Title:Airborne geophysical survey: Trinity Valley, New Mexico Abstract:
Aeromagnetic data were collected along flight lines by instruments in an
aircraft that recorded magnetic-field values and locations. In the earlier
days of surveying, the only way to represent this data was to generate an
analog map with contour lines. This dataset is a representation of the
digitized contour lines either by following the lines or by choosing the
intersection of the contour and flight-line to create a value of the magnetic
field. The values presented are latitude, longitude, and map magnetic-field
What coordinate system is used to represent geographic features?
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude.
Latitudes are given to the nearest 0.0001.
Longitudes are given to the nearest 0.0001.
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: NM02
Project name: Trinity Valley
Survey flown by: U.S. Navy
Survey flown for: U.S. Department of Defense
Approx. no. of line miles: 550
Survey height: 5600 ft
Altitude method: Above sea level
Flight-line spacing: 0.5 mi
Flight-line direction: N-S
Aircraft used: unknown
Airport - arrival: unknown
Airport - departure: unknown
Sensor tow distance: unknown
Magnetometer used: unknown
Data recording interval: unknown
Regional field removed: unknown
Nettleton, L.L., 1971, Elementary Gravity and Magnetics for
Geologists and Seismologists: Society of Exploration Geophysicists
Monograph Series No. 1.
Dobrin, M.B., 1976, Introduction to Geophysical Prospecting:
New York, McGraw-Hill Book Company
Sheriff, R.E., 1984, Encyclopedic dictionary of exploration
geophysics: Tulsa, OK, Society of Exploration Geophysicists.
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. 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.
Conversion of measured values to geographic position and
magnetic values was performed by the processors using
industry standard practices.
Details are found under Horizontal_Position_Accuracy_Report,
Unless noted, conversion processes were not documented.
Products may include some written documentation.
Date: 2008 (process 2 of 3)
USGS digitized original map to ASCII format.
USGS personnel used the software package Oasis Montaj by
Geosoft, Inc., to read in the ASCII digitized data and create
raster JPEG images.
Date: 10-Nov-2020 (process 3 of 3)
Added keywords section with USGS persistent identifier as theme keyword.
Person who carried out this activity:
NOAA, National Geophysical Data Center, 1984, Composite residual total intensity aeromagnetic map of New Mexico; Overlay 2 in Geothermal Resources of New Mexico: National Geophysical Data Center Scientific Map Series Announcement 84-TGB-05, NOAA, National Geophysical Data Center, Boulder, CO.
How well have the observations been checked?
The data shown on the original map 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.
How accurate are the geographic locations?
Flight Path Recovery
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.
How accurate are the heights or depths?
The aircraft vertical position was determined using the
navigational positioning equipment on the aircraft, which
were radar altimeter and barometric altimeter.
How consistent are the relationships among the observations, including topology?
The data on the original map 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 layout specified the conditions and specifications under which
these data were collected. Standard industry practices of the time
were followed in data collection and processing.
Although all data published on this website 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.
Each line contains data in the following format,
beginning with line 1 (no header included):
longitud F12.4 Longitude in decimal degrees
latitude F12.4 Latitude in decimal degrees
mag F8.1 Magnetic value represented on map. This is the
total field value with an arbitrary datum removed
This dataset was prepared by an agency of the United States
Government. Neither the United States Government nor any agency
thereof, nor any of their employees, make any warranty, expressed or
implied, or assumes any legal liability or responsibility for the
accuracy, completeness, or usefulness of any information, apparatus,
product, or process disclosed in this report, or represents that its
use would not infringe privately owned rights. Reference therein to
any specific commercial product, process, or service by trade name,
trademark, manufacturer, or otherwise does not necessarily constitute
or imply its endorsement, recommendation, or favoring by the United
States Government or any agency thereof. Any views and opinions of
authors expressed herein do not necessarily state or reflect those of
the United States Government or any agency thereof.