Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field intensity values and location. In surveys such as this one where the data were originally collected in digital form and not digitized from contour maps, the information we provide typically includes latitude, longitude, magnetic anomaly in nanoTeslas, and intermediate values used to derive the magnetic anomaly such as total magnetic field.
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.
Reduced-size image depicting the data, 3096 x 1656 pixels, 739,844 bytes
A preliminary data grid has a grid cell size of 350 meters (1150 feet). Final data processing and quality control have not been applied to these data. The purpose of this preliminary data release is to allow prompt public access to these data, which are of interest for active mineral exploration in the region. A more complete data release and description will be published later once the final data processing is complete.
In general each original survey was collected by a single contractor, who would be responsible for processing the field observations, and reflect industry standard practices and controls. Variation among surveys is possible, especially if they were carried out during very different time periods.
of 4,857,396 flight-line points, 11,025 contain missing values, each represented by an asterisk
Detailed positional information is determined by the contractor using navigational controls to specifications given in the contractor reports. Generally these are more precise and accurate for newer surveys than for older ones.
The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter.
The Taylor Mountains aeromagnetic survey was flown in April and May 2004 by McPhar Geosurveys Ltd. under contract to the USGS. The flight lines are oriented northwest to southeast with an interline spacing of 1,600 meters (1 mile). Tie lines were flown in a perpendicular direction (northeast to southwest) with spacing of 12,900 meters (8 miles). The survey flights were 2USGS Open-File Report 20041293 Taylor Mountains, Alaska, preliminary aeromagnetics draped over topography using a preplanned flight surface with a nominal clearance of 305 meters (1,000 feet). Care was taken to avoid data collection during periods of intense diurnal disturbance of the Earths magnetic field. Differential Global Positioning System (GPS) was used for flight navigation.
This data grid is based on minimum curvature gridding of preliminary flight-line data. Data processing at this stage includes field corrections and office corrections. In the field: (1) Compensation for the airplane magnetic field, (2) heading correction (for the influence of the direction in which the magnetic sensor is traversing the Earths magnetic field), (3) lag correction (compensation for the difference of position between the GPS and magnetic sensors). In the office: (4) Tie-line leveling, (5) International Geomagnetic Reference Field (IGRF) removal using IGRF 2000, and (6) microleveling to remove residual flight-line artifacts. Note that base station magnetic data were recorded at several field sites but have not yet been processed or applied to the preliminary data grid.
The data have not been subjected to contractor or USGS quality-control checks. The data appear consistent with previous aeromagnetic data and grids for this region (Saltus and Simmons, 1997). The grid is projected using the WGS 84 datum and Universal Transverse Mercator Zone 4. The X location of the bottom-left grid data point is 447,300 meters. The Y location of the bottomleft grid data point is 6,647,200 meters. There are 635 columns (west to east) and 346 rows (south to north) in the data grid. Each grid cell is 350 meters on a side.
Contact_Organization:U.S. Geological Survey, Mineral Resources Program Contact_Person:Richard W. Saltus
Address_Type:mailing address Address:
Mail Stop 964 Building 20 Denver Federal Center, West 6th Avenue and Kipling Streets
Reference herein to any specific commercial product, process, or service by trade name,trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.