Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2008, Line, grid, and vector data, and maps for the airborne geophysical survey data of the Styx River Survey, parts of the Lime Hills and Tyonek quadrangles, southcentral Alaska: Geophysical Report GPR 2008-3, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 25
Ordinates (y-coordinates) are specified to the nearest 25
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.
Funding was provided by the Alaska State Legislature as part of the DGGS Airborne Geophysical/Geological Mineral Inventory (AGGMI) program and by a contribution by Anglo America Exploration (USA) Inc. The contribution from Anglo American allowed us to acquire data for about 180 square miles of the 715 sq mile survey, all included in this DVD.
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The survey was part of the Alaska Airborne Geophysical/Geological Mineral Inventory project funded by the Alaska State Legislature and managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The project seeks to catalyze private-sector mineral development investment. The project delineates mineral zones on Alaska state lands that: 1) have major economic value; 2) can be developed in the short term to provide high quality jobs for Alaska; and 3) will provide economic diversification to help offset the loss of Prudhoe Bay oil revenue.
Akima, H., 1970, A new method of interpolation and smooth curve fitting based on local procedures: Journal of the Association of Computing Machinery v. 7, no. 4.
Data sources used in this process:
Data sources used in this process:
Geophysical data were acquired during an airborne survey. The magnetometer used had a sensitivity of 0.01 nT. Resistivity sensitivity varies among the different frequencies from 0.06 ppm to 0.30 ppm. Survey contracts specified the conditions and specifications under which these data were collected. Altimeter, heading, lag, and frequent EM calibrations were done. More information will be available in the project report to be published in the future.
The helicopter position was derived every 0.5 seconds using post-flight differential positioning 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.
The accuracy of the elevation calculation used for the digital elevation model is directly dependent on the accuracy of the two input parameters, ALTR and HMSL. The ALTR value may be erroneous in areas of heavy tree cover, where the altimeter reflects the distance to the tree canopy rather than the ground. The HMSL (or GPS-Z) value is primarily dependent on the number of available satellites. Although post-processing of GPS data will yield X and Y accuracies in the order of 5 meters, the accuracy of the Z value is usually much less, sometimes in the ±20 meter range.
This dataset includes files that contain processed aeromagnetic measurements, electromagnetic measurements, altimetry measurements, and locational data for the survey area. Areas with no data for a given channel are flagged with the dummy variable (*). These may be representing 1) spikes and dropouts in the magnetic reading, due to various reasons; 2) resistivity and depth values that are not calculated because flying height was too high to produce meaningful calculations, 3) sampling differences, e.g., most sampling was 10 samples per second, but the diurnal_filt was 1 sample per second, and 4) lag shift at the end of a line. The Res900 has more dummy variables than the Res7200, which has more dummy variables than the Res56K.
Data for this survey were collected by a single subcontractor (Fugro Airborne Surveys) who was responsible for collecting and processing the data. At the request of DGGS, the data were acquired in two different time periods, October-November 2007 and March-April 2008. A late fall contribution of funds from Anglo American Exploration (USA) Inc. allowed us to acquire more data for the public, but logistics then required a delay for part of the survey. The data from both parts of this survey were collected with the same instruments (magnetometers, electromagnetic bird and sensors, altimeters, and navigational system). All channels of the electromagnetic system functioned with very little noise through both parts of the survey. See Process_steps for information on the IGRF calculations.
Are there legal restrictions on access or use of the data?
- 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).
- 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).
Geophysical Report 2008-3
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.
Maps from current publication are available on paper or Mylar. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (firstname.lastname@example.org), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard.
|Data format:||digital raster data, digital tabular data, digital vector data (version n/a)|
|Media you can order:||
Digital files on DVD are available for $10 plus shipping and are available for no charge when downloaded.
Order by phone (907-451-5020), e-mail (email@example.com), or fax (907-451-5050). Payment accepted: cash, check, money order, VISA, or MasterCard. The geophysics page of the DGGS web site (<http://www.dggs.alaska.gov/geophysics/>) has geophysical order forms for this project and others.
Digital downloads: Less than 30 minutes for most files. Free FTP access is available upon request for files not available on the web. Offline DVDs: 1-2 weeks unless special arrangements are made and an express fee is paid.
Custom views or processing may be requested. Please contact the geophysicist to discuss custom processing availability, fees, and turnaround time.
Software with ability to use, import, or convert Geosoft binary float .grd, Geosoft ASCII .xyz, Er Mapper .ers, Autocad .dxf, Adobe Acrobat files and text files. A free downloadable interface (currently called Oasis Montaj Viewer) is available at the Geosoft website (<http://www.geosoft.com>) and will open Geosoft files and Autocad dxf files. For magnetic files, the default color scheme (colour.tbl) is appropriate for viewing. In order to view the resistivity files in the standard color scheme, change the color table to reflect resistivity colors (resis.tbl). Freeware software 'printfile' (<http://www.lerup.com/printfile/>) prints HPGL/2 files easily on compatible printers. The HPGL/2 files have brighter colors and sharper topography than the PDF maps and should be used for printing when possible. The PDF format maps are the only maps digitally viewable in this publication.