Identification_Information: Citation: Citation_Information: Originator: U.S. Geological Survey Publication_Date: 2006 Title: Texas Aeromagnetic and Gravity Maps and Data- A Website for Distribution of Data Geospatial_Data_Presentation_Form: raster digital data Series_Information: Series_Name: U.S. Geological Survey Data Series Issue_Identification: 232 Publication_Information: Publication_Place: Denver, Colo., USA Publisher: U.S. Geological Survey Description: Abstract: This report contains digital data, image files, and text files describing data formats for aeromagnetic and gravity data used to compile the State aeromagnetic and gravity maps of Texas. Purpose: The overall objective of these surveys is to improve knowledge of the subsurface geologic framework as part of multi- disciplinary and multi-agency efforts. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 1967 Ending_Date: 2001 Currentness_Reference: publication date Status: Progress: complete Maintenance_and_Update_Frequency: none planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -107.0 degrees W. longitude East_Bounding_Coordinate: -93.5 degrees W. longitude North_Bounding_Coordinate: 36.5 degrees N. latitude South_Bounding_Coordinate: 25.88 degrees N. latitude Keywords: Place: Place_Keyword_Thesaurus: none Place_Keyword: United States Place_Keyword: Texas Theme: Theme_Keyword_Thesaurus: none Theme_Keyword: aeromagnetic data Theme_Keyword: geophysical data Theme_Keyword: aeromagnetic grid Access_Constraints: none Use_Constraints: none Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Viki Bankey Contact_Organization: U.S. Geological Survey Contact_Address: Address_Type: mailing address Address: Box 25046, MS964 Denver Federal Center City: Denver State_or_Province: CO Postal_Code: 80225-0046 Country: USA Contact_Voice_Telephone: 303-236-1348 Contact_Electronic_Mail_Address: viki@usgs.gov Data_Set_Credit: Viki Bankey (USGS) G. Randy Keller (University of Texas - El Paso) Native_Data_Set_Environment: These grids were created using the proprietary software Oasis Montaj, from Geosoft, Inc. Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: Magnetic grid values represent the total intensity of the Earth's magnetic field after removal of the International Geomagnetic Reference Field (IGRF). The data in the original grids have been processed using formulas and methods that are not usually documented but that represent industry standard practices for airborne data reduction. Logical_Consistency_Report: Survey contracts specified the conditions and specifications under which these data were collected. Standard industry practices of the time were followed in data collection and processing. Completeness_Report: Survey is complete for the area covered. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Flight Path Recovery Horizontal position of the survey aircraft used to collect data were determined using GPS satellite navigation. Vertical_Positional_Accuracy: Vertical_Positional_Accuracy_Report: The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter. Radar altimeters are estimated to have an error of 2-5 percent of the altitude (Richard Hansen, PRJ Inc., written communication). Barometric altimeters are quite accurate, but are typically operated in an uncorrected mode. The diurnal variation in air pressure over the course of a flight can produce a 50-100 ft error in the barometric altimeter reading. In addition, pressure microcells create short-period air pressure changes equivalent to about 10 ft under typical conditions (Richard Hansen, PRJ Inc., written communication) Some data were collected as a draped survey having an average terrain clearance above the ground. Because aircraft cannot safely maintain a constant terrain clearance, error in vertical position is introduced. Lineage: Process_Step: Process_Description: The creation of aeromagnetic data grid - Grids were constructed from the original aeromagnetic survey data with a cell size of between one-third and one-fifth of the flight-line spacing, using a minimum curvature gridding algorithm. For digitized contour line data, the initial grid was constructed using a minimum curvature algorithm and a spacing appropriate for the scale of the digitized map. The Definitive Geomagnetic Reference Field (DGRF) calculated for the date and elevation of the original survey was subtracted(in some cases this required the determination and removal of the original reference field). Flightlines were adjusted, and spurious anomalies (generated by equipment malfunction) were removed as necessary. The survey grids were regridded as necessary to the final grid-cell size of 1,000 m using a minimum curvature algorithm. The original survey grids were continued to 1,000 ft above ground, if necessary, and converted from level to drape as necessary. Upward continuation of the NURE surveys was by standard 2D FFT filtering techniques. The datum levels of the converted grids were adjusted (by addition or subtraction of a constant value) to minimize differences at the boundaries. These adjusted grids were combined into a single merged grid that shows the magnetic field measured or calculated at 1,000 ft (304.8 m) above ground. Weighted averaging of the data was applied in the overlap areas. Process_Date: 2004 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: raster Raster_Object_Information: Raster_Object_Type: grid cell Row_Count: 1268 Column_Count: 1364 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Map_Projection: Map_Projection_Name: Lambert Conformal Conic Lambert_Conformal_Conic: Standard_Parallel: 33.0 Standard_Parallel: 45.0 Longitude_of_Central_Meridian: -100.0 Latitude_of_Projection_Origin: 0.0 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: sphere Semi-major_Axis: 6378206.4 Denominator_of_Flattening_Ratio: 0.926 Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: This metadata file describes related gridded data with the following prefixes: texas_mag - Total-intensity magnetic data (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. Detailed_Description: Entity_Type: Entity_Type_Label: Aeromagnetic data Entity_Type_Definition: Ascii real number value Entity_Type_Definition_Source: well-established geophysical data quantity Attribute: Attribute_Label: Total-intensity magnetic data Attribute_Definition: Total-intensity magnetic data, as described in report. Attribute_Definition_Source: Nettleton, L.L., 1971, Elementary Gravity and Magnetics for geologists and seismologists: Society of Exploration Geophysicists Monograph Series No. 1. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -1370 Range_Domain_Maximum: 1638 Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Enumerated_Domain_Value_Definition_Source: program-generated Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: USGS Information Services Contact_Address: Address_Type: mailing address Address: Box 25286, Building 810 Denver Federal Center City: Denver State_or_Province: Colorado Postal_Code: 80225 Country: USA Contact_Voice_Telephone: 303-202-4700 Contact_Electronic_Mail_Address: www.usgs.gov/pubprod Resource_Description: USGS Data Series 232 Distribution_Liability: Although all data published in these grids 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. Metadata_Reference_Information: Metadata_Date: 20061201 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Viki Bankey Contact_Organization: U.S. Geological Survey Contact_Address: Address_Type: mailing address Address: U.S. Geological Survey Box 25046 Mail Stop 964 Denver Federal Center City: Denver State_or_Province: Colorado Postal_Code: 80225 Country: USA Contact_Voice_Telephone: 303-236-1348 Contact_Electronic_Mail_Address: viki@usgs.gov Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998