Identification_Information: Citation: Citation_Information: Originator: U.S. Geological Survey Publication_Date: 2009 Title: Digital data from the Great Sand Dunes and Poncha Springs aeromagnetic surveys, south-central Colorado Geospatial_Data_Presentation_Form: raster digital data Series_Information: Series_Name: U.S. Geological Survey Open-File Report Issue_Identification: Open-File Report 2009-1089 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 and survey procedures for aeromagnetic data collected during a survey covering the southern Upper Arkansas Valley, Chaffee County, October, 2008. This Poncha Springs survey covers the town of Poncha Springs and vicinity. Purpose: The overall objective of the survey is to map concealed faults that may be related to geothermal resources, such as hot springs. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 2008 Ending_Date: 2008 Currentness_Reference: data collection date Status: Progress: complete Maintenance_and_Update_Frequency: none planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -106.25 degrees W. longitude East_Bounding_Coordinate: -106.0 degrees W. longitude North_Bounding_Coordinate: 38.65 degrees N. latitude South_Bounding_Coordinate: 38.4 degrees N. latitude Keywords: Place: Place_Keyword_Thesaurus: none Place_Keyword: United States Place_Keyword: Colorado Place_Keyword: Poncha Springs Place_Keyword: Arkansas Valley 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: Tien Grauch 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: 303-236-1393 Contact_Electronic_Mail_Address: tien@usgs.gov Data_Set_Credit: V.J.S. Grauch B.J. Drenth Viki Bankey New Sense Geophysics, Ltd. 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. Grid values represent the total intensity of the Earth's magnetic field after removal of the International Geomagnetic Reference Field (IGRF). 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 employed a helicopter with an attached stinger flying along traverse lines spaced 150 m (about 500 ft) apart and oriented roughly east-west (23o–203o). Over most of the survey area, the pilot followed a pre-planned flight surface that was generally 150 m (500 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 1,500 m (4,920 ft) spacing at the same elevation as the flight lines. Total flight-line coverage was 960.5 line-kilometers. 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 - data were gridded at 50 m. - data were filtered and microlevelled as described in the report to minimise the effects of low-amplitude data noise. Process_Step: Process_Description: Creation of analytically continued, reduced-to-pole grid: The above grid was continued to a simulated flight surface of 100 m above the ground. The continued data are extrapolated from a series of parallel continuation surfaces that have each been computed using standard FFT techniques. The grid of smoothed radar-altimeter values determined the distances to upward or downward continue the data to a common terrain clearance of 100 m. 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=9.7, inclination=65.4 for the study area). 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: 50 Ordinate_Resolution: 50 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: ps84mag Total-intensity magnetic data (nT) ps84magcont Total-intensity magnetic data, analytically continued to 100 m above terrain. (nT) ps84radar Smoothed radar/laser altimeter measurements (meters) ps84rtpcont Reduced-to-the-pole magnetic data, analytically continued to 100 m above terrain. (nT) ps84topogrid Topography (meters) psmag Total-intensity magnetic data (nT) psmagcont Total-intensity magnetic data, analytically continued to 100 m above terrain. (nT) psradar Smoothed radar altimeter measurements (meters) psrtpcont Reduced-to-the-pole magnetic data, analytically continued to 100 m above terrain. (nT) Files with '84' in their names use the WGS84 datum; files without use the NAD27 datum. Detailed_Description: Entity_Type: Entity_Type_Label: Aeromagnetic and radar data Entity_Type_Definition: Ascii real number value Entity_Type_Definition_Source: well-established geophysical quantity Attribute: Attribute_Label: Total-intensity magnetic data Attribute_Definition: Total-intensity magnetic data gridded data file prefix: ps*mag, ps*magcont 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: Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Enumerated_Domain_Value_Definition_Source: program-generated Attribute: Attribute_Label: Reduced-to-the-pole magnetic data continued 100 m above ground. Attribute_Definition: Reduced-to-pole calculation used declination=9.7, inclination=65.4 for the study area. Magnetic data were analytically continued to a surface 100 m above ground as described in report. gridded data file prefix: psrtp*cont 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: Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Enumerated_Domain_Value_Definition_Source: program-generated Attribute: Attribute_Label: Radar altimeter measurements (meters) Attribute_Definition: Radar elevation measurements collected during the survey, and gridded as described in the report. Values show meters above terrain (terrain clearance). gridded data file prefix: ps*radar Attribute_Definition_Source: industry standard Attribute_Domain_Values: Enumerated_Domain: Enumerated_Domain_Value: -99999 Enumerated_Domain_Value_Definition: missing data Enumerated_Domain_Value_Definition_Source: program-generated Attribute: Attribute_Label: Topography Attribute_Definition: The topographic grid was created from 1-arc-second (30 m) digital elevation data. value in meters gridded data file prefix: ps*topogrid Attribute_Definition_Source: industry standard Attribute_Domain_Values: 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: 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 2009-1089 Distribution_Liability: The act of distribution shall not constitute any 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: 2009070 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Tien Grauch 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: 303-236-1393 Contact_Electronic_Mail_Address: tien@usgs.gov Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998