Identification_Information: Citation: Citation_Information: Originator: B.J. Drenth Originator: J.D. Abraham Originator: V.J.S. Grauch Originator: V.F. Labson Originator: G. Hodges Publication_Date: 2013 Title: Digital data from the Great Sand Dunes Airborne Gravity Gradient Survey, South-Central Colorado Geospatial_Data_Presentation_Form: raster digital data Series_Information: Series_Name: Open-File Report Issue_Identification: 2013-1011 Publication_Information: Publication_Place: Denver, Colo., USA Publisher: U.S. Geological Survey Description: Abstract: This report contains digital data and supporting explanatory files describing data types, data formats, and survey procedures for a high-resolution airborne gravity gradient (AGG) survey at Great Sand Dunes National Park, Alamosa and Saguache Counties, south-central Colorado. In the San Luis Valley, the Great Sand Dunes survey covers a large part of Great Sand Dunes National Park and Preserve. 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 to understand groundwater systems in populated alluvial basins along the Rio Grande rift. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 2012 Ending_Date: 2012 Currentness_Reference: data collection date Status: Progress: complete Maintenance_and_Update_Frequency: none planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -105.8 degrees W. longitude East_Bounding_Coordinate: -105.5 degrees W. longitude North_Bounding_Coordinate: 37.9 degrees N. latitude South_Bounding_Coordinate: 37.5 degrees N. latitude Keywords: Place: Place_Keyword_Thesaurus: none Place_Keyword: United States Place_Keyword: Colorado Place_Keyword: Great Sand Dunes National Park Place_Keyword: San Luis basin Theme: Theme_Keyword_Thesaurus: none Theme_Keyword: airborne gravity gradient data Theme_Keyword: geophysical data Theme_Keyword: airborne gravity gradient grid Access_Constraints: none Use_Constraints: none Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Benjamin Drenth 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: 303-236-1827 Contact_Electronic_Mail_Address: bdrenth@usgs.gov Data_Set_Credit: B.J. Drenth J.D. Abraham V.J.S. Grauch V.F. Labson G. Hodges Fugro Airborne Surveys Corp. 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 gradient values represent the full tensor gradient representation of the Earth's gravitational field. 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 was 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) 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: Flight data processing: The survey was flown in two separate, partially overlapping blocks. In area 1, the survey employed a helicopter with an internal sensor flying along traverse lines spaced 100 m (about 328 ft) apart and oriented roughly east-west (90–270 degrees). Over most of the survey area, the pilot followed a pre-planned flight surface that was generally 80 m (262 ft) above ground. The aircraft smoothly increased in flight height, subject to safety precautions, to equalize rates of climb and descent over high topography. Orthogonal tie lines were flown roughly north-south at a 1000 m (3,280 ft) spacing at the same elevation as the flight lines. In area 2, the survey employed a helicopter with an internal sensor flying along traverse lines spaced 50 m (about 164 ft) apart and oriented roughly east-west (90–270 degrees). Over most of the survey area, the pilot followed a preplanned flight surface that was generally 40 m (131 ft) above ground. The aircraft smoothly increased in flight height, subject to safety precautions, to equalize rates of climb and descent over high topography. Orthogonal tie lines were flown roughly north-south at a 500 m (1,640 ft) spacing at the same elevation as the flight lines. Total flight-line coverage was 2001 line-kilometers. Process_Date: 2012 Process_Step: Process_Description: Creation of AGG data grids: AGG data were processed so that residual values were calculated in a consistent manner, as described in the report and Appendix 1. Process_Date: 2012 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: raster Raster_Object_Information: Raster_Object_Type: grid cell Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Map_Projection: Map_Projection_Name: Universal Transverse Mercator Transverse_Mercator: Scale_Factor_at_Central_Meridian: 0.9996 Longitude_of_Central_Meridian: -105.0 Latitude_of_Projection_Origin: 0.0 False_Easting: 500,000 m False_Northing: 0 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: row and column Coordinate_Representation: Abscissa_Resolution: 25, 12.5, and 100 (grid dependent) Ordinate_Resolution: 25, 12.5, and 100 (grid dependent) Planar_Distance_Units: meters Geodetic_Model: Horizontal_Datum_Name: NAD 1983 Ellipsoid_Name: GRS 1980 Semi-major_Axis: 6378137 Denominator_of_Flattening_Ratio: 298.25722 Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: This metadata file describes related gridded data with the following prefixes: area1_Gdd_fourier_0p00 Gdd with no terrain correction (Eo) area1_Gdd_fourier_2p67 Gdd, terrain corrected using 2.67 g/cc density (Eo) area2_Gdd_fourier_0p00 Gdd with no terrain correction (Eo) area2_Gdd_fourier_2p67 Gdd, terrain corrected using 2.67 g/cc density (Eo) conformed_gravity_2p67 Airborne gravity field, conformed with ground data (mGal) Entity_and_Attribute_Detail_Citation: Sheriff, R.E., 2002, Encyclopedic Dictionary of Applied Geophysics, 4th Ed.: Society of Exploration Geophysicists, 429 p. Detailed_Description: Entity_Type: Entity_Type_Label: gravity gradient and gravity data Entity_Type_Definition: Ascii real number value Entity_Type_Definition_Source: well-established geophysical quantity Attribute: Attribute_Label: gravity data Attribute_Definition: gravity gradient tensor and gravity data Attribute_Definition_Source: producer defined Attribute_Domain_Values: Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Enumerated_Domain_Value_Definition_Source: none Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Address: Address_Type: mailing address Address: Box 25286, Building 810 Denver Federal Center City: Denver State_or_Province: CO Postal_Code: 80225 Country: USA Contact_Voice_Telephone: 1-888-ASK-USGS Contact_Electronic_Mail_Address: answers.usgs.gov Resource_Description: USGS Open-File Report 2013-1011 Distribution_Liability: This database, identified as OFR 2013-1011, has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also contains copyrighted materials as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. Metadata_Reference_Information: Metadata_Date: 201208 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Benjamin Drenth 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: CO Postal_Code: 80225 Country: USA Contact_Voice_Telephone: 303-236-1827 Contact_Electronic_Mail_Address: bdrenth@usgs.gov Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998