Identification_Information: Citation: Citation_Information: Originator: V.E. Langenheim Originator: R.C. Jachens Publication_Date: 2014 Title: Magnetic data, processing, and maps of Fort Irwin and vicinity, southern California Geospatial_Data_Presentation_Form: point digital data Series_Information: Series_Name: Open-File Report Issue_Identification: 2013-1024–I Publication_Information: Publication_Place: Menlo Park, CA Publisher: U.S. Geological Survey Online Linkage: http://pubs.usgs.gov/of/2013/1024/i/ Description: Abstract: Helicopter magnetic data of the Leach Basin area, aeromagnetic data for the Soda Lake region, magnetic gradients, a grid of the detailed aeromagnetic data, and magnetic susceptibility data for Fort Irwin and vicinity, southern California Digital Files: The database includes an ASCII file containing point magnetic data from the Leach Basin helicopter survey, an ASCII file containing point magnetic data from the Soda Lake aeromagnetic survey, a grid of detailed aeromagnetic data from the Fort Irwin region, two ASCII files with point locations of the local maximum horizontal gradient derived from the magnetic grid, and one of magnetic susceptibility data. This metadata file describes the maximum horizontal gradients of the magnetic field. Purpose: Aeromagnetic map identifies magnetic features as a basis for geophysical interpretations; the gradients help define the edges of magnetic sources. Supplemental_Information: This database updates geophysical information originally presented in smaller scale formats and includes detailed helicopter magnetic data collected by Aeroquest International. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 1982 Ending_Date: 2011 Currentness_Reference: publication date Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -117.276 East_Bounding_Coordinate: -116.040 North_Bounding_Coordinate: 35.907 South_Bounding_Coordinate: 34.726 Keywords: Theme: Theme_Keyword: magnetics Theme_Keyword: magnetic anomaly Theme_Keyword: magnetic gradient Place: Place_Keyword: southern California Place_Keyword: Mojave Desert Place_Keyword: Fort Irwin Access_Constraints: none Use_Constraints: Uses of this digital data should not violate the spatial or attribute resolution of the data. Although the digital form of the data stores location and attribute values to several decimals of precision, the data is subject to the accuracy and precision inherent in the data due to data collection and processing limitations. Where this data is used in combination with other data, the precision and accuracy of the resulting dataset is limited by the precision and accuracy of the input datasets. Acknowledgement of the U.S. Geological Survey is appreciated for products derived from these data. Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Victoria Langenheim Contact_Organization: U.S. Geological Survey Contact_Position: geophysicist Contact_Address: Address_Type: physical address Address: 345 Middlefield Rd. City: Menlo Park State_or_Province: CA Postal_Code: 94025 Country: USA Contact_Voice_Telephone: 650-329-5313 Contact_Electronic_Mail_Address: zulanger@usgs.gov Native_Data_Set_Environment: Geosoft Oasis Montaj Native_Data_Set_Environment: ARC/INFO versions 9.0., 9.1, 9.2, and 9.3 Geophysical data was stored and analyzed on a SUN Ultra4000 UNIX platform Geospatial_Data_Presentation_Form: ascii digital data (horizontal magnetic gradients) Series_Information: Series_Name: U.S. Geological Survey (USGS) Open-File Report Issue_Identification: 2012-XXXX Publication_Information: Publication_Place: Menlo Park, California Publisher: U.S. Geological Survey Online_Linkage: Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: maximum horizontal gradient values are reported to 0.000001 nT/km Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: accuracy should be within 250 meters (grid size that gradient was calculated from) Lineage: Process_Step: Process_Description: Maximum horizontal gradient is calculated from the magnetic potential grid derived from the residual magnetic grid Process_Date: 2012 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Point Point_and_Vector_Object_Information: SDTS_Terms_Description: SDTS_Point_and_Vector_Object_Type: Entity point Point_and_Vector_Object_Count: 28328 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.0001 Longitude_Resolution: 0.001 Geographic_Coordinate_Units: Decimal degrees Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1929 Ellipsoid_Name: Clarke 1866 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: mag_grad_big.dat Attribute: Attribute_Label: maximum horizontal gradient Attribute_Definition: location of local maximum horizontal gradient from magnetic potential of aeromagnetic grid (larger than the mean of the entire area) Attribute: Attribute_Label: lon_nad27 Attribute_Definition: longitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250 m Attribute: Attribute_Label: lat_nad27 Attribute_Definition: latitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250 m Attribute: Attribute_Label: gradient_magnitude Attribute_Definition: maximum horizontal gradient Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 0.00001 Entity_Type: Entity_Type_Label: mag_grad_small.dat Attribute: Attribute_Label: maximum horizontal gradient Attribute_Definition: location of local maximum horizontal gradient from magnetic potential of aeromagnetic grid (less than the mean of the entire area) Attribute: Attribute_Label: lon_nad27 Attribute_Definition: longitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250 m Attribute: Attribute_Label: lat_nad27 Attribute_Definition: latitude coordinate Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 250m Attribute: Attribute_Label: gradient_magnitude Attribute_Definition: maximum horizontal gradient Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 0.00001 Distribution_Information: Distributor: U.S. Geological Survey Resource_Description: Downloadable Data Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: ASCII Transfer_Size: 483988 Network_Resource_Name: http://pubs.usgs.gov/of/XXXX Process_Date: 2010-2011 Process_Step: Process_Description: Geophysical mapping The locations of local maximum horizontal gradient of the magnetic field were derived using a compilation of the newly flown aeromagnetic data (this report) and previously published magnetic data. The magnetic data were compiled from existing publications (U.S. Geological Survey, 1985; Roberts and Jachens, 1999; U.S. Geological Survey and National Geophysical Data Center, 2002) and the data were interpolated to a regular grid (Briggs, 1974) with cell dimensions of 250 m in both the X and Y directions. The magnetic base levels were then adjusted to a common magnetic datum used in previous magnetic surveys, with a 1-km gap separating the various surveys. A residual magnetic field was obtained by subtracting the magnetic field upward continued 100 m from the interpolated data. The residual data were mathematically transformed to pseudogravity anomalies (Baranov, 1957). Horizontal maximum gradients were then calculated from the pseudogravity field (Blakely and Simpson, 1986). The two files are mag_grad_big.dat and mag_grad_small.dat. Baranov, V.I., 1957, A new method for interpretation of aeromagnetic maps--pseudo-gravimetric anomalies: Geophysics, v. 22, p. 359-383. Blakely, R.J., and Simpson, R.W., 1986, Approximating edges of source bodies from magnetic or gravity anomalies: Geophysics, v. 51, p. 1494-1498. Briggs, I., 1974, Machine contouring using minimum curvature: Geophysics, v. 39, no. 1, p. 39-48. Roberts, C.W., and Jachens, R.C., 1999, Preliminary aeromagnetic anomaly map of California: U.S. Geological Survey Open-File Report 99-440, 14 p. Also available at http://geopubs.wr.usgs.gov/open-file/of99-440/ (last accessed 8/31/2011). U.S. Geological Survey, 1985, Aeromagnetic map of the Ord Mountains, southern California: U.S. Geological Survey Open-File Report 87-005, 9 sheets, scale 1:62,500. U.S. Geological Survey and National Geophysical Data Center, 2002, Aeromagnetic datasets for the conterminous United States and Hawaii: U.S. Geological Survey Open-File Report 02-361. Available at http://pubs.usgs.gov/of/2002/ofr-02-361/ (last accessed 8/31/2011). Metadata_Reference_Information: Metadata_Date: 20120711 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Victoria Langenheim Contact_Organization: U.S. Geological Survey Contact_Position: geophysicist Contact_Address: Address_Type: mailing and physical address Address: 345 Middlefield Rd. City: Menlo Park State_or_Province: CA Postal_Code: 94025 Contact_Voice_Telephone: 650-329-5313 Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998 Metadata_Time_Convention: local time Metadata_Extensions: Online_Linkage: http://www.esri.com/metadata/esriprof80.html Profile_Name: ESRI Metadata Profile