, western Alaska: Report of Investigation RI 98-14, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details:
    color, 2 sheets, scale 1:125,000, data contours included, no topography
    Alaska Division of Geological & Geophysical Surveys, On-line Exploration Services, Inc., and SIAL Geosciences, Inc., 1998, Total field magnetics and field line paths of the Holitna Basin area, western Alaska: Public Data File PDF 98-27, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: black and white, 4 sheets, scale 125,000, topography included
    SIAL Geosciences, Inc., and On-line Exploration Services, Inc., 1998, Project report of the aeromagnetic survey for the Holitna Basin area, western Alaska: Public Data File PDF 98-29, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 82 p., 2 interpretative sheets, scale 1:125,000
    LePain, D.L., Blodgett, R.B., Clough, J.G., and Ryherd, T.J., 2000, Generalized stratigraphy and petroleum potential of the Holitna region, southwest Alaska: Preliminary Interpretive Report PIR 2000-1, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 34 p., 1 sheet, scale 1:250,000
    LePain, D.L., Blodgett, R.B., and Clough, J.G., 2003, Sedimentology and hydrocarbon source rock potential of Miocene-Oligocene strata, McGrath Quadrangle: An outcrop analog for the Holitna Basin: Preliminary Interpretive Report PIR 2002-5, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 75 p.
    Edcon, Inc., 2001, Edcon land gravity survey, Holitna Basin, southwest Alaska: Geophysical Report GPR 2001-1, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    • none

    Other_Citation_Details: 1 disk

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

  1. How well have the observations been checked?

    Survey contracts specified the conditions and specifications under which these data were collected. Pre-survey Figure of Merit (FOM), Bourget calibrations, and lag tests were conducted between Sept. 1st and Sept. 7th, 1997. After spikes in the magnetic data were detected on September 22nd, a new magnetic sensor was installed and a new FOM was performed. Field barometric corrections were based on pre- and post-flight measurements made over the airstrip. Further discussion of calibrations and test results are given in the contractor's project report (SIAL and Online, 1998).

  2. How accurate are the geographic locations?

    The position of the Piper Navajo 310 airplane position was derived every 1.0 second using post-flight processing to a relative accuracy of better than 5 m. Positional accuracy of the presented data is better than 10 m with respect to the UTM grid. Further inaccuracies may be introduced by the interpolation and gridding process.

  3. How accurate are the heights or depths?

    The survey was flown draped over topography with a constant terrain clearance specification of 300 feet. A King KRA-10 radar altimeter with a resolution of 4 mV/foot, an accuracy of 1 percent over flat terrain, and better than 10 feet sensitivity was used. A Rosemount 1241 barometric altimeter was used with a resolution of 1 mV/foot, an accuracy of +/- 7 feet, and electronic drift less than 10 feet/hour. Further discussion of altimetry data are given in Sial and On-line (1998).

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

    Data are complete. No dummy values were used in the linedata.

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

    Data for this survey were collected by a single subcontractor, SIAL Geoscience, Inc. who was responsible for collecting and processing the data. Most vector files are provided in both Autocad DXF and Geosoft PLT format in this publication; while containing the same information, the DXF files are better most of the time for large plots and the PLT files are generally better for smaller figures. No topological relationships are included.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints:
This report, map and/or dataset are available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way the user is obligated to describe the types of modifications the user has made. User specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS).

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

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
    Natural Resource Technician
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    907-451-5020 (voice)
    907-451-5050 (FAX)
    dggspubs@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our Web site (<http://www.dggs.alaska.gov>) for the latest information on available data. Please contact us using the e-mail address above whenever possible.
  2. What's the catalog number I need to order this data set?

    Geophysical Report 2008-4

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester or anyone else exceed the fee paid for the electronic service or product.

  4. How can I download or order the data?

  5. Is there some other way to get the data?

    Custom views or processing may be requested. Please contact Laurel Burns by phone (907-451-5021), e-mail (laurel.burns@alaska.gov), or fax (907-451-5050) to discuss custom processing availability, fees, and turnaround time.

  6. What hardware or software do I need in order to use the data set?

    Software with ability to use, import, or convert Geosoft .grd files, Geosoft .xyz (ASCII) files, Autocad .dxf files, Adobe Acrobat files, and text files. Free downloadable interfaces for accessing the gridded and dxf files are available at the Geosoft Web site (<http://www.geosoft.com>; Oasis Montaj viewer), and the ER Mapper Web site (<http://www.ermapper.com>). Maps are accessed digitally using Adobe Acrobat. Maps are printed from the Adobe Acrobat files.

Who wrote the metadata?

Dates:
Last modified: 23-Jul-2008
Last Reviewed: 23-Jul-2008
To be reviewed: 23-Jul-2011
Metadata author:
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
Geophysicist
3354 College Road
Fairbanks, AK 99709-3707
USA

907-451-5021 (voice)
907-451-5050 (FAX)
dggspubs@alaska.gov

Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays.
Contact_Instructions:
Please contact us through the e-mail address above whenever possible.
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

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