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Virginia Downloadable Data Files

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Explanation of grid files: see  grid_facts.txt or grid_facts.doc

State composite residual aeromagnetic grid files for four formats (self-extracting zipped):

     vamag_1000ft_grd.exe 

vamag_500ft_grd.exe 

(Geosoft OasisMontaj binary format)

     vamag_1000ft_gxf.exe 

vamag_500ft_gxf.exe 

(grid exchange ascii format)

     vamag_1000ft_arc.exe 

vamag_500ft_arc.exe 

(ESRI binary format - requires Spatial Analyst)

     vamag_1000ft_usg.exe 

vamag_500ft_usg.exe 

(USGS PC binary grid format)

State complete Bouguer gravity anomaly grid files for four formats (self-extracting zipped):

      vagrav_grd.exe 

 (Geosoft OasisMontaj binary format)

      vagrav_gxf.exe 

 (grid exchange ascii format)

      vagrav_arc.exe 

 (ESRI binary format - requires Spatial Analyst)

      vagrav_usg.exe 

 (USGS PC binary grid format)

State gravity point files (self-extracting zipped):  (29,488 measurements)

      vagrav_asc.exe 

 (ascii formatted listing)

      vagrav_csv.exe 

 (comma separated value format - Excel input)

Metadata Files:

      Files 

 Description

      metadata.txt

 Metadata in text format

      metadata.html

 Metadata in standard html format

      metadata.faq.html

 Metadata in Frequently Asked Questions format

 

Fields for ASCII data files

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

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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U.S. Department of the Interior, U.S. Geological Survey
URL: http://pubs.usgs.gov/of/2005/1052/html/va_data.htm
For more information about this report, please contact Stephen Snyder at ssnyder@usgs.gov.
Maintained by Eastern Publications Group
Last modified: 21:11:12 Sat 12 Jan 2013
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