Burns, L.E.
U.S. Bureau of Land Management
Fugro Airborne Surveys Corp.
Stevens Exploration Management Corp.
2008
Line, grid, and vector data, plot files, and descriptive project report for the airborne geophysical survey of part of the western Fortymile mining district, east-central Alaska
raster digital data, tabular digital data, vector digital data, and atlas
Geophysical Report
GPR 2008-1
Fairbanks, AK, USA
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
1 DVD
http://www.dggs.alaska.gov/pubs/geophysics
This digital publication, GPR 2008-1, contains geophysical data and a digital elevation model that were produced from airborne geophysical surveys conducted in 2007 for part of the western Fortymile mining district, east-central Alaska. Aeromagnetic and electromagnetic data were acquired for 250 sq miles during the helicopter-based survey.
Data provided in GPR 2008-1 include processed (1) linedata ASCII database, (2) gridded files of magnetic data, a calculated vertical magnetic gradient (first vertical derivative), apparent resistivity data, and a digital elevation model, (3) vector files of data contours and flight lines, and (4) the Contractor's descriptive project report. Data are described in more detail in the "GPR2008-1Readme.pdf" and "linedata/GPR2008-1-Linedata.txt" files included on the DVD.
The survey was funded by the U.S. Department of Interior, Bureau of Land Management in support of the State of Alaska's Airborne Geophysical/Geological Mineral Inventory project. The data were produced to provide information for mineral resource evaluation and land management decisions.
The maps were compiled and drawn under contract between the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), and Stevens Exploration Management Corp. Airborne geophysical data for the area were acquired and processed by Fugro Airborne Surveys in 2007. This publication also contains HPGL2 and Adobe Acrobat files for all maps produced to date for this project. All maps included on this publication are full color. Authors for the individual maps are the same as for this publication. The maps on GPR 2008-1 include:
GPR 2008-1-1a - Total magnetic field of part of the western Fortymile mining district, east-central Alaska; topography included; scale 1:63,360, 1 sheet.
GPR 2008-1-1b - Total magnetic field of part of the western Fortymile mining district, east-central Alaska; magnetic data contours included; scale 1:63,360, 1 sheet.
GPR 2008-1-1c - First vertical derivative of the total magnetic field of part of the western Fortymile mining district, east-central Alaska; topography included; scale 1:63,360, 1 sheet.
GPR 2008-1-2a - 56,000 Hz coplanar apparent resistivity of part of the western Fortymile mining district, east-central Alaska; topography included; scale 1:63,360, 1 sheet.
GPR 2008-1-2b - 56,000 Hz coplanar apparent resistivity of part of the western Fortymile mining district, east-central Alaska; 56,000 Hz resistivity data contours included; scale 1:63,360, 1 sheet.
GPR 2008-1-3a - 7200 Hz coplanar apparent resistivity of part of the western Fortymile mining district, east-central Alaska; topography included; scale 1:63,360, 1 sheet.
GPR 2008-1-3b - 7200 Hz coplanar apparent resistivity of part of the western Fortymile mining district, east-central Alaska; 7200 Hz resistivity data contours included; scale 1:63,360, 1 sheet.
GPR 2008-1-4a - 900 Hz coplanar apparent resistivity of part of the western Fortymile mining district, east-central Alaska; topography included; scale 1:63,360, 1 sheet.
GPR 2008-1-4b - 900 Hz coplanar apparent resistivity of part of the western Fortymile mining district, east-central Alaska; 900 Hz resistivity data contours included; scale 1:63,360, 1 sheet.
An index map showing the locations of the 1:63,360-scale map sheets are included on this publication. Bounding coordinates for the sheets are given immediately below. The bounding coordinates of the gridded data are given in the "Bounding_Coordinates" section below.
1:63,360-scale maps, sheet 1 West, -143.42
1:63,360-scale maps, sheet 1 East, -142.58
1:63,360-scale maps, sheet 1 North, 64.38
1:63,360-scale maps, sheet 1 South, 63.92
200709
200712
publication date
None
-143.39
-142.61
64.36
63.95
ISO 19115 Topic Category
geoscientificInformation
none
Aeromagnetic Data
Aeromagnetic Map
Airborne Geophysical Survey
Apparent Resistivity Data
Apparent Resistivity Map
Apparent Resistivity Contours
Digital Elevation Model
DIGHEM V EM System
Electromagnetic Data
First Vertical Derivative
Geophysics
HEM Survey
Magnetic Contours
none
Alaska, State of
Eagle Quadrangle
Fortymile Mining District
Tanacross Quadrangle
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).
The U.S. Bureau of Land Management provided funding for the 2007 geophysical data and project management.
Microsoft Windows XP Professional Version 2002 Service Pack 2; Geosoft Oasis Montaj Version 6.3; Autocad Version 2000; ER Mapper 6.3, HP Designjet 5000 or 5500 plotters, HP plotters that can read Postscript 3, and Adobe Acrobat PDF writer Version 7.0
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.
No topological relationships are included.
This dataset includes files that contain processed aeromagnetic measurements, electromagnetic measurements, altimetry measurements, and locational data for the survey area.
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.
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
None
paper
1970
1970
Akima, 1970
Fugro Airborne Surveys used a modification of this method while making grids.
The Alaskan section grid, taken from the DGGS network, was modified by DGGS to align some of the section lines with the section lines on the U.S. Geological Survey 1:63,360-scale topographic maps of the area. Modification involved moving about an eighth or less of the east-west and north-south lines, particularly in the western portions of the quadrangle sheets. Movement was generally on the order of a tenth of a mile. The section grid file contained here may not be identical to the section grid available through Alaska Department of Natural Resources, Land Record Information Section (LRIS).
2007
The airborne geophysical data were acquired with a DIGHEM(V) Electromagnetic (EM) system and a Fugro D1344 cesium magnetometer with a Scintrex CS3 cesium censor. The EM and magnetic sensors were flown at a height of 100 feet. In addition, the survey recorded data from a radar altimeter, GPS navigation system, 50/60 Hz monitors, and video camera. Flights were performed with an AS350B-3 Squirrel helicopter at a mean terrain clearance of 200 feet along N-S survey flight lines with one-quarter mile line spacing. Tie lines were flown perpendicular to the flight lines at intervals of approximately 3 miles. A Novatel OEM4 Global Positioning System was used for navigation and flight path recovery. The helicopter position was derived every 0.5 seconds using post-flight differential positioning to a relative accuracy of better than 5 m. Flight path positions were projected onto the Clarke 1866 (UTM zone 7) spheroid, 1927 North American datum using a central meridian (CM) of 141 degrees, a north constant of 0 and an east constant of 500,000.
2007
The total magnetic field data were acquired with a sampling interval of 0.1 seconds, and were (1) corrected for measured system lag, (2) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data (saved as tfmag in Fortymile-Linedata.xyz), (3) adjusted for regional variations (or IGRF gradient, 2005, updated to September 2007) using altimeter adjusted IGRF, (4) leveled to the tie line data (saved as magigrf in Fortymile-Linedata.xyz), and (5) interpolated onto a regular 80-m grid using a modified Akima (1970) technique.
The total magnetic field data were subjected to a processing algorithm that enhances the response of magnetic bodies in the upper 500 m and attenuates the response of deeper bodies. The resulting vertical gradient grid (Fortymile-cvg) provides better definition and resolution of near-surface magnetic units. It also identifies weak magnetic features that may not be evident on the total field data.
All magnetic grids were then resampled from the 80-m cell size down to a 25-m cell size using a modified Akima (1970) technique to produce the maps and final grids contained on this publication.
Akima, 1970
2007
The DIGHEM V EM system measured inphase and quadrature components at five frequencies. Two vertical coaxial-coil pairs operated at 1125 (1000) and 5454 (5500) Hz while three horizontal coplanar-coil pairs operated at 875 (900), 7153 (7200), and 55,400 (56,000) Hz. The EM data were sampled at 0.1 second intervals. The EM system responds to bedrock conductors, conductive overburden, and cultural sources. The EM inphase and quadrature data were drift corrected using base level data collected at high altitude (areas of no signal). Along-line filters are applied to the data to remove spheric spikes. The data were inspected for variations in phase, and a phase correction was applied to the data if necessary. Apparent resistivities were then calculated from the inphase and quadrature data for all frequencies based on a pseudo-layer half-space model. Manual leveling of the inphase and quadrature of each coil pair, based on the resistivity data and comparisons to the data from the other frequencies, was performed. Automated micro-leveling is carried out in areas of low signal. The EM data were interpolated onto a regular 80-m grid using a modified Akima (1970) technique. The resulting grids were subjected to a 3x3 hanning filter and resampled to a 25-m cell size before contouring and map production.
Akima, 1970
2007
To produce the digital elevation model, the GPS-Z data were differentially corrected and transformed into the local datum. The ALTBIRD data were filtered using a 13, 13 filter. Both the Z-COR (differentially corrected GPS-Z) was checked for spikes, which were removed manually. The corrected altimeter was then subtracted from the Z-COR data to produce profiles of the height above mean sea level along the survey lines. The data were manually leveled to remove any errors between lines. After all leveling, the data were DC shifted to match the local maps, in this case, NAD27. The final Z value is recalculated as final Z = DEM + altbird. The 80-m DEM grid was then resampled to a 25-m cell size to produce the DEM grid contained on this publication.
2007
The included plot files of the maps were produced by Fugro Airborne Surveys. The HPGL2 files were created with HP Designjet 5000 printer driver v5.32 and will not work with all plotters, but do plot on the DGGS HP Design Jet 5000. The HPGL2 files have brighter colors and sharper topography than the Adobe Acrobat files. The Adobe Acrobat format files were created with Adobe Acrobat Distiller v7.0 (PDF 1.3) from Postscript files. The Postscript files were produced by Hewlett Packard Designjet 5000 Postscript 3 printer driver v4.293 and are not included on this publication.
2007
Universal Transverse Mercator
7
0.9996
-141
0
500000
0
row and column
25
25
meters
North American Datum of 1927
Clarke 1866
6378206.4
294.978698
Entities (file names) are listed in the "GPR2008-1Readme.pdf" file included on this DVD. Attributes recorded during the geophysical survey are listed with the units in the text files "linedata/Fortymile-Linedata.txt". Further description is available in the descriptive project report included in this publication.
L.E. Burns, Division of Geological & Geophysical Surveys and Fugro Airborne Surveys
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
Natural Resource Technician
mailing and physical address
3354 College Road
Fairbanks
AK
99709-3707
USA
907-451-5020
None available
907-451-5050
dggspubs@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays
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.
Geophysical Report 2008-1
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 (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard.
Variable
Geosoft binary float (GRD)
Unknown
DVD
ISO9660 or Joliet
ER Mapper binary (ERS)
Unknown
DVD
ISO9660 or Joliet
Geosoft ASCII (XYZ)
Unknown
DVD
ISO9660 or Joliet
DXF
2000
DVD
ISO9660 or Joliet
HPGL/2 (PRN)
Unknown
DVD
ISO9660 or Joliet
PDF
1.3
http://www.dggs.alaska.gov/pubs/geophysics
DVD
ISO9660 or Joliet
Postscript (PS)
Unknown
DVD
ISO9660 or Joliet
Digital files on DVD are available for $15 plus shipping; currently, only the maps can be downloaded from our web site (http://www.dggs.alaska.gov) and are in PDF format. No fees charged for downloaded files.
Order by phone (907-451-5020), e-mail (dggspubs@alaska.gov), 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/pubs/geophysics) has geophysical order forms for this project and others. Payment accepted: Cash, check, money order, VISA, or MasterCard.
Digital downloads: less than 30 minutes for most files. Offline CD/DVD-ROMs: 1-2 weeks unless special arrangements are made and an express fee is paid.
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.
Software with ability to use, import, or convert Geosoft .grd or ER Mapper .ers 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 HPGL/2 files using HP 5000 series plotters or the Adobe Acrobat files. The HPGL/2 files will provide the clearest hard copy versions. "Printfile" (http://www.lerup.com/printfile/) is a freeware MS Windows utility program that will enable you to print HPGL/2 files; the plotter will still need to be compatible with files produced for the HP 5000 series.
20080506
20080506
2011116
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
Geophysicist
mailing and physical address
3354 College Road
Fairbanks
AK
99709-3707
USA
907-451-5021
None available
907-451-5050
dggspubs@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays.
Please contact us through the e-mail address above whenever possible.
FGDC Content Standards for Digital Geospatial Metadata
FGDC-STD-001-1998
local time
none
If the user has modified the data in any way the user is obligated to describe the types of modifications the user has made in the supporting metadata file. User specifically agrees not to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys.