Identification_Information: Citation: Citation_Information: Originator: U.S. Geological Survey Publication_Date: June 2005 Title: Digital data and derivative products from a high-resolution aeromagnetic survey of the central San Luis basin, covering parts of Alamosa, Conejos, Costilla, and Rio Grande Counties, Colorado, and Taos County, New Mexico Geospatial_Data_Presentation_Form: raster digital data Series_Information: Series_Name: U.S. Geological Survey Open-File Report Issue_Identification: Open-File Report 2005-1200 Publication_Information: Publication_Place: Denver, Colorado, USA Publisher: U.S. Geological Survey Other_Citation_Details: This citation refers to the CD and USGS web site that presents the digital gridded data from an aeromagnetic survey of the central San Luis basin, Colorado and New Mexico Description: Abstract: This report contains digital data, image files, and text files describing data formats and survey procedures for aeromagnetic data collected during a high-resolution aeromagnetic survey in southern Colorado and northern New Mexico during October, 2004. The survey covers the central San Luis basin in Alamosa, Conejos, Costilla, and Rio Grande Counties, Colorado, and Taos County, New Mexico. 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 ground-water systems in populated alluvial basins along the Rio Grande. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 2004 Ending_Date: 2004 Status: Progress: complete Maintenance_and_Update_Frequency: none planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -106.25 degrees W. longitude East_Bounding_Coordinate: -105.5 degrees W. longitude North_Bounding_Coordinate: 37.5 degrees N. latitude South_Bounding_Coordinate: 36.5 degrees N. latitude Keywords: Place: Place_Keyword_Thesaurus: none Place_Keyword: United States Place_Keyword: New Mexico Place_Keyword: Colorado Place_Keyword: San Luis 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) V.J.S. Grauch A. Webbers PRJ, Inc. 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: 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% 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 aeromagnetic survey for the area employed a fixed-wing aircraft flying along traverse lines oriented east-west, spaced 200 m (about 650 ft) apart, and flown a nominal 150 m (500 ft) above ground. Orthogonal lines were flown north-south at a 1000-m (3280 ft) spacing. Total line-kilometers flown was 2,522 line kilometers (1,567 line miles). Process_Step: Process_Description: Creation of aeromagnetic data grid: Aeromagnetic data were processed so that residual magnetic values were calculated in a consistent manner: - The DGRF, updated to survey date, was removed - The flight elevation was used to mathematically calculate the equivalent magnetic field at 100 ft. above terrain - data were gridded at 50 m. Process_Step: Process_Description: Creation of reduced-to-the-pole grid: The reduction-to-pole (RTP) transformation corrects for the offset between the locations of anomalies (closed highs or lows on a contour map) and their sources that is a consequence of the vector nature of the Earth's magnetic field. To apply the reduced-to-pole transformation, one must assume that the total magnetizations of most rocks in the study area align parallel or anti-parallel to the Earth's main field (declination=10o, inclination=64o for the study area). Process_Step: Process_Description: The RTP magnetic grid was downward continued to a reference surface 100 m above ground, using the chessboard method of Cordell and Grauch (1985). In the chessboard method, the continued data are extrapolated from a series of parallel continuation surfaces that each have been computed using standard Fast Fourier transform (FFT) techniques. The radar-altimeter channel was used to create the terrain clearance grid, which, in turn, determined the distances to continue the data. Radar-altimeter data from the contractor were leveled using the tie-line data to better approximate the flight surface. Downward continuation significantly enhances details in aeromagnetic maps, but also amplifies noise. Process_Step: Process_Description: First vertical derivative of the downward-continued RTP data was calculated. To minimize amplification of noise during the operation, a Butterworth filter with a cutoff wavelength of 200 m was applied. Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: raster Raster_Object_Information: Raster_Object_Type: grid cell Row_Count: 306 Column_Count: 533 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: 50 Ordinate_Resolution: 50 Planar_Distance_Units: meters Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1927 Ellipsoid_Name: sphere Semi-major_Axis: 6371204.0 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: cslmaggrd.gxf Levelled total-intensity magnetic data (nanoTeslas - nT) cslrtpgrd.gxf Reduced-to-the-pole, total-intensity magnetic data (nT) cslrdrgrd.gxf Leveled radar altimeter measurements (meters) cslrtpcontgrd.gxf Filtered, reduced-to-the-pole, total-intensity magnetic data (nT) cslrtpcont1stvergrd.gxf First vertical derivative of filtered, reduced-to-the-pole, total-intensity magnetic data cslcontsurfgrd.gxf continuation surface (meters) csltopomgrd.gxf topography (meters) Detailed_Description: Entity_Type: Entity_Type_Label: Levelled total-intensity magnetic data (nanoTeslas - nT) Entity_Type_Definition: Ascii real number value Entity_Type_Definition_Source: well-established geophysical data quantity Attribute: Attribute_Label: Residual total intensity of Earth's magnetic field Attribute_Definition: The total magnetic value minus a geomagnetic reference field (GRF), which is a long-wavelength regional magnetic field. gridded data file prefix: cslmaggrd Attribute_Definition_Source: see: Nettleton, L.L., 1971, Elementary Gravity and Magnetics for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series No. 1, p. 83-87. A description of magnetometers and how they measure the total magnetic field can be found in: Dobrin, M.B., 1976, Introduction to Geophysical Prospecting: New York, McGraw-Hill Book Company, p. 505-517. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -2295.613 Range_Domain_Maximum: 1999.581 Attribute_Units_of_Measure: nanoteslas Attribute_Measurement_Resolution: 1-10 nanoteslas Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 1 nanoteslas Attribute_Value_Accuracy_Explanation: The Geomagnetic Reference Field that was subtracted from the total magnetic value is based on a model, which was updated to the date of the survey. Attribute: Attribute_Label: Reduced-to-the-pole, total-intensity magnetic data Attribute_Definition: The reduction-to-pole (RTP) transformation corrects for the offset between the locations of anomalies (closed highs or lows on a contour map) and their sources that is a consequence of the vector nature of the Earth's magnetic field. To apply the reduced-to-pole transformation, one must assume that the total magnetizations of most rocks in the study area align parallel or anti-parallel to the Earth's main field (declination=10o, inclination=64o for the study area). gridded data file prefix: cslrtpgrd Attribute_Definition_Source: Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -2677.275 Range_Domain_Maximum: 1484.486 Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Attribute: Attribute_Label: Leveled radar altimeter measurements (meters) Attribute_Definition: Radar elevation measurements collected during the survey, and processed using tie-line radar information to approximate a more consistant, levelled grid. Values show meters above terrain (terrain clearance) gridded data file prefix: cslrdrgrd Attribute_Definition_Source: industry standard Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 40.03073 Range_Domain_Maximum: 1179.671 Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Attribute: Attribute_Label: Filtered, reduced-to-the-pole, total-intensity magnetic data (nT) Attribute_Definition: The RTP magnetic grid was downward continued to a reference surface 100 m above ground, using the chessboard method of Cordell and Grauch. In the chessboard method, the continued data are extrapolated from a series of parallel continuation surfaces that each have been computed using standard Fast Fourier transform (FFT) techniques. The radar-altimeter channel was used to create the terrain clearance grid, which, in turn, determined the distances to continue the data. gridded data file prefix: cslrtpcontgrd Attribute_Definition_Source: Cordell and Grauch, 1985, Mapping basement magnetization zones from aeromagnetic data in the San Juan Basin, New Mexico, in Hinze, W.J., ed., The Utility of Regional Gravity and Magnetic Anomaly Maps: Society of Exploration Geophysicists: Tulsa, Oklahoma, p. 181-197. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -2574.636 Range_Domain_Maximum: 1783.423 Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Attribute: Attribute_Label: First vertical derivative of the filtered, reduced-to-the-pole, total-intensity magnetic data (nT) Attribute_Definition: The first vertical derivative was calculated from the RTP, downward-continued grid. gridded data file prefix: cslrtpcont1stvergrd Attribute_Definition_Source: industry standard Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -20.85597 Range_Domain_Maximum: 16.60756 Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: CD distributor: USGS Information Services 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: 303-202-4700 Contact_Electronic_Mail_Address: www.usgs.gov/pubprod Resource_Description: USGS Open-File Report OFR 2005-1200 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: 20050527 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: CO 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