USGS Geoscience Data Catalog
Additional USGS Geoscience data can be found by geographic location or by publication series.
U.S. Geological Survey, and National Geophysical Data Center, 2001, Aeromagnetic data for East Boulder Creek, Montana:.This is part of the following larger work.
U.S. Geological Survey, and National Geophysical Data Center, 2001, Digital flight-line aeromagnetic data sets of the Conterminous United States, Hawaii, and Puerto Rico: U.S. Geological Survey Open-File Report 02-361, U.S. Geological Survey, Denver, CO.
This is a point data set.
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest .0001. Longitudes are given to the nearest .0001. Latitude and longitude values are specified in decimal degrees.
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6,378,206.4.
The flattening of the ellipsoid used is 1/294.98.
Airborne survey specifications These items are constant for the entire survey Project number: 4202 Project name: East Boulder Creek, Montana Survey flown by: Era Aviation Survey compiled by: Geoterrex-Dighem Survey flown for: U.S. Geological Survey Approx. no. of line miles: 188 Survey height: 100 ft Altitude method: Draped over terrain Flight-line spacing: 0.125 mi Flight-line direction: NW-SE Aircraft used: Aerospatiale AS350B2 Airport - arrival: unknown Airport - departure: unknown Magnetometer used: Scintrex MEP710 optically pumped cesium vapor Sensor tow distance: approximately 66 ft
Each record contains the following 11 attributes: No abbrev.name contents 1 line_no flight line number 2 directn flight line direction, azimuth degrees from north (integer) 3 longitud longitude (decimal degrees) 4 latitude latitude (decimal degrees) 5 year year flown (integer) 6 jul_day Julian day flown (integer) 7 fiducial fiducial number (integer) 8 radar radar altimeter reading above ground (feet) 9 barom altitude above mean sea level (feet) 10 totmag corrected magnetic value (nT) 11 resmag residual magnetic value (nT)
Range of values | |
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Minimum: | 10 |
Maximum: | 9030 |
Units: | alphanumeric value |
Range of values | |
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Minimum: | -1 |
Maximum: | -1 |
Units: | degrees |
Range of values | |
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Minimum: | -112.1886 |
Maximum: | -112.0588 |
Units: | decimal degrees |
Range of values | |
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Minimum: | 46.3185 |
Maximum: | 46.4974 |
Units: | decimal degrees |
Range of values | |
---|---|
Minimum: | 1997 |
Maximum: | 1997 |
Range of values | |
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Minimum: | 287 |
Maximum: | 287 |
Range of values | |
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Minimum: | 1652 |
Maximum: | 59470 |
Range of values | |
---|---|
Minimum: | 159 |
Maximum: | 1816 |
Units: | feet |
Range of values | |
---|---|
Minimum: | -9999.9 |
Maximum: | -9999.9 |
Units: | feet |
Range of values | |
---|---|
Minimum: | 43952.9 |
Maximum: | 57335.9 |
Units: | nanoTeslas |
Range of values | |
---|---|
Minimum: | -9878.3 |
Maximum: | 723.4 |
Units: | nanoTeslas |
These USGS employees contributed to reformatting and archiving these data:
Viki Bankey, Carol Finn, Pat Hill, Holly Hindle, Bob Kucks, Vicki Rystrom, Sarah Shearer
Cooperating contributors from the National Geophysical Data Center are:
Ronald Buhmann, David Dater, Susan McLean, Stewart Racey
303-236-1343 (voice)
grav_mag@usgs.gov
Aeromagnetic surveys are used for geophysical prospecting. Some variations in magnetic measurements are caused by rocks that contain significant amounts of magnetic minerals (magnetite being the most common). These anomalies reflect variations in the amount and type of magnetic material and the shape and depth of the body of rock. Aeromagnetic anomaly maps are important tools in mapping surficial and buried igneous rocks. The features and patterns of aeromagnetic anomalies can also be used to delineate details of subsurface geology including the locations of buried faults and the thickness of surficial sedimentary rocks.
U.S. Geological Survey, 1999, Digitized Aeromagnetic Datasets of 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:
Smith, B.D., Labson, V.F., and Hill, P.L., 2000, Airborne geophysical surveys in the Boulder Watershed, Jefferson and Lewis and Clark Counties, Montana: U.S. Geological Survey Open-File Report 00-240, U.S. Geological Survey, Denver, CO.
The data in this file have been processed using various formulas and
methods that are not usually documented but that represent
industry standard practices for airborne data reduction. For example,
position is listed as latitude and longitude, but these values
were derived from the raw navigation data depending on the system used.
(see notes under horizontal accuracy). Line numbers were added to
records, and unusable data at flight-line ends were discarded
(as aircraft slowed and turned around). Separate recordings were
correlated by time and assigned to the correct location.
The exact accuracies of these processing steps may not be known.
They are discussed in the sections on attribute or positional
accuracies.
Flight Path Recovery
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 in a bird towed on a
line that was approximately 66 feet 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.
This data set was collected at a draped survey having a
average terrain clearance of 100 ft. Because aircraft,
especially airplanes, cannot safely maintain a constant
terrain clearance, error in vertical position is
introduced.
Loss of data due to poor transmission, channel dropout, obvious spiking,
missing channels, and other obvious errors were replaced with the
value -9999.9, such as in the barom channel.
The values in the fiducial (fiducial) channel were multiplied by 10 in
order to conform to the established template.
A constant of 20,000 was subtracted from the values in the line number
(line_no) channel in order to conform to the established template.
The original contractor database did not have flight line direction
(directn) or barometric altimeter (barom) channels. A dummy value of -1
was used in the directn channel created during USGS processing in order to
conform to the established template.
The tie lines (9010) were truncated to keep the scale of the database to
an appropriate range. They extended to the west in the contractor's
original database. Tie line 9010 was truncated at -113.1870 degrees W,
tie line 9020 was truncated at -112.1490 degrees W, and tie line 9030 was
truncated at -112.1070 degrees W.
The data in this file were collected by a single contractor or group
who were responsible for collecting and processing the data.
The data from this survey were collected using the same instruments
(magnetometers, altimeters, navigational systems) throughout
the survey and were collected in a normal length of time with no long
delays between survey beginning and end.
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.
The original contractor database has UTM values only. Based on the
contractor report and USGS personnel experience, the values were
projected to the latitude and longitude coordinates included in the
database using the following parameters:
Datum: NAD27
Projection: Clark 1866
UTM Zone 12N (Central Meridian of -111 degrees west longitude)
Are there legal restrictions on access or use of the data?
- Access_Constraints: none
- Use_Constraints:
- none. Acknowledgement of the U.S. Geological Survey and the National Geophysical Data Center would be appreciated in products derived from these data.
303-202-4700 or 1-888-ASK-USGS (voice)
www.usgs.gov/pubprod
USGS Open-File Report OFR 02-0361
Although all data published on this CD-ROM 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: |
Magnetic anomaly measurements
in format ASCII
Each line contains data in the following format, beginning with line 1(no header included): line_no I5 directn I4 longitud F11.4 latitude F9.4 year I5 jul_day I4 fiducial I7 radar F8.1 barom F8.1 totmag F9.2 resmag F9.2, 1X |
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Media you can order: |
CD-ROM
(format ISO 9660)
|
CD-ROM prices are subject to change. Please call or see <http://mapping.usgs.gov/esic/prices/>
Detailed instructions can be found at www.usgs.gov/pubprod
303-236-5486 (voice)
USGS Open-File Report OFR 02-0361
Although all data published on this CD-ROM 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: |
Magnetic anomaly measurements
in format ASCII
Each line contains data in the following format, beginning with line 1 (no header included): line_no I5 directn I4 longitud F11.4 latitude F9.4 year I5 jul_day I4 fiducial I7 radar F8.1 barom F8.1 totmag F9.2 resmag F9.2, 1X |
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Network links: |
<ftp://ftpmusette.cr.usgs.gov/pub/NA_MAGNETICS/digital_data/MT/MT_4202.xyz.gz> |
303-236-1343 (voice)
grav_mag@usgs.gov