Entity_and_Attribute_Overview:
Airborne survey specifications
These items are constant for the entire survey
Project number: 4004
Project name: Mt. St. Helens, Washington
Survey flown by: Applied Geophysics, Inc.
Survey flown for: U.S. Geological Survey
Approx. no. of line miles: 175
Survey height: 11,500 ft
Altitude method: Constant barometric elevation
Flight-line spacing: 0.62 mi
Flight-line direction: E-W
Aircraft used: Cessna 185
Airport - arrival: unknown
Airport - departure: unknown
Magnetometer used: GeoMetrics G-803
Sensor tow distance: 0
Entity_and_Attribute_Detail_Citation:
Nettleton, L.L., 1971, Elementary Gravity and Magnetics for
Geologists and Seismologists: Society of Exploration Geophysicists
Monograph Series No. 1, p. 83-87.
Dobrin, M.B., 1976, Introduction to Geophysical
Prospecting: New York, McGraw-Hill Book Company,
p. 505-517.
Entity_and_Attribute_Overview:
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)
Entity_and_Attribute_Detail_Citation:
Nettleton, L.L., 1971, Elementary Gravity and Magnetics for
Geologists and Seismologists: Society of Exploration Geophysicists
Monograph Series No. 1, p. 83-87.
Dobrin, M.B., 1976, Introduction to Geophysical
Prospecting: New York, McGraw-Hill Book Company,
p. 505-517.
Entity_Type:
Entity_Type_Label: record for one magnetic data point
Entity_Type_Definition:
The set of all measurements reported for a magnetic data point
having the same spatial location.
Entity_Type_Definition_Source:
Standard aeromagnetic data collection procedures as written in
the contract for survey collection.
Attribute:
Attribute_Label: line_no
Attribute_Definition: flight line number
Attribute_Definition_Source: often assigned by airborne survey crew
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 151
Range_Domain_Maximum: 904
Attribute_Units_of_Measure: alphanumeric value
Attribute:
Attribute_Label: directn
Attribute_Definition:
direction of flight line, azimuth degrees
clockwise from north
Attribute_Definition_Source: self evident
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 0
Range_Domain_Maximum: 270
Attribute_Units_of_Measure: degrees
Attribute:
Attribute_Label: longitud
Attribute_Definition: longitude - geographic coordinate
Attribute_Definition_Source: self evident
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -122.3144
Range_Domain_Maximum: -122.0441
Attribute_Units_of_Measure: decimal degrees
Attribute:
Attribute_Label: latitude
Attribute_Definition: latitude - geographic coordinate
Attribute_Definition_Source: self evident
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 46.1031
Range_Domain_Maximum: 46.2642
Attribute_Units_of_Measure: decimal degrees
Attribute:
Attribute_Label: year
Attribute_Definition: year of data point collection
Attribute_Definition_Source: self evident
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 1979
Range_Domain_Maximum: 1979
Attribute:
Attribute_Label: jul_day
Attribute_Definition:
Julian day, where Jan. 1 = 1 and
Dec. 31 = 365 or 366 (leap year)
Attribute_Definition_Source: self evident
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 278
Range_Domain_Maximum: 278
Attribute_Value_Accuracy_Information:
Attribute_Value_Accuracy: 31
Attribute_Value_Accuracy_Explanation:
Both beginning and end julian
dates were taken from dataset.
Attribute:
Attribute_Label: fiducial
Attribute_Definition:
A fiducial number is a mark which indicates points of
simultaneity. It is a user-defined integer used during
airborne operations to correlate recording devices (magnetometers)
with navigational records (altimeters, camera film, strip charts)
that were recorded at the same time.
Attribute_Definition_Source:
Sheriff, R.E., 1984, Encyclopedic dictionary of
exploration geophysics: Tulsa, OK, Society of
Exploration Geophysicists, p. 89.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 16520
Range_Domain_Maximum: 18141
Attribute:
Attribute_Label: radar
Attribute_Definition:
radar altimetry reading, in feet
An aircraft navigational system in which short electromagnetic waves
are transmitted, and the energy scattered back by reflection
is detected. From this measurement, the distance between the aircraft
and the ground is calculated and recorded as radar altimetry.
Values of -9999.9 indicate missing data.
Attribute_Definition_Source:
Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics:
Tulsa, OK, Society of Exploration Geophysicists, p. 89.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 0
Range_Domain_Maximum: 0
Attribute_Units_of_Measure: feet
Attribute:
Attribute_Label: barom
Attribute_Definition:
altitude above mean sea level, in feet, measured using the
barometer that is part of the aircraft navigation system
Values of -9999.9 indicate missing data.
Attribute_Definition_Source: self evident
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 11098.9
Range_Domain_Maximum: 11299.1
Attribute_Units_of_Measure: feet
Attribute:
Attribute_Label: totmag
Attribute_Definition:
Raw magnetic value with base magnetometer corrections applied.
Because the magnetic field of the earth varies diurnally,
a stationary base magnetometer is maintained on the ground
during airborne surveying. The base magnetometer records
changes in the magnetic field (in nanoTeslas) as a function
of time. The magnetic changes may have an amplitude of 20
to 50 nanoTeslas. If changes are more severe, as would
occur from a magnetic storm, surveying is discontinued or
the data recorded are not used.
Diurnal variations are then removed from the airborne magnetic
data based on the common time.
Values of -9999.9 indicate missing data.
Attribute_Definition_Source:
see: Nettleton, L.L., 1971, Elementary Gravity and Magnetics for
Geologists and Seismologists: Society of Exploration Geophysicists
Monograph Series No. 1, p. 83-87.
A description of magnetometers and how they measure
the total magnetic field can be found in:
Dobrin, M.B., 1976, Introduction to Geophysical
Prospecting: New York, McGraw-Hill Book Company,
p. 505-517.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 55429.19
Range_Domain_Maximum: 56353.84
Attribute_Units_of_Measure: nanoTeslas
Attribute_Value_Accuracy_Information:
Attribute_Value_Accuracy: 2
Attribute_Value_Accuracy_Explanation:
The airborne magnetometer is accurate to about 1 nanoTesla,
and the base magnetometer has the same accuracy. The accuracy
of the base-corrected airborne value therefore is near 2 nanoTeslas
or better.
Attribute_Measurement_Frequency:
The magnetometer has a recharging interval of 0.5
seconds. The data were recorded at 1 second intervals.
Attribute:
Attribute_Label: resmag
Attribute_Definition:
residual magnetic value
The total magnetic value minus a geomagnetic reference field (GRF),
which is a long-wavelength regional magnetic field determined by an
international committee about every five years (e.g., 1965, 1970,
1975, 1980, 1985). The International GRF (IGRF) is commonly used.
After adequate acceptance, a model becomes the Definitive GRF (DGRF),
which is the preferred field to remove.
For this survey, the field removed was the IGRF 1975 updated to the
date flown.
Values of -9999.9 indicate missing data.
Attribute_Definition_Source:
Nettleton, L.L., 1971, Elementary Gravity and Magnetics for
Geologists and Seismologists: Society of Exploration Geophysicists
Monograph Series No. 1, p. 83-87.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -138.12
Range_Domain_Maximum: 798.78
Attribute_Units_of_Measure: nanoTeslas
Attribute_Value_Accuracy_Information:
Attribute_Value_Accuracy: 2
Attribute_Value_Accuracy_Explanation:
The Geomagnetic Reference Field that was subtracted from
the total magnetic value is based on a model, which was
updated to the date of the survey. New models are
available at five year intervals. These models have
varying degrees of accuracy in determining the local
reference field.