Identification_Information: Citation: Citation_Information: Originator: U.S. Geological Survey, Department of Interior and the National Geophysical Data Center, NOAA Publication_Date: 2001 Title: Virgin Valley, Nevada Geospatial_Data_Presentation_Form: tabular digital data Larger_Work_Citation: Citation_Information: Originator: U.S. Geological Survey, Department of the Interior, and the National Geophysical Data Center Publication_Date: 2001 Title: Digital flight-line aeromagnetic data sets of the Conterminous United States, Hawaii, and Puerto Rico Series_Information: Series_Name: U.S. Geological Survey Open-File Report Issue_Identification: OFR 02-0361 Publication_Information: Publication_Place: Denver, CO Publisher: U.S. Geological Survey Description: Abstract: Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. This dataset presents latitude, longitude, altitude, and magnetic-field values. Purpose: Aeromagnetic surveys are used for geophysical prospecting. Some variations in magnetic measurements are caused by rocks that contain significant amounts of magnetic minerals (magnetite being the most common). These anomalies reflect variations in the amount and type of magnetic material and the shape and depth of the body of rock. Aeromagnetic anomaly maps are important tools in mapping surficial and buried igneous rocks. The features and patterns of aeromagnetic anomalies can also be used to delineate details of subsurface geology including the locations of buried faults and the thickness of surficial sedimentary rocks. Supplemental_Information: The U.S. Geological Survey has contracted or flown numerous airborne surveys over a long period (1950's to present). Not all flight-line data have been released to the public because of lack of personnel to reformat data and service the requests. With the improvement in digital communication and the ability to store and transmit large data sets, the USGS is now able to release the flight-line data in a common format. A companion CD-ROM/web site has been released containing magnetic data that were generated by digitizing analog maps. Digital flight-line data used to create the analog maps are unavailable. Reference is in the Cross-Reference section of this metadata file. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 199709 Ending_Date: 199709 Currentness_Reference: Time period indicates dates of airborne survey data collection. Time period is expressed in the format YYYYMM or YYYYMMDD when further accuracy is available. Status: Progress: complete Maintenance_and_Update_Frequency: none planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -114.41 East_Bounding_Coordinate: -114.00 North_Bounding_Coordinate: 37.29 South_Bounding_Coordinate: 36.62 Data_Set_G-Polygon: Data_Set_G-Polygon_Outer_G-Ring: G-Ring: -114.24 37.29, -114.00 37.29, -114.00 36.73, -114.28 36.64, -114.29 37.00, -114.34 37.00, -114.41 37.14, -114.24 37.29 Keywords: Theme: Theme_Keyword_Thesaurus: none Theme_Keyword: geophysical surveys Theme_Keyword: aeromagnetic data Theme_Keyword: airborne surveys Theme_Keyword: magnetic surveys Theme_Keyword: residual magnetic field Theme_Keyword: total field Theme_Keyword: magnetic Place: Place_Keyword_Thesaurus: none Place_Keyword: United States Place_Keyword: Nevada Place_Keyword: NV Place_Keyword: Virgin Valley Place_Keyword: Tule Desert Place_Keyword: Meadow Valley Wash Access_Constraints: none Use_Constraints: none. Acknowledgement of the U.S. Geological Survey and the National Geophysical Data Center would be appreciated in products derived from these data. Point_of_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: USGS Gravity and Magnetics Contact 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 Contact_Voice_Telephone: 303-236-1343 Contact_Electronic_Mail_Address: grav_mag@usgs.gov Browse_Graphic: Browse_Graphic_File_Name: http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-02-0361 Browse_Graphic_File_Description: An image of the flight lines showing total magnetic intensity along the flight lines. Browse_Graphic_File_Type: JPEG Data_Set_Credit: These USGS employees contributed to reformatting and archiving these data: Viki Bankey, Carol Finn, Pat Hill, Holly Hindle, Bob Kucks, Vicki Rystrom, Sarah Shearer Cooperating contributors from the National Geophysical Data Center are: Ronald Buhmann, David Dater, Susan McLean, Stewart Racey Native_Data_Set_Environment: These data were originally recorded on 9-track magnetic tapes and were transferred to CD-ROM. Data processing took place on an HP workstation running a Windows NT operating system. Data were reformatted using the Geosoft, Inc., program Oasis Montaj version 4.3. Cross_Reference: Citation_Information: Originator: U.S. Geological Survey Publication_Date: 1999 Title: Digitized Aeromagnetic Datasets of the Conterminous United States, Hawaii, and Puerto Rico Geospatial_Data_Presentation_Form: raster digital data Series_Information: Series_Name: U.S. Geological Survey Open-File Report Issue_Identification: OFR 99-557 Publication_Information: Publication_Place: Denver CO Publisher: U.S. Geological Survey Other_Citation_Details: CD-ROM or online files Complements this publication with analog data Online_Linkage: http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-99-0557 Cross_Reference: Citation_Information: Originator: U.S. Geological Survey Publication_Date: 1998 Title: Interpretation of an aeromagnetic survey over part of the Virgin Valley, Tule Desert, and the valley surrounding Meadow Valley Wash, southeastern Nevada, OFR 98-0804 Geospatial_Data_Presentation_Form: map Series_Information: Series_Name: U.S. Geological Survey Open-File Report Issue_Identification: OFR 98-0804 Publication_Information: Publication_Place: Denver, CO Publisher: U.S. Geological Survey Other_Citation_Details: Jachens, R.C., Dixon, G.L., Langenheim, V.E., and Morin, R.L. 14 pages, 1 sheet map scale 1:250,000 Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: The data in this file have been processed using various formulas and methods that are not usually documented but that represent industry standard practices for airborne data reduction. For example, position is listed as latitude and longitude, but these values were derived from the raw navigation data depending on the system used. (see notes under horizontal accuracy). Line numbers were added to records, and unusable data at flight-line ends were discarded (as aircraft slowed and turned around). Separate recordings were correlated by time and assigned to the correct location. The exact accuracies of these processing steps may not be known. They are discussed in the sections on attribute or positional accuracies. Logical_Consistency_Report: The data in this file were collected by a single contractor or group who were responsible for collecting and processing the data. The data from this survey were collected using the same instruments (magnetometers, altimeters, navigational systems) throughout the survey and were collected in a normal length of time with no long delays between survey beginning and end. 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: Loss of data due to poor transmission, channel dropout, obvious spiking, missing channels, and other obvious errors were replaced with the value -9999.9. For line 1140, the original contractor day was defined as 330. Based on the date of the surrounding lines in the survey, it was reset as 303. In order to conform to the established template and maintain the distinction between various parts of a line, lines originally ending in .1 were renumbered to a whole integer (e.g. line 100.1 was renumbered line 101). 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) The magnetometer was carried in a bird towed on a line that was approximately 50 feet below the aircraft. The bird as it is towed is slightly behind the aircraft and therefore the vertical distance between the magnetometer and the aircraft is slightly less than the length of the line but remains constant for the survey. This data set was collected at a draped survey having a average terrain clearance of 500 ft. Because aircraft, especially airplanes, cannot safely maintain a constant terrain clearance, error in vertical position is introduced. Lineage: Process_Step: Process_Description: Conversion of measured values to geographic position and magnetic values was performed by the contractor using industry standard practices. Details are found under Attribute Accuracy Report, Horizontal_Position_Accuracy_Report, and Vertical_Position_Accuracy_Report Unless noted, conversion processes were not reported to the USGS. Unpublished products generated by the contractor included magnetic tapes, a map of residual or total field magnetics, and perhaps some written documentation. Process_Date: 1998 Process_Step: Process_Description: USGS reformatting of contractor data to standard format. USGS personnel used the software package Oasis Montaj version 4.3 by Geosoft, Inc., to read in the original contractor's data. Latitude, longitude, altitude, and magnetic values were checked for obvious errors or spikes and values of -9999.9 were given where the value could not be reasonably corrected. Other errors in the data were not corrected. Horizontal positions were converted to latitude and longitude if the original values were UTM meters. Elevations were converted from meters to feet (1 m = 3.2808 ft). Information was added that was missing from the data file but was recorded elsewhere. The reformatted data file was written in the format described in the section on Entity_and_Attribute_Overview. Process_Date: 200208 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: point Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: .0001 Longitude_Resolution: .0001 Geographic_Coordinate_Units: decimal degrees Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1927 Ellipsoid_Name: Clarke 1866 Semi-major_Axis: 6,378,206.4 Denominator_of_Flattening_Ratio: 294.98 Vertical_Coordinate_System_Definition: Altitude_System_Definition: Altitude_Datum_Name: National Geodetic Vertical Datum of 1929 Altitude_Resolution: 1 Altitude_Distance_Units: feet Altitude_Encoding_Method: Explicit elevation coordinate included with horizontal coordinates Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: Airborne survey specifications These items are constant for the entire survey Project number: 4203 Project name: Virgin Valley, Nevada Survey flown by: TransNorthern Aviation Survey processed by: PRJ Survey compiled by: Aero Surveys Survey flown for: U.S. Geological Survey Approx. no. of line miles: 3210 Survey height: 500 ft Altitude method: Draped over terrain Flight-line spacing: 0.25 mi Flight-line direction: N47E Aircraft used: Cessna 180 or Cessna 185 Airport - arrival: Mesquite, NV or St. George, UT Airport - departure: Mesquite, NV or St. George, UT Magnetometer used: Geometrics G-822A or Scintrex CS-2 Sensor tow distance: 50 ft 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, p. 83-87. Dobrin, M.B., 1976, Introduction to Geophysical Prospecting: New York, McGraw-Hill Book Company, p. 505-517. Overview_Description: Entity_and_Attribute_Overview: Each record contains the following 11 attributes: No abbrev.name contents 1 line_no flight line number 2 directn flight line direction, azimuth degrees from north (integer) 3 longitud longitude (decimal degrees) 4 latitude latitude (decimal degrees) 5 year year flown (integer) 6 jul_day Julian day flown (integer) 7 fiducial fiducial number (integer) 8 radar radar altimeter reading above ground (feet) 9 barom altitude above mean sea level (feet) 10 totmag corrected magnetic value (nT) 11 resmag residual magnetic value (nT) 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, p. 83-87. Dobrin, M.B., 1976, Introduction to Geophysical Prospecting: New York, McGraw-Hill Book Company, p. 505-517. Detailed_Description: Entity_Type: Entity_Type_Label: record for one magnetic data point Entity_Type_Definition: The set of all measurements reported for a magnetic data point having the same spatial location. Entity_Type_Definition_Source: Standard aeromagnetic data collection procedures as written in the contract for survey collection. Attribute: Attribute_Label: line_no Attribute_Definition: flight line number Attribute_Definition_Source: often assigned by airborne survey crew Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 1 Range_Domain_Maximum: 9050 Attribute_Units_of_Measure: alphanumeric value Attribute: Attribute_Label: directn Attribute_Definition: direction of flight line, azimuth degrees clockwise from north Attribute_Definition_Source: self evident Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 0 Range_Domain_Maximum: 270 Attribute_Units_of_Measure: degrees Attribute: Attribute_Label: longitud Attribute_Definition: longitude - geographic coordinate Attribute_Definition_Source: self evident Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -114.4346 Range_Domain_Maximum: -113.9884 Attribute_Units_of_Measure: decimal degrees Attribute: Attribute_Label: latitude Attribute_Definition: latitude - geographic coordinate Attribute_Definition_Source: self evident Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 36.6252 Range_Domain_Maximum: 37.2985 Attribute_Units_of_Measure: decimal degrees Attribute: Attribute_Label: year Attribute_Definition: year of data point collection Attribute_Definition_Source: self evident Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 1997 Range_Domain_Maximum: 1998 Attribute: Attribute_Label: jul_day Attribute_Definition: Julian day, where Jan. 1 = 1 and Dec. 31 = 365 or 366 (leap year) Attribute_Definition_Source: self evident Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 304 Range_Domain_Maximum: 131 Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 31 Attribute_Value_Accuracy_Explanation: Both beginning and end julian dates were taken from dataset. Since this survey was flown into the next year (1997 and 1998) the minimum jul_day is 304 and the maximum jul_day is 131, based on calendar days. Attribute: Attribute_Label: fiducial Attribute_Definition: A fiducial number is a mark which indicates points of simultaneity. It is a user-defined integer used during airborne operations to correlate recording devices (magnetometers) with navigational records (altimeters, camera film, strip charts) that were recorded at the same time. Attribute_Definition_Source: Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists, p. 89. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 290 Range_Domain_Maximum: 103740 Attribute: Attribute_Label: radar Attribute_Definition: radar altimetry reading, in feet An aircraft navigational system in which short electromagnetic waves are transmitted, and the energy scattered back by reflection is detected. From this measurement, the distance between the aircraft and the ground is calculated and recorded as radar altimetry. Values of -9999.9 indicate missing data. Attribute_Definition_Source: Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists, p. 89. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 13.1 Range_Domain_Maximum: 4537.3 Attribute_Units_of_Measure: feet Attribute: Attribute_Label: barom Attribute_Definition: altitude above mean sea level, in feet, measured using the barometer that is part of the aircraft navigation system Values of -9999.9 indicate missing data. Attribute_Definition_Source: self evident Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 1601.0 Range_Domain_Maximum: 5725 Attribute_Units_of_Measure: feet Attribute: Attribute_Label: totmag Attribute_Definition: Raw magnetic value with base magnetometer corrections applied. Because the magnetic field of the earth varies diurnally, a stationary base magnetometer is maintained on the ground during airborne surveying. The base magnetometer records changes in the magnetic field (in nanoTeslas) as a function of time. The magnetic changes may have an amplitude of 20 to 50 nanoTeslas. If changes are more severe, as would occur from a magnetic storm, surveying is discontinued or the data recorded are not used. Diurnal variations are then removed from the airborne magnetic data based on the common time. Values of -9999.9 indicate missing data. 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: 50518.84 Range_Domain_Maximum: 51529.45 Attribute_Units_of_Measure: nanoTeslas Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 2 Attribute_Value_Accuracy_Explanation: The airborne magnetometer is accurate to about 1 nanoTesla, and the base magnetometer has the same accuracy. The accuracy of the base-corrected airborne value therefore is near 2 nanoTeslas or better. Attribute_Measurement_Frequency: The magnetometer has a recharging interval of 0.5 seconds. The data were recorded at 0.1 second intervals. Attribute: Attribute_Label: resmag Attribute_Definition: residual magnetic value The total magnetic value minus a geomagnetic reference field (GRF), which is a long-wavelength regional magnetic field. The most commonly used reference field is determined from a model developed by the International Association of Geomagnetism and Aeronomy (IAGA). The International Geomagnetic Reference Field (IGRF), is a predictive model adopted at the beginning of a model period (e.g. in 1989 for 1990-1995). After the model period, a revised definitive model is adopted, the DGRF. This is the preferred model to use for removing regional magnetic fields. For this survey, the field removed was the IGRF 1995 updated to the date flown. Values of -9999.9 indicate missing data. Attribute_Definition_Source: Nettleton, L.L., 1971, Elementary Gravity and Magnetics for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series No. 1, p. 83-87. Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -119.44 Range_Domain_Maximum: 659.78 Attribute_Units_of_Measure: nanoTeslas Attribute_Value_Accuracy_Information: Attribute_Value_Accuracy: 2 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. New models are available at five year intervals. These models have varying degrees of accuracy in determining the local reference field. Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: CD-ROM 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 Contact_Voice_Telephone: 303-202-4700 or 1-888-ASK-USGS Contact_Electronic_Mail_Address: www.usgs.gov/pubprod Resource_Description: USGS Open-File Report OFR 02-0361 Distribution_Liability: Although all data published on this CD-ROM 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. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: ASCII Format_Information_Content: Each line contains data in the following format, beginning with line 1(no header included): line_no I5 directn I4 longitud F11.4 latitude F9.4 year I5 jul_day I4 fiducial I7 radar F8.1 barom F8.1 totmag F9.2 resmag F9.2, 1X File_Decompression_Technique: gunzip Digital_Transfer_Option: Offline_Option: Offline_Media: CD-ROM Recording_Format: ISO 9660 Fees: CD-ROM prices are subject to change. Please call or see http://mapping.usgs.gov/esic/prices/ Ordering_Instructions: Detailed instructions can be found at www.usgs.gov/pubprod Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: Web site administration: U.S Geological Survey Central Publications Group Contact_Address: Address_Type: mailing address Address: Central Publications Group USGS MS 902, Box 25046 DFC City: Denver State_or_Province: CO Postal_Code: 80225-0046 Contact_Voice_Telephone: 303-236-5486 Resource_Description: USGS Open-File Report OFR 02-0361 Distribution_Liability: Although all data published on this CD-ROM 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. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: ASCII Format_Specification: Each line contains data in the following format, beginning with line 1 (no header included): line_no I5 directn I4 longitud F11.4 latitude F9.4 year I5 jul_day I4 fiducial I7 radar F8.1 barom F8.1 totmag F9.2 resmag F9.2, 1X File_Decompression_Technique: gunzip Format_Version_Number: 1.1 Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: ftp://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-02-0361 Online_Computer_and_Operating_System: Hewlett Packard 9000/K220 UNIX server running HPUX 11.00 Fees: none Metadata_Reference_Information: Metadata_Date: 20020809 Metadata_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: USGS Gravity and Magnetics contact 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: 80225-0046 Contact_Voice_Telephone: 303-236-1343 Contact_Electronic_Mail_Address: grav_mag@usgs.gov Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998