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Open-File Report 02–361: Readme File
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Version 1.0

By U.S. Geological Survey and National Geophysical Data Center

2002

README.HTML
 

About This DVD

After pioneering the first airborne magnetic survey in 1945, the U.S. Geological Survey  (USGS) has collected piecemeal aeromagnetic data for most of the U.S., including offshore areas on both coasts. The U.S. Geological Survey's digital and analog archives comprise more than 1,000 surveys, covering approximately 8,000,000 line-km of data, flown at various flight heights and line spacings.  The purpose of this report is to compile and standardize original aeromagnetic survey data (approximately 5,800,00 line-km) and make them available to the public.

This DVD contains currently available digital magnetic files for the conterminous U.S. and Hawaii from the USGS archives.  Updates and corrections to files included here can be found on the online release of the datasets (https://pubs.usgs.gov/of/2002/ofr-02-361).

Data Format for ASCII .XYZ Files

Format
FORTRAN ASCII data formats specified as follows:  I = integer, F = floating point.  Column widths given as total width and number of decimal points

Example of .XYZ file format

    2 270   -89.2373  41.5869 1981 100   1520   994.1  1791.3 57483.93     4.96
    2 270   -89.2380  41.5869 1981 100   1530   984.3  1791.3 57483.18     4.10
    2 270   -89.2386  41.5869 1981 100   1540   984.3  1791.3 57483.43     4.37
    2 270   -89.2392  41.5869 1981 100   1550   987.5  1768.4 57481.93     2.91

Line_no (I5)
Directn (I4) - flight line direction, azimuth degrees clockwise from north
Longitude (F11.4) - decimal degrees
Latitude (F9.4) - decimal degrees
Year (I5)
Jul_day (I4) - Julian day
Fiducial (I7)
Radar (F8.1) - radar altimeter reading, in feet
Barom (F8.1) - barometric altimeter reading, in feet
Totmag (F9.2) - total magnetic value, diurnally corrected, in nT
Resmag (F9.2) - total magnetic value minus a Geomagnetic Reference Field (GRF), in nT
1X

NOTE: longitude and latitude are defined to four decimal places (10 meter resolution) because this is the most reasonable accuracy that can be standardized for the variety and scaling of many of the original maps.

A Geosoft import template (import_template.i3) is available on the ftp site (ftp://ftpext.usgs.gov/pub/cr/co/denver/musette/pub/NA_MAGNETICS/digital_data).

Processing Specifications (.XYZ and .JPG)

Digital databases were imported, edited in a cursory fashion, and exported using Geosoft Oasis montaj software, version 4.3 and higher.  Errors may still remain.  A standardized template was created (format above) from which all .XYZ files were exported.  *.JPG images of the data were created using a Geographic Coordinate (longitude, latitude) System and the Clarke 1866 datum.  Specific processing information, including types and extent of editing and processing, errors still present in data, application of Geomagnetic Reference Field (GRF), are given in the corresponding metadata file for each survey.
 

Format for Metadata Files

The format for metadata files is based on the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata.  Metadata files are also included at the National Geospatial Data Clearinghouse, but repeated here for convenience and association with survey .XYZ files and .jpg images.

How to Run This DVD

  • Load the DVD and read the readme file. Change the directory to E:\ (E is assumed to be the users DVD reader).
  • If you are running this DVD on a PC using Windows 95, 98, 2000, NT, ME, or XP or on a Macintosh, simply double click on the file named "mag_home.htm".
  • For UNIX and Windows 3.x systems, load your browser into memory and then execute the "mag_home.htm" file.

NOTE: This DVD was developed on a Pentium III PC using the Hyper Text Markup Language.  In theory because this is an HTML product, it should run on most platforms using various browsers.
 

If you have any questions about or problems with the data on this DVD, please contact Pat Hill or Bob Kucks.

* This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Use of brand names is for descriptive purposes and does not constitute endorsement by the U.S. Geological Survey.
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