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Isostatic residual gravity anomaly data grid for the conterminous US

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: Robert P. Kucks

Publication_Date: 1999

Title:

Isostatic residual gravity anomaly data grid for the conterminous US

Online_Linkage:

<http://mrdata.usgs.gov/services/gravity?request=getcapabilities&service=WMS&version=1.1.1>&

Larger_Work_Citation:

Citation_Information:

Originator: U.S. Geological Survey

Title:

National geophysical data grids; gamma-ray, gravity, magnetic and topographic data for the conterminous United States

Publication_Date: 1993

Series_Information:

Series_Name: U.S. Geological Survey Digital Data Series

Issue_Identification: DDS-9

Description:

Abstract:

The grid of isostatic residual gravity anomaly data was produced from the grid of Bouguer gravity anomaly data (see Bouguer gravity metadata) by using an Airy-Heiskanen compensation model with three parameters. The depth to the compensating root at sea level was chosen to be 30 km. The density contrast across the root was chosen to be 0.35 grams per cubic centimeter, and the the density of the topography was chosen to be 2.67 grams per cubic centimeter.

Supplemental_Information:

Digital Data Series DDS-9 (CD-ROM) contains gridded geophysical data (isostatic gravity anomaly data only defined here) images generated from the data, software for displaying and analyzing the images, software for processing potential-field geophysical data, and documentation files that describe the data and software.

Purpose:

Isostatic residual gravity anomaly maps are produced by subtracting long-wavelength anomalies produced by masses deep within the crust or mantle from the Bouguer anomaly map. The long-wavelength anomalies are assumed to result from isostatic compensation of topographic loads. Isostatic residual gravity anomaly maps therefore reveal more clearly than Bouguer gravity anomaly maps the density distributions within the upper crust that are of interest in many geologic and tectonic studies.

Time_Period_of_Content:

Time_Period_Information:

Range_of_Dates/Times:

Beginning_Date: 1998

Ending_Date: 1999

Currentness_Reference: reprocessing for SDD website

Status:

Progress: Complete

Maintenance_and_Update_Frequency: None planned

Spatial_Domain:

Bounding_Coordinates:

West_Bounding_Coordinate: -125

East_Bounding_Coordinate: -65

North_Bounding_Coordinate: 49

South_Bounding_Coordinate: 25

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:

Box 25046, MS 964
Denver Federal 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

Data_Set_Credit:

The compilation of onshore data consisted of nearly one million Bouguer gravity anomaly values computed by using a reduction density of 2.67 grams per cubic centimeter. The offshore data consisted of approximately 800,000 free-air gravity anomaly values. The isostatic calculation was produced from these data

USGS employees: Simpson and Jachens

Native_Data_Set_Environment:

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

Keywords:

Theme:

Theme_Keyword_Thesaurus: none

Theme_Keyword: gravity, Bouguer, isostatic

Theme:

Theme_Keyword_Thesaurus: ISO 19115 Topic Categories

Theme_Keyword: geoscientificInformation

Place:

Place_Keyword_Thesaurus: none

Place_Keyword: United States

Data_Quality_Information:

Attribute_Accuracy:

Attribute_Accuracy_Report:

Initially the accuracy of the gravity anomaly value for each station is critical. Choices of the parameters used to calculate isostatic gravity are dependent on the geologic and tectonic setting and are subject to the discretion of the person carrying out the calculations.

Gravity measurements made on the surface of the Earth must be corrected in various way before they can be made into an anomaly map. The free-air correction reduces the measurement to sea level by assuming there is no intervening mass as a uniform slab of constant density, and the complete Bouguer correction includes the effects of constant density topography within 166.7 km of the measurement location. A gravity reference field is subtracted from the corrected measurements to produce the free-air, simple Bouguer, or complete Bouguer anomaly. The data set constitutes many years of individual collection of gravity stations and therefore is difficult to access the precise accuracy.

Quantitative_Attribute_Accuracy_Assessment:

Attribute_Accuracy_Value: overall station accuracy of less than 2 milligals

Positional_Accuracy:

Horizontal_Positional_Accuracy:

Horizontal_Positional_Accuracy_Report:

Earlier collection of stations was by surveying methods. Positions were also acquired from locations on topographic maps. Recently the station latitudes, longitudes and elevations were acquired by Geopositioning Satellite (GPS) systems.

Quantitative_Horizontal_Positional_Accuracy_Assessment:

Horizontal_Positional_Accuracy_Value: 100

Horizontal_Positional_Accuracy_Explanation:

surveying methods - 1.0 meter topographic maps - 3.0 meter GPS systems - 100.0 meter/1.0 meter differential

Vertical_Positional_Accuracy:

Vertical_Positional_Accuracy_Report: see Horizontal_Positional_Accuracy_Report

Quantitative_Vertical_Positional_Accuracy_Assessment:

Vertical_Positional_Accuracy_Value: 100

Vertical_Positional_Accuracy_Explanation:

surveying methods - 1.0 meter topographic maps - 1.0-20.0 meter GPS systems - 100 meter/1.0 meter differential

Lineage:

Process_Step:

Process_Description:

Isostatic residual gravity anomaly grid was extracted from DDS-9 and reprojected using USGS in-house developed software. In-house software was also used to convert from USGS grid format to Arc-Info grid format.

Source_Used_Citation_Abbreviation:

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

Process_Date: 1999

Process_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Robert P. Kucks

Contact_Organization: U.S. Geological Survey

Contact_Address:

Address:

Box 25046, MS 964
Denver Federal Center

City: Denver

State_or_Province: CO

Postal_Code: 80225-0046

Country: USA

Address_Type: mailing address

Contact_Electronic_Mail_Address: rkucks@usgs.gov

Contact_Voice_Telephone: (303)236-1405

Logical_Consistency_Report:

The accuracy of the data set that generated the grid is totally dependant on the individual who collected each gravity station. In the case of a national set they would number in the hundreds. Variations would include latitude, longitude, elevation, raw gravity reading and base station control.

Completeness_Report:

There will always be upgrades and additions to the data set that generated the grid due to regional interests.

Spatial_Data_Organization_Information:

Direct_Spatial_Reference_Method: Raster

Raster_Object_Information:

Raster_Object_Type: Grid cell

Row_Count: 768

Column_Count: 1300

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:

Planar:

Map_Projection:

Albers_Conical_Equal_Area:

Standard_Parallel: 29.5

Standard_Parallel: 45.5

Longitude_of_Central_Meridian: -96.0

Latitude_of_Projection_Origin: 37.5

False_Easting: 0.

False_Northing: 0.

Map_Projection_Name: Albers Conical Equal Area

Planar_Coordinate_Information:

Planar_Coordinate_Encoding_Method: row and column

Coordinate_Representation:

Abscissa_Resolution: 4.0

Ordinate_Resolution: 4.0

Planar_Distance_Units: kilometer

Geodetic_Model:

Horizontal_Datum_Name: Noth American Datum of 1927

Ellipsoid_Name: CLARKE1866

Semi-major_Axis: 6378.20640

Denominator_of_Flattening_Ratio: 0.99661

Entity_and_Attribute_Information:

Detailed_Description:

Entity_Type:

Entity_Type_Label: grid cell

Entity_Type_Definition: Area of Earth's surface for which gravity anomaly is summarized

Attribute:

Attribute_Label: cell value

Attribute_Definition:

Value, in milligals, of the gravity anomaly of Earth's gravitational field.

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: -225

Range_Domain_Maximum: 105

Attribute_Units_of_Measure: milligal

Attribute_Measurement_Resolution: 0.1

Attribute_Domain_Values:

Enumerated_Domain:

Enumerated_Domain_Value: -0.3402823E+39

Enumerated_Domain_Value_Definition: areas for which no data are available in the grid

Distribution_Information:

Distributor:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Robert P. Kucks

Contact_Organization: U.S. Geological Survey

Contact_Address:

Address_Type: mailing address

Address:

Box 25046, MS 964
Denver Federal Center

City: Denver

State_or_Province: CO

Postal_Code: 80225

Country: USA

Contact_Voice_Telephone: (303)236-1405

Contact_Electronic_Mail_Address: rkucks@usgs.gov

Resource_Description: USGS Digital Data Series DDS-9

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: ArcInfo export

Format_Version_Number: 7.x

Format_Specification: Arc-Info grid format

Format_Information_Content: Gridded gravity anomaly data

File_Decompression_Technique: gunzip

Transfer_Size: 3.5 megabytes

Digital_Transfer_Option:

Online_Option:

Computer_Contact_Information:

Network_Address:

Network_Resource_Name:

<ftp://ftpext.usgs.gov/pub/cr/co/denver/musette/pub/GEOPHYSICAL_DATA/cdrom_DDS-9/GRIDS/ARC_INFO/isograv_sdd.e00.gz>

Digital_Form:

Digital_Transfer_Information:

Format_Name: OGC WMS

Format_Version_Number: 1.1.1

Format_Information_Content: Isostatic gravity anomaly

Digital_Transfer_Option:

Online_Option:

Computer_Contact_Information:

Network_Address:

Network_Resource_Name:

<http://mrdata.usgs.gov/services/gravity?request=getcapabilities&service=WMS&version=1.1.1>&

Fees: none

Metadata_Reference_Information:

Metadata_Date: 20091118

Metadata_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Robert P. Kucks

Contact_Organization: U.S. Geological Survey

Contact_Address:

Address_Type: mailing address

Address:

Box 25046, MS 964
Denver Federal Center

City: Denver

State_or_Province: CO

Postal_Code: 80225

Country: USA

Contact_Voice_Telephone: (303)236-1405

Contact_Electronic_Mail_Address: rkucks@usgs.gov

Metadata_Standard_Name: Content Standard for Digital Geospatial Metadata

Metadata_Standard_Version: FGDC-STD-001-1998