Virginia Downloadable Data Files
Explanation of grid files: see grid_facts.txt or grid_facts.doc
State composite residual aeromagnetic grid files for four formats (self-extracting zipped):
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(Geosoft OasisMontaj binary format) |
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(grid exchange ascii format) |
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(ESRI binary format - requires Spatial Analyst) |
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(USGS PC binary grid format) |
State complete Bouguer gravity anomaly grid files for four formats (self-extracting zipped):
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(Geosoft OasisMontaj binary format) |
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(grid exchange ascii format) |
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(ESRI binary format - requires Spatial Analyst) |
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(USGS PC binary grid format) |
State gravity point files (self-extracting zipped): (29,488 measurements)
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(ascii formatted listing) |
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(comma separated value format - Excel input) |
Metadata Files:
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Description |
Metadata in text format |
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Metadata in standard html format |
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Metadata in Frequently Asked Questions format |
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Fields for ASCII data files |
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| Field | Description |
| 1 | Longitude in degrees |
| 2 | Latitude in degrees |
| 3 | Free-air anomaly in mGal |
| 4 | Complete Bouguer anomaly (density=2.67 g/cm3 ) in mGal |
| 5 | Station elevation in feet |
| 6 | Inner terrain correction (Hammer zones A-F) in mGal |
| 7 | Outer terrain correction (Hammer zones G-O) in mGal |
| 8 | Observed gravity in mGal |
| 9 | Survey source number 1 |
1 Survey source number is a numeric code for the contributing author or organization of each source of gravity data. A brief description of each source number can be found at: http://www.ngdc.noaa.gov/seg/cdroms/grav99v1/data/regional/ngs99/93dmauth.dat. However, some survey source numbers are not listed. The source "md_va" can be found at NGDC's web site listed under "Regional Surveys".
Get free grid display and grid conversion software from Geosoft: Each of the grid file formats may be viewed on-screen or printed using the free OasisMontaj interface software. An important second function of the software is to convert grids to other grid formats such as ER Mapper, Surfer, and USGS. A third function permits downloading North American regional aeromagnetic or gravity grids, world DEM grids, and world coastline and rivers for any map. This free software is available from Geosoft at: http://www.geosoft.com/pinfo/oasismontaj/free/index.asp. Open an instruction file for using the free software.
Other USGS download sites for aeromagnetic data: Ascii files of most digitized USGS analog surveys may be downloaded from: http://pubs.usgs.gov/of/1999/ofr-99-0557/html/mag_home.htm (U.S. Geological Survey, 1999). Digital flight line data for most USGS surveys flown since about 1973 are available from: http://pubs.usgs.gov/of/2002/ofr-02-361 (U.S. Geological Survey and National Geophysical Data Center, 2002).
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