USGS Geoscience Data Catalog
Additional USGS Geoscience data can be found by geographic location or by publication series.
U.S. Geological Survey, 2002, Digital data grids for the magnetic anomaly map of North America: U.S. Geological Survey Open-File Report 02-414, U.S. Geological Survey, Denver, Colorado, USA.Online Links:
This is a raster data set. It contains the following raster data types:
The map projection used is Transverse Mercator.
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 1000
Ordinates (y-coordinates) are specified to the nearest 1000
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is sphere.
The semi-major axis of the ellipsoid used is 6371204.0.
The flattening of the ellipsoid used is 1/0.926.
NAmag_origmrg.grd = 232,371 KB NAmag_origmag.grd.gi = 21 KB NAmag_hp500.grd = 232,753 KB NAmag_hp500.grd.gi = 22 KB NAmag_CM.grd = 232,557 KB NAmag_CM.grd.gi = 22 KB
Value | Definition |
---|---|
-1.0E+32 | missing data |
Range of values | |
---|---|
Minimum: | -22711.6 |
Maximum: | 27553.6 |
Units: | nanoteslas |
Resolution: | 1-10 nanoteslas |
Value | Definition |
---|---|
-1.0E+32 | missing data |
Range of values | |
---|---|
Minimum: | -22729.3 |
Maximum: | 27565.8 |
Value | Definition |
---|---|
-1.0E+32 | missing data |
Range of values | |
---|---|
Minimum: | -22724 |
Maximum: | 27541 |
North American Magnetic Anomaly Group (NAMAG)
Viki Bankey (USGS) Alejandro Cuevas (CRM) David Daniels (USGS) Carol A. Finn (USGS) Israel Hernandez (CRM) Patricia Hill (USGS) Robert Kucks (USGS) Warner Miles (GSC) Mark Pilkington (GSC) Carter Roberts (USGS) Walter Roest (GSC) Victoria Rystrom (USGS) Sarah Shearer (USGS) Stephen Snyder (USGS) Ronald Sweeney (USGS) Julio Velez (CRM) Jeffrey Phillips (USGS) D.K.A. Ravat (Southern Illinois University)
303-236-1405 (voice)
rkucks@usgs.gov
This integrated, readily accessible, modern digital database of magnetic anomaly data will be a powerful tool for further evaluation of the structure, geologic processes, and tectonic evolution of the continent and may also be used to help resolve societal and scientific issues that span national boundaries. The North American magnetic anomaly map derived from the digital database provides a comprehensive magnetic view of continental-scale trends not available in individual data sets, helps link widely separated areas of outcrop, and unifies disparate geologic studies.
U.S. Geological Survey, Consejo de Recursos Minerales, Geological Survey of Canada, and North American Magnetic Anomaly Group, 2002, Magnetic Map of North America: U.S.Geological Survey Special Map Magnetic Anomaly Map of North America, U.S. Geological Survey, Denver, Colorado, USA.Online Links:
U.S. Geological Survey, and National Geophysical Data Center, 2002, Digital aeromagnetic data sets of the Conterminous United States and Hawaii: U.S. Geological Survey Open-File Report 02-361, U.S. Geological Survey, Denver, CO, USA.Online Links:
U.S. Geological Survey, 1999, Digitized Aeromagnetic datasets for the conterminous United States, Hawaii, and Puerto Rico.: U.S. Geological Survey Open-File Report 99-557, U.S. Geological Survey, Denver, CO.Online Links:
Grid values represent the total intensity of the Earth's magnetic field
after removal of the International Geomagnetic Reference Field (IGRF).
Measurements were made using a variety of magnetometer systems with
typical accuracies of 1 to 10 nanotesla (nT).
The grids presented in this report were made from numerous individual
grids that were mathematically merged together using standard
techniques. Individual metadata files exist for USGS gridded
data created from digital flight-line data (USGS Open-File Report 02-0361).
The data in the original grids have been processed using formulas and
methods that are not usually documented but that represent
industry standard practices for airborne data reduction.
Flight Path Recovery - before about 1975
Horizontal position of the survey aircraft used to collect
data were determined by reconciling down-looking photographs
(recorded on continuous-strip film) with topographic maps
and orthophotoquadrangle maps. Fiducial numbers and marks,
impressed on any paper strips that were recording data or
added to magnetic tape records, were included
as a function of time to further reconcile location with
instrumentation.
Flight Path Recovery - before about 1990
Horizontal position of the survey aircraft used to collect
data were determined using aircraft navigational aids such
as line-of-sight electronic systems that measure the
distances from each of two ground stations to the aircraft
using microwave or radio transmitters.
Flight Path Recovery - after about 1990
Horizontal position of the survey aircraft used to collect
data were determined using GPS satellite navigation.
The aircraft vertical position was determined using the
navigational positioning equipment on the aircraft, which
were radar altimeter and barometric altimeter.
Radar altimeters are estimated to have an error
of 2-5% of the altitude (Richard Hansen, PRJ, Inc.,
written communication).
Barometric altimeters are quite accurate, but are
typically operated in an uncorrected mode. The
diurnal variation in air pressure over the course of
a flight can produce a 50-100 ft error in the
barometric altimeter reading. In addition, pressure microcells
create short-period air pressure changes equivalent
to about 10 ft under typical conditions (Richard
Hansen, PRJ, Inc., written communication)
The magnetometer was carried on a "stinger" that was attached
to the aircraft or was carried in a bird towed on a
line that was below the aircraft. The bird as it is towed is
slightly behind the aircraft and therefore the vertical
distance between the magnetometer and the aircraft is slightly
less than the length of the line but remains constant for
the survey.
Data were either collected at a fixed barometric altitude or
were collected as a draped survey having an average terrain
clearance above the ground. Because aircraft,
especially airplanes, cannot safely maintain a constant
terrain clearance, error in vertical position is
introduced.
The North American Magnetic Anomaly grids were compiled from the best available aermomagnetic surveys publicly available in 2002. Best available would be data having the highest resolution, closest line-spacing, most accurate instrumentation, most accurate flight-elevation surface, and similar specifications commonly used in the airborne surveying industry. In many areas, only one survey was available. In many offshore areas and some onshore areas, no data were available at all, and these areas were left blank.
The data in this file were collected by various contractors or groups
who were responsible for collecting and processing the data.
The data used to make these grids were collected using different instruments
(magnetometers, altimeters, navigational systems) throughout
the survey, but were usually consistent within each survey.
Survey contracts specified the conditions and specifications under which
these data were collected. Standard industry practices of the time
were followed in data collection and processing.
Are there legal restrictions on access or use of the data?
- Access_Constraints: none
- Use_Constraints: none
303-202-4700 (voice)
<http://www.usgs.gov/pubprod>
USGS Open-File Report OFR 02-0414
Although all data published in these grids have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Data format: | Residual total intensity of Earth's magnetic field in format Geosoft binary grid a 512 byte header followed by grid data Size: 232 megabytes |
---|---|
Network links: |
<ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/NAmag_origmrg.grd> <ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/NAmag_origmrg.gi> |
Data format: | 500-km high-pass filtered grid calculated from residual magnetic grid in format Geosoft binary grid a 512 byte header followed by grid data Size: 232 megabytes |
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Network links: |
<ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/NAmag_hp500.grd> <ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/NAmag_hp500.gi> |
Data format: | Equivalent-source corrected grid in format Geosoft binary grid a 512 byte header followed by grid data Size: 232 megabytes |
---|---|
Network links: |
<ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/NAmag_CM.grd> <ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/NAmag_CM.gi> |
Data format: | Residual total intensity of Earth's magnetic field, showing only the United States in format Geosoft binary grid a 512 byte header followed by grid data Size: 34 megabytes |
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Network links: |
<ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/USmag_origmrg.grd> <ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/USmag_origmrg.gi> |
Data format: | 500-km high-pass filtered grid calculated from residual magnetic grid, showing only the United States in format Geosoft binary grid a 512 byte header followed by grid data Size: 34 megabytes |
---|---|
Network links: |
<ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/USmag_hp500.grd> <ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/USmag_hp500.gi> |
Data format: | Equivalent-source corrected grid, showing only the United States in format Geosoft binary grid a 512 byte header followed by grid data Size: 34 megabytes |
---|---|
Network links: |
<ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/USmag_CM.grd> <ftp://musette.cr.usgs.gov/pub/open-file-reports/ofr-02-0414/USmag_CM.gi> |
303-236-1348 (voice)
viki@usgs.gov