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Composite and Merged Aeromagnetic Data for Alaska - A Web Site for Distribution of Gridded Data and Plot Files

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Metadata:

Identification_Information
Data_Quality_Information
Spatial_Data_Organization_Information
Spatial_Reference_Information
Entity_and_Attribute_Information
Distribution_Information
Metadata_Reference_Information

Identification_Information:

Citation:

Citation_Information:

Originator: Richard W. Saltus

Publication_Date: 1997

Title:

Composite and Merged Aeromagnetic Data for Alaska - A Web Site for Distribution of Gridded Data and Plot Files

Geospatial_Data_Presentation_Form: remote-sensing image

Series_Information:

Series_Name: U.S. Geological Survey Open-File Report
Issue_Identification: 97-520

Publication_Information:

Publication_Place: Denver, CO
Publisher: U.S. Geological Survey

Online_Linkage: <http://pubs.usgs.gov/of/1997/ofr-97-0520/>

Description:

Abstract:: Data from 85 individual aeromagnetic surveys were merged together to produce a single data grid spanning much of Alaska.
Purpose:: Presentation of gridded aeromagnetic data values for use in geological and geophysical studies.
Supplemental_Information:: This file defines the background of the grid that was used to create the image displayed on the website. The geo-tiff image with a subtle light/dark color scale was created using the commercial software package Geosoft. The resolution is 200 dpi.
Note that grid origin is at the center of the SW grid cell (first value in the grid file). The location of this point is at X=-902,000 and Y=110,000 meters relative to the projection described below.

Time_Period_of_Content:

Time_Period_Information:

Range_of_Dates/Times:

Beginning_Date: 1945
Ending_Date: 1982

Currentness_Reference: ground condition

Status:

Progress: Complete
Maintenance_and_Update_Frequency: None planned

Spatial_Domain:

Bounding_Coordinates:

West_Bounding_Coordinate: -170
East_Bounding_Coordinate: -130
North_Bounding_Coordinate: 71
South_Bounding_Coordinate: 54

Keywords:

Theme:

Theme_Keyword_Thesaurus: None
Theme_Keyword: Aeromagnetic data

Place:

Place_Keyword_Thesaurus: None
Place_Keyword: Alaska

Access_Constraints: None

Use_Constraints: None

Point_of_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Robert P. Kucks
Contact_Organization: U.S. Geological Survey

Contact_Address:

Address_Type: mailing address
Address:: USGS, Box 25046, Mail Stop 964
Denver Fed Center
City: Denver
State_or_Province: CO
Postal_Code: 80225-0046
Country: USA

Contact_Voice_Telephone: (303) 236-1405

Contact_Electronic_Mail_Address: rkucks@usgs.gov

Browse_Graphic:

Browse_Graphic_File_Name: <http://pubs.usgs.gov/of/1997/ofr-97-0520/gif/big_map.gif>
Browse_Graphic_File_Description:: Reduced-size image of the entire state grid, 2213x1614 pixels, 451k bytes.
Browse_Graphic_File_Type: GIF

Data_Set_Credit:

Data were collected between 1945 and 1982 by the U.S. Geological Survey and by private contractors under contract to the U.S. Geological Survey and other government organizations.

Native_Data_Set_Environment:

At the USGS, these data are stored in several binary gridded data formats on unix systems. Data have been distributed in GEOSOFT GXF (an ASCII interchange format), Arc/Info export (e00), and ER Mapper binary formats.

Data_Quality_Information:

Attribute_Accuracy:

Attribute_Accuracy_Report:: Grid values represent the total intensity of the Earth's magnetic field after removal of the International Geomagnetic Reference Field (IGRF). Measurements were made by a variety of magnetometer systems with typical accuracy of 1 to 10 nanotesla (nT).
In addition to corrections for the IGRF, the individual magnetic surveys typically contain corrections for the diurnal variations of the Earth's magnetic field that occurred during the flight (as recorded by a base station magnetometer) and leveling adjustments made at flightline intersections. The absolute accuracy of the gridded data are probably better than 5 nanotesla, with accuracy increasing for with increasing wavelength.

Positional_Accuracy:

Horizontal_Positional_Accuracy:

Horizontal_Positional_Accuracy_Report:

Horizontal position of the aircraft were determined by various means. Older surveys (1945-1960s) were positioned by reconciling down-looking photographs with topographic maps and orthophoto quad maps. Later surveys used various standard aircraft navigation aids as they became available.

Quantitative_Horizontal_Positional_Accuracy_Assessment:

Horizontal_Positional_Accuracy_Value: 500
Horizontal_Positional_Accuracy_Explanation: meters

Vertical_Positional_Accuracy:

Vertical_Positional_Accuracy_Report:

The individual aeromagnetic surveys that make up this data set were flown at various fixed barometric altitudes and as draped surveys with constant terrain clearance specifications.

Quantitative_Vertical_Positional_Accuracy_Assessment:

Vertical_Positional_Accuracy_Value: 100
Vertical_Positional_Accuracy_Explanation: meters

Lineage:

Process_Step:

Process_Description:

Collection of aeromagnetic data.

The "state-of-the-art" for aeromagnetic data collection changed significantly throughout the data collection period for this data set. Journals such as GEOPHYSICS have periodic articles describing the contemporaneous state of standard procedures.

Process_Date: 1945 to 1982

Process_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Patricia L. Hill
Contact_Organization: U.S. Geological Survey

Contact_Address:

Address: USGS Mail Stop 964
City: Denver
State_or_Province: CO
Postal_Code: 80225-0046
Country: USA
Address_Type: mailing address

Contact_Electronic_Mail_Address: pathill@usgs.gov

Contact_Voice_Telephone: (303) 236-1343

Logical_Consistency_Report:

The flight data collected to generate the final gridded product is dependent on the individual contractor. All corresponding corrections were then made by the contractor and a final data set was presented for gridding. Compositing of the individual surveys was done in an analog process before digitizing. The process of reprojecting the grid does not affect the accuracy of the product.

Completeness_Report:

The best resolution (spacing and flight height) flight data was used to generate the compilation. See corresponding indices in original publications for specifications.

Spatial_Data_Organization_Information:

Direct_Spatial_Reference_Method: Raster

Raster_Object_Information:

Raster_Object_Type: Grid cell
Row_Count: 1716
Column_Count: 2216

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:

Planar:

Map_Projection:

Map_Projection_Name: Albers Conical Equal Area

Albers_Conical_Equal_Area:

Standard_Parallel: 55.
Standard_Parallel: 65.
Longitude_of_Central_Meridian: -151.0
Latitude_of_Projection_Origin: 55.0
False_Easting: 0.
False_Northing: 0.

Planar_Coordinate_Information:

Planar_Coordinate_Encoding_Method: row and column

Coordinate_Representation:

Abscissa_Resolution: 1000
Ordinate_Resolution: 1000

Planar_Distance_Units: meters

Geodetic_Model:

Horizontal_Datum_Name: North American Datum of 1927
Ellipsoid_Name: Clarke 1866
Semi-major_Axis: 6378.20640
Denominator_of_Flattening_Ratio: 294.98

Entity_and_Attribute_Information:

Detailed_Description:

Entity_Type:

Entity_Type_Label: Grid cell
Entity_Type_Definition: Area of the earth's surface represented by an observation

Attribute:

Attribute_Label: Residual total intensity of Earth's magnetic field

Attribute_Definition:

Value, in nanotesla, of total intensity of Earth's magnetic field after removal of the theoretical International Geomagnetic Reference Field value.

Attribute_Definition_Source:

Paterson, N.R., and Reeves, C.V., 1985, Applications of gravity and magnetic surveys: The state-of-the-art in 1985: Geophysics, v. 50, p. 2558-2594.

Attribute_Domain_Values:

Range_Domain:

Range_Domain_Minimum: -10,000
Range_Domain_Maximum: 10,000
Attribute_Units_of_Measure: nanotesla
Attribute_Measurement_Resolution: 1-10 nanotesla

Attribute_Domain_Values:

Enumerated_Domain:

Enumerated_Domain_Value: -99999
Enumerated_Domain_Value_Definition: Areas outside the irregular survey boundary

Attribute_Value_Accuracy_Information:

Attribute_Value_Accuracy: 5.0
Attribute_Value_Accuracy_Explanation: nanotesla

Distribution_Information:

Distributor:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Richard W. Saltus
Contact_Organization: U.S. Geological Survey

Contact_Electronic_Mail_Address: saltus@usgs.gov

Contact_Address:

Address_Type: mailing address
Address:: Box 25046, MS 964
Denver Fed Center
City: Denver
State_or_Province: Co
Postal_Code: 80225
Country: USA

Contact_Voice_Telephone: (303) 236-1375

Resource_Description: USGS Open-File Report 97-520

Distribution_Liability:

The USGS has made every effort to verify the veracity of this information, but is not liable for any inaccuracies.

Standard_Order_Process:

Digital_Form:

Digital_Transfer_Information:

Format_Name: Arc/Info export
Format_Version_Number: 7.x
Format_Information_Content:: Gridded files for the Alaska composite (akc*) and merged (akm*) aeromagnetic data. New versions of the grids were added to the web site in February 1999. These grids are akc_msat* and akm_msat*. The new grids contain a regional surface correction based on a satellite magnetic model of the long wavelengths of the Earth's magnetic field (see March 1999 issue of GSA Today for more information). The original grids contained a questionable long-wavelength trend which caused the NW portion of the grids to be tipped downward (there was also a spurious trend with a different slope in SE Alaska).
File_Decompression_Technique: gzip -d
Transfer_Size: 8.7

Digital_Transfer_Option: