Identification_Information:
  Citation:
    Citation_Information:
      Originator: U.S. Geological Survey
      Publication_Date: 2008
      Title: Arkansas and Louisiana 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: 352
      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: 1960
        Ending_Date: 2004
    Currentness_Reference: publication date
  Status:
    Progress: complete
    Maintenance_and_Update_Frequency: none planned
  Spatial_Domain:
    Bounding_Coordinates:
      West_Bounding_Coordinate: -95.2 degrees W. longitude
      East_Bounding_Coordinate: -89.0 degrees W. longitude
      North_Bounding_Coordinate: 36.5 degrees N. latitude
      South_Bounding_Coordinate: 29.0 degrees N. latitude
  Keywords:
    Place:
      Place_Keyword_Thesaurus: none
      Place_Keyword: United States
      Place_Keyword: Arkansas
      Place_Keyword: Louisiana
    Theme:
      Theme_Keyword_Thesaurus: none
      Theme_Keyword: Bouguer gravity
      Theme_Keyword: geophysical data
      Theme_Keyword: isostatic gravity 
  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:
      Gravity grid values represent the complete-Bouguer gravity or 
      isostatic gravity measurements.
      The data in the original grids have been processed using formulas
      and methods that represent standard practices for gravity data 
      reduction.
  Logical_Consistency_Report:
    Standard industry practices of the time were followed in data 
     collection and processing.
  Completeness_Report:
    Survey is complete for the area covered as of 2007.
  Positional_Accuracy:
    Horizontal_Positional_Accuracy:
      Horizontal_Positional_Accuracy_Report: 
        Gravity station locations were primarily determined from USGS 
        topographic maps, commonly at benchmarks, section corners, road
        intersections, and similar recoverable positions, and are 
        as accurate as the maps used.
    Vertical_Positional_Accuracy:
      Vertical_Positional_Accuracy_Report:
        Gravity station elevations were primarily determined from USGS 
        topographic maps, commonly at benchmarks, section corners, road
        intersections, and similar recoverable positions, and are 
        as accurate as the contour interval of the maps used.
  Lineage:
    Process_Step:
      Process_Description: The creation of Bouguer gravity data grid -
        The complete-Bouguer gravity anomaly grid was generated from
        nearly 37,000 gravity station measurements in and adjacent to 
        the states of Arkansas and Louisiana. These data are from the
        database maintained by the National Geophysical Data Center 
        (from Department of Defense unclassified data) and augmented 
        with data from the USGS and from several university theses and 
        dissertations. Observed gravity measurements relative to the 
        IGSN-71 datum were reduced to the Bouguer anomaly using the 1967 
        gravity formula and a reduction density of 2.67 g/cc. Terrain 
        corrections were calculated radially outward from each station 
        to a distance of 167 km. The data were converted to a 2-km grid 
        using minimum curvature techniques.
      Process_Date: 2007
    Process_Step:
      Process_Description: The creation of isostatic gravity data grid -
        An isostatic residual gravity grid was derived from the Bouguer 
        gravity anomaly data by removing the gravitational effect of the 
        compensating mass that supports topographic loads. The thickness 
        of this compensating mass was calculated using averaged digital 
        topography by assuming a crustal thickness for sea level 
        topography of 30 km, a crustal density of 2.67 g/cc, and a 
        density contrast between the crust and upper mantle of 
        0.40 g/cc.
      Process_Date: 2007
Spatial_Data_Organization_Information:
  Direct_Spatial_Reference_Method: raster
  Raster_Object_Information:
    Raster_Object_Type: grid cell
    Row_Count: 435
    Column_Count: 296
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: -92.0
          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: 2
          Ordinate_Resolution: 2
        Planar_Distance_Units: kilometers
    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:
      arkla_bou - complete-Bouger gravity (mGals)
      arkla_iso - isostatic gravity (mGals).
    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: complete-Bouguer gravity data
      Entity_Type_Definition: Ascii real number value
      Entity_Type_Definition_Source: well-established geophysical data
       quantity
    Attribute:
      Attribute_Label:
        Complete-Bouguer gravity data
      Attribute_Definition:
        Complete-Bouger gravity data.
        gridded data file: arkla_bou
      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: -111.998314
          Range_Domain_Maximum: 61.402401
        Enumerated_Domain:
          Enumerated_Domain_Value: -9999
          Enumerated_Domain_Value_Definition: missing data
          Enumerated_Domain_Value_Definition_Source: program-generated
    Attribute:
      Attribute_Label:
        Isostatic gravity data.
      Attribute_Definition:
        Isostatically corrected gravity data. Assumed crustal thickness
         for sea level topography of 30 km, a crustal density of 
         2.67 g/cc, and a density contrast between the crust and upper 
         mantle of 0.40 g/cc.
        gridded data file prefix: arkla_iso
      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: -82.4788472
          Range_Domain_Maximum: 53.8332406
        Enumerated_Domain:
          Enumerated_Domain_Value: -9999
          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 352
  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