Entity_and_Attribute_Overview:
Airborne survey specifications
These items are constant for the entire survey
Project number: 4226
Project name: Yamhill-Tillamook, Oregon
Survey flown by: Sander Geophysics, Ltd.
Survey flown for: U.S. Geological Survey
Approx. no. of line miles: 4476
Survey height: 800 ft
Altitude method: Draped over terrain
Flight-line spacing: 0.33 mi
Flight-line direction: E-W
Aircraft used: Cessna 404
Airport - arrival: McNavy Airfield, Salem, OR
Airport - departure: McNavy Airfield, Salem, OR
Magnetometer used: Geometrics G-822A
Sensor tow distance: approximately 8.2 ft (2.5 m)
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.
- record for one magnetic data point
- The set of all measurements reported for a magnetic data point
having the same spatial location.
(Source: Standard aeromagnetic data collection procedures as written in the contract for survey collection.)
- line_no
- flight line number
(Source: often assigned by airborne survey crew)
| Range of values |
|---|
| Minimum: | 1001 |
|---|
| Maximum: | 6300 |
|---|
| Units: | alphanumeric value |
|---|
- directn
- direction of flight line, azimuth degrees
clockwise from north
Value of -1 indicate missing data.
(Source: self evident)
| Range of values |
|---|
| Minimum: | 0 |
|---|
| Maximum: | 270 |
|---|
| Units: | degrees |
|---|
- longitud
- longitude - geographic coordinate
(Source: self evident)
| Range of values |
|---|
| Minimum: | -124.0010 |
|---|
| Maximum: | -123.1616 |
|---|
| Units: | decimal degrees |
|---|
- latitude
- latitude - geographic coordinate
(Source: self evident)
| Range of values |
|---|
| Minimum: | 44.7475 |
|---|
| Maximum: | 45.5160 |
|---|
| Units: | decimal degrees |
|---|
- year
- year of data point collection
(Source: self evident)
| Range of values |
|---|
| Minimum: | 1999 |
|---|
| Maximum: | 1999 |
|---|
- jul_day
- Julian day, where Jan. 1 = 1 and
Dec. 31 = 365 or 366 (leap year)
Value of -99 indicate missing data.
(Source: self evident)
| Range of values |
|---|
| Minimum: | 9 |
|---|
| Maximum: | 45 |
|---|
- fiducial
- 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.
Value of -99999 indicate missing data.
(Source: Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists, p. 89.)
| Range of values |
|---|
| Minimum: | 242720 |
|---|
| Maximum: | 361844 |
|---|
- radar
- 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.
(Source: Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists, p. 89.)
| Range of values |
|---|
| Minimum: | 614.8 |
|---|
| Maximum: | 3126.2 |
|---|
| Units: | feet |
|---|
- barom
- 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.
(Source: self evident)
| Range of values |
|---|
| Minimum: | 433.3 |
|---|
| Maximum: | 4090.8 |
|---|
| Units: | feet |
|---|
- totmag
- 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.
(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.)Frequency of measurement: The magnetometer has a recharging interval of 0.5 seconds. The data were recorded at 0.1 second intervals.
| Range of values |
|---|
| Minimum: | 52911.79 |
|---|
| Maximum: | 55588.88 |
|---|
| Units: | nanoTeslas |
|---|
- resmag
- residual magnetic value
The total magnetic value minus a geomagnetic reference field (GRF),
which is a long-wavelength regional magnetic field. The most commonly
used reference field is determined from a model developed by the
International Association of Geomagnetism and Aeronomy (IAGA). The
International Geomagnetic Reference Field (IGRF), is a predictive model
adopted at the beginning of a model period (e.g. in 1989 for
1990-1995). After the model period, a revised definitive model is
adopted, the DGRF. This is the preferred model to use for removing
regional magnetic fields.
For this survey, the field removed was the IGRF 1995 based on the
location, altitude, and date of each point.
After the IGRF and diurnal was removed, an average datum of 8.49 nT was
added.
Values of -9999.9 indicate missing data.
(Source: Nettleton, L.L., 1971, Elementary Gravity and Magnetics for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series No. 1, p. 83-87.)
| Range of values |
|---|
| Minimum: | -887.89 |
|---|
| Maximum: | 1454.79 |
|---|
| Units: | nanoTeslas |
|---|
