Airborne geophysical survey: Grand Island 1° x 2° Quadrangle

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Frequently anticipated questions:


What does this data set describe?

Title: Airborne geophysical survey: Grand Island 1° x 2° Quadrangle
Abstract:
Aeromagnetic and aeroradiometric data were collected along flight lines by instruments in an aircraft that recorded magnetic-field and radiometric values and locations. The magnetic data set presents latitude, longitude, altitude, and magnetic-field values. Geologic symbols or codes are also included. The geologic symbols were picked from surficial geologic maps. The radiometric data set presents latitude, longitude, altitude, geologic symbols or codes, apparent Uranium (Bismuth 214), Thorium (Thallium 208), and Potassium (K 40), the element ratios, and ancillary information.
Supplemental_Information:
The U.S. Department of Energy through Bendix Corp. contracted numerous airborne surveys over a period from 1974 to 1981 covering most of the conterminous United States and much of Alaska. The primary purpose was to obtain airborne radiometric data in order to locate and evaluate uranium resources. Aeromagnetic data were also acquired at the same time. In the mid-1980's, all the NURE Program's data were given to the U.S. Geological Survey. The aeromagnetic data were also archived at the National Geophysical Data Center. 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. The U.S. Geological Survey has contracted or flown numerous airborne surveys over a long period (1950's to present). Much of the digital flight-line data have been released to the public through a companion DVD and a web site. Reference is in the Cross-Reference section of this metadata file. A companion CD-ROM/web site has been released containing magnetic data that were generated by digitizing analog maps. The original analog flight-line profiles used to create the analog maps are unavailable. Reference is in the Cross-Reference section of this metadata file. CD's have been released containing the original radiometric flight-line data in various formats. Reference is in the Cross-Reference section of this metadata file.
  1. How might this data set be cited?
    U.S. Department of Energy, U.S. Geological Survey, Department of Interior and the National Geophysical Data Center, NOAA, 2009, Airborne geophysical survey: Grand Island 1° x 2° Quadrangle:.

    Online Links:

    This is part of the following larger work.

    U.S. Geological Survey, Department of the Interior, the National Geophysical Data Center, U.S. Department of Energy, 2009, Aeromagnetic and aeroradiometric data for the Conterminous United States and Alaska from the National Uranium Resource Evaluation (NURE) Program of U.S. Department of Energy: U.S. Geological Survey Open-File Report OFR 2009-1129, U.S. Geological Survey, Denver, CO.

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -100.00
    East_Bounding_Coordinate: -98.00
    North_Bounding_Coordinate: 41.00
    South_Bounding_Coordinate: 40.00
  3. What does it look like?
    http://mrdata.usgs.gov/geophysics/surveys/NURE/grand_island/grand_island.jpg (JPEG)
    Reduced-size image depicting the data, 935 x 697 pixels, 199,289 bytes
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 27-Jul-1977
    Ending_Date: 09-Aug-1977
    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.
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: tabular digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a point data set.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0001. Longitudes are given to the nearest 0.0001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6,378,206.4.
      The flattening of the ellipsoid used is 1/294.98.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: National Geodetic Vertical Datum of 1929
      Altitude_Resolution: 0.1
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:
      Explicit elevation coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    Airborne survey specifications These items are constant for the entire survey Project number: 6038D Project name: Grand Island Quadrangle Survey flown by: Texas Instruments, Inc. Survey flown for: DOE Grand Junction Office Approx. no. of line miles: 1746 Survey height: 400 ft Altitude method: Draped over terrain Flight-line spacing: 5 miles Flight-line direction: East-West Aircraft used: Douglas DC-3 Airport - arrival: unknown Airport - departure: unknown Magnetometer used: proton precession Sensor tow distance: 100 feet Radiometric crystal package volume: 3324 (down) & 415 (up) cu. in.
    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. Grasty, R.L., and Holman, P.B., 1974, Optimum Detector Sizes for Airborne Gamma-ray Surveys: Geological Survey of Canada Paper 74-1, Part B, p. 72-74.
    Entity_and_Attribute_Overview:
    Aeromagnetics Each record contains the following 13 attributes: No name contents 1 line flight line number 2 fid fiducial number (integer) 3 time time (hhmmss) 4 day Julian day flown (integer) 5 year year flown (integer) 6 latitude latitude (decimal degrees) 7 longitude longitude (decimal degrees) 8 radalt radar altimeter reading above ground (meters) 9 totmag corrected magnetic value (nT) 10 resmag residual magnetic value (nT) 11 diurnal ground magnetometer value (nT) 12 geology surficial geology beneath flight line (coded) 13 resmagCM4 resmag calculated using the comprehensive model (nT)
    Entity_and_Attribute_Overview:
    Radiometrics Each record contains the following 21 attributes: No name contents 1 line flight line number 2 fid fiducial number (integer) 3 time time (hhmmss) 4 day Julian day flown (integer) 5 year year flown (integer) 6 latitude latitude (decimal degrees) 7 longitude longitude (decimal degrees) 8 radalt radar altimeter reading above ground (meters) 9 resmag residual magnetic value (nT) 10 geology surficial geology beneath flight line (coded) 11 qual quality flags of the radiometrics (integer) 12 app_K apparent Potassium as Potassium 40 (percent potassium) 13 app_U apparent Uranium as Bismuth 214 (parts per million equivalent uranium) 14 app_Th apparent Thorium as Thallium 208 (parts per million equivalent thorium) 15 U_Th_ratio ratio of Uranium and Thorium 16 U_K_ratio ratio of Uranium and Potassium 17 Th_K_ratio ratio of Thorium and Potassium 18 total_count total count of radioactivity (counts/second) 19 atmos_BI214 atmospheric Uranium as Bi214 (counts/second) 20 air_temp air temperature (degrees Celsius) 21 air_press air pressure (mmHg)
    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. Ravat, D., T. Sabaka, A. Elshayat, A.Aref, E. Elawadi, R.P. Kucks, P. Hill, J.D. Phillips, C.A. Finn, C. Bouligand, R. Blakely, 2008, A Preliminary Full Spectrum Magnetic Anomaly Database of the United States With Improved Wavelengths for Studying Continental Dynamics, Invited Paper, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract GP52A-02. Sabaka, T.J., Olsen, N., and Langel, R.A., 2002, A Comprehensive Model of the Quiet-Time Near-Earth Magnetic Field; Phase 3: Geophysical Journal International, v 151, no. 1, p. 32-68. Parasnis, D.S., 1975, Mining Geophysics: Elsevier Scientific Publishing Company, Methods in Geochemistry and Geophysics vol. 3, p. 298-307.
    record for one magnetic or radiometric data point
    The set of all measurements reported for a magnetic or radiometric data point having the same spatial location. (Source: Standard aeromagnetic and aeroradiometric data collection procedures as written in the contract for survey collection.)
    line
    flight line number (Source: often assigned by airborne survey crew)
    Range of values
    Minimum:15
    Maximum:212
    Units:alphanumeric value
    fid
    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. (Source: Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists, p. 89.)
    Range of values
    Minimum:1
    Maximum:2708
    time
    time of data point collection. Time is given in either local time or Greenwich Meridian Time. Values of 999999 indicate missing data. (Source: self evident) a range of time of day values has no meaning because the timeframe can span several days or weeks.
    day
    Julian day, where Jan. 1 = 1 and Dec. 31 = 365 or 366 (leap year) (Source: self evident)
    Range of values
    Minimum:208
    Maximum:221
    year
    year of data point collection (Source: self evident)
    Range of values
    Minimum:1977
    Maximum:1977
    latitude
    latitude - geographic coordinate (Source: self evident)
    Range of values
    Minimum:40.0004
    Maximum:40.9991
    Units:decimal degrees
    longitude
    longitude - geographic coordinate (Source: self evident)
    Range of values
    Minimum:-99.9994
    Maximum:-98.0000
    Units:decimal degrees
    radaralt
    radar altimetry reading, in meters 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 -999.9 indicate missing data. (Source: Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists, p. 89.)
    Range of values
    Minimum:70.4
    Maximum:246.3
    Units:meters
    totmag
    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. Records containing missing data were usually deleted. (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.)Frequency of measurement: The magnetometer has a recharging interval of 0.5 seconds. The data were recorded at 1 second intervals.
    Range of values
    Minimum:55973.0
    Maximum:57957.0
    Units:nanoTeslas
    resmag
    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 epochs when CM models are not available. For this survey, the field removed is probably IGRF 1965. Some contractors add a constant to the residual value in order to avoid negative values. This constant can vary from one data set to another. Values of -9999.9 indicate missing data. (Source: Nettleton, L.L., 1971, Elementary Gravity and Magnetics for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series No. 1, p. 83-87.)
    Range of values
    Minimum:-1031.0
    Maximum:657.0
    Units:nanoTeslas
    diurnal
    Base magnetometer values used to correct the total magnetic value. 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 called the diurnal. The magnetic changes may have an amplitude of 20 to 50 nanoTeslas. The diurnal is monitored during the survey and if changes are 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. (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.)Frequency of measurement: The base magnetometer has a recharging interval of 0.5 seconds. The data were recorded at 2-4 second intervals.
    Range of values
    Minimum:57595.2
    Maximum:57659.0
    Units:nanoTeslas
    geology
    Geologic identification codes or numeric codes indicating the rock types immediately beneath the flight line. These codes were determined by plotting the flight lines on a surficial geologic map. A description of the codes can be found in the GJBX- or GJO- report for this quadrangle listed in the Cross Reference section above. Values of -99 indicate missing data. (Source: original publication) values are not quantified
    resmagCM4
    The total magnetic field value minus the core component of geomagnetic field is known as the comprehensive model (CM). CM4 (the fourth generation of CM) is the modern reference field determined from a long-wavelength spatially and temporally continuous model of the geomagnetic field that simultaneously considers the Earth’s core, lithospheric, and external magnetic fields (external ionospheric and magnetospheric fields and the components induced by them inside the Earth). Spherical harmonic degree 13 of CM4 is the preferred model to use for removing regional magnetic fields for the time periods it is valid for (1960 to June 2002). Values of -9999.9 indicate missing data. (Source: Ravat, D., T. Sabaka, A. Elshayat, A.Aref, E. Elawadi, R.P. Kucks, P. Hill, J.D. Phillips, C.A. Finn, C. Bouligand, R. Blakely, 2008, A Preliminary Full Spectrum Magnetic Anomaly Database of the United States With Improved Wavelengths for Studying Continental Dynamics, Invited Paper, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract GP52A-02. Sabaka, T.J., Olsen, N., and Langel, R.A., 2002, A Comprehensive Model of the Quiet-Time Near-Earth Magnetic Field; Phase 3: Geophysical Journal International, v 151, no. 1, p. 32-68.) range of values were not determined
    apparent potassium
    the apparent content of potassium in the surface rock and soil Values of -99.9 indicate missing data. (Source: Duval, J. S., 1990, Modern aerial gamma-ray spectrometry and regional potassium map of the conterminous United States: Journal of Geochemical Exploration, vol. 39, no. 1-2, p. 249-253.)Frequency of measurement: The data were recorded at 1-2 second intervals.
    Range of values
    Minimum:-903.3
    Maximum:8698.3
    Units:percent potassium
    apparent uranium
    the apparent content of uranium in the surface rock and soil Values of -99.9 indicate missing data. (Source: Duval, J. S., 1990, Modern aerial gamma-ray spectrometry and regional potassium map of the conterminous United States: Journal of Geochemical Exploration, vol. 39, no. 1-2, p. 249-253.)Frequency of measurement: The data were recorded at 1-2 second intervals.
    Range of values
    Minimum:-980.3
    Maximum:9935.1
    Units:parts per million equivalent uranium (ppm eU)
    apparent thorium
    the apparent content of thorium in the surface rock and soil Values of -99.9 indicate missing data. (Source: Duval, J. S., 1990, Modern aerial gamma-ray spectrometry and regional potassium map of the conterminous United States: Journal of Geochemical Exploration, vol. 39, no. 1-2, p. 249-253.)Frequency of measurement: The data were recorded at 1-2 second intervals.
    Range of values
    Minimum:-875.6
    Maximum:6707.2
    Units:parts per million equivalent thorium (ppm eTh)
    total count
    the gross effect of the content of uranium, thorium, and potassium in the surface rock and soil Values of -9999.9 indicate missing data. (Source: Pitkin, James A., 1968, Airborne measurements of terrestrial radioactivity as an aid to geologic mapping: U.S. Geological Survey Professional Paper 516-F, 29 p.)Frequency of measurement: The data were recorded at 1-2 second intervals.
    Range of values
    Minimum:-15,598.7
    Maximum:454,731.4
    Units:counts per second
    atmospheric bismuth 214
    the atmospheric content of equivalent uranium determined by measuring the amount of its decay product bismuth 214. Values of -99.9 indicate missing data. (Source: Duval, J. S., 1990, Modern aerial gamma-ray spectrometry and regional potassium map of the conterminous United States: Journal of Geochemical Exploration, vol. 39, no. 1-2, p. 249-253.)Frequency of measurement: The data were recorded at 1-2 second intervals.
    Range of values
    Minimum:11.4
    Maximum:60.9
    Units:parts per million
    air temperature
    temperature of the air in degrees Celsius Values of -999.9 indicate missing data. (Source: self evident)
    Range of values
    Minimum:-999.9
    Maximum:-999.9
    air pressure
    pressure of the air measured in millimeters of mercury (mmHg) Values of -999.9 indicate missing data. (Source: self evident)
    Range of values
    Minimum:-999.9
    Maximum:-999.9
    qual
    quality flags indicating the relative quality of the radiometric data. A description of the codes can be found in the GJBX- or GJO- report for this quadrangle listed in the Cross Reference section above. Values of -9999 indicate missing data. (Source: original publication) values are not quantified
    U-Th ratio, U_K ratio, and Th_K ratio
    The calculated ratios of uranium, thorium, and potassium. Values of -99.9 indicate missing data. (Source: self evident) ranges of values were not determined

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Department of Energy, U.S. Geological Survey, Department of Interior and the National Geophysical Data Center, NOAA
  2. Who also contributed to the data set?
    These USGS employees contributed to reformatting and archiving these data: Pat Hill, Bob Kucks, Rick Saltus, Ron Sweeney, Sarah Shearer Cooperating contributors from the National Geophysical Data Center are: Ronald Buhmann, David Dater, Susan McLean, Stewart Racey The Comphrensive Model data were supplied by: Prof. Dhananjay Ravat, University of Kentucky
  3. To whom should users address questions about the data?
    USGS Gravity and Magnetics Contact
    U.S. Geological Survey
    Box 25046 Mail Stop 964
    Denver Federal Center
    Denver, CO

    303-236-5652 (voice)

Why was the data set created?

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. Aeroradiometric surveys measure the radiation emanating from the earth's surface, which provides general estimates of the geographic distribution of uranium, thorium, and potassium in surficial and some bedrock units. Bismuth 214 and Thallium 208 are decay products of Uranium and Thorium. Along with Potassium 40 they give identifiable peaks in the gamma-ray spectra of naturally occurring radiation. The element data and the ratios of the element data are used to help map surficial geology and to detect concentrations of radioactive minerals.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 1977 (process 1 of 2)
    Conversion of measured values to geographic position and magnetic and radiometric 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 Conversion processes, if reported, may be found in the U.S. Department of Energy's published GJO- or GJBX- reports for the quadrangle or group of quadrangles. Unpublished products generated by the contractor included magnetic tapes and perhaps some written documentation.
    Date: 2008 (process 2 of 2)
    USGS reformatting of contractor data to standard format. USGS personnel used the software package Oasis Montaj version 6.3 by Geosoft, Inc., to read in the original contractor's data. Positioning and magnetic values were checked for obvious errors or spikes. Values of -9999.9,-999.9, -99.9, etc., were given where the value could not be reasonably corrected or, in some cases, the whole record was removed. Information that was missing from the data file but recorded elsewhere, such as year flown, was added th the file. The radiometric data were not checked for errors except for dummy values which were replaced with -99.9, -999.9, etc. The reformatted data files were written in the format described in the section on Entity_and_Attribute_Overview.
  3. What similar or related data should the user be aware of?
    U.S. Geological Survey, 1999, Digitized Aeromagnetic Datasets of the Conterminous United States, Hawaii, and Puerto Rico: U.S. Geological Survey Open-File Report OFR 99-557, U.S. Geological Survey, Denver CO.

    Online Links:

    Other_Citation_Details:
    CD-ROM or online files Complements this publication with analog data
    U.S. Geological Survey, 2002, Digital Aeromagnetic Datasets of the Conterminous United States and Hawaii: U.S. Geological Survey Open-File Report OFR 02-361, U.S. Geological Survey, Denver CO.

    Online Links:

    Other_Citation_Details:
    CD-ROM or online files Complements this publication with digital data
    U.S. Geological Survey, 1999, Aerial Gamma-Ray Surveys of the Conterminous United States and Alaska: U.S. Geological Survey Open-File Report OFR 99-0562-A through -M, U.S. Geological Survey, Denver CO.

    Other_Citation_Details: Thirteen CD-ROMs
    U.S. Department of Energy (DOE) Grand Junction Office, 1978, Aerial radiometric and magnetic reconnaissance survey of portions of the Great Plains and Central Lowlands: Grand Junction Bendix Office Report (GJBX) GJBX-100(78), DOE Grand Junction Office, Grand Junction, Colorado.

    Other_Citation_Details:
    map scale 1:500,000 Author(s): Texas Instruments, Inc.
    U.S. Department of Energy (DOE) Grand Junction Office, 1981, Grand Island Quadrangle, residual intensity magnetic anomaly profile and contour maps: Grand Junction Map Open-file Report GJM-012, DOE Grand Junction Office, Grand Junction, Colorado.

    Other_Citation_Details: 4 sheets, map scale 1:250,000

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    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.
  2. How accurate are the geographic locations?
    Flight Path Recovery The horizontal position of the survey aircraft used to collect data was determined by reconciling down-looking photographs (recorded on continuous-strip film) with topographic maps and orthophotoquadrangle maps. Fiducial numbers and marks, impressed on any paper strips that were recording data or added to magnetic tape records, were included as a function of time to further reconcile location with instrumentation.
  3. How accurate are the heights or depths?
    The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter. Barometric altimeter data are not available for most of these data sets. Radar altimeters are estimated to have an error of 2-5% of the altitude (Richard Hansen, PRJ, Inc., written communication). The magnetometer was carried in a bird towed on a line about 100 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 less than the length of the line but remains constant for the survey.
  4. Where are the gaps in the data? What is missing?
    Loss of data due to poor transmission, channel dropout, obvious spiking, missing channels, and other obvious errors were replaced with one of the Following values: -9999.9, -999.9, -99, etc. Sometimes channels were added and filled with dummy values (-9999.9, etc.) to comply with the established format. Records that had no usable data were deleted.
  5. How consistent are the relationships among the observations, including topology?
    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, radiometic crystal packages, 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.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
Use_Constraints:
none. Acknowledgement of the U.S. Geological Survey, National Geophysical Data Center, U.S. Department of Energy, and Prof. Dhananjay Ravat would be appreciated in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 2)
    Web site administration: U.S Geological Survey Central Publications Group
    Central Publications Group
    USGS MS 902, Box 25046 DFC
    Denver, CO

    303-236-5486 (voice)
  2. What's the catalog number I need to order this data set? USGS Open-File Report OFR 2009-1129
  3. What legal disclaimers am I supposed to read?
    Although all data published on this web site 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.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: ASCII (version 2.1) Magnetic data file Each line contains data in the following format, beginning with line 1 (no header included): line I6 fid I8 time I8 day I5 year I6 latitude F10.4 longitude F11.4 radalt F7.1 totmag F9.1 resmag F9.1 diurnal F9.1 geology A10 resmagCM4 F9.1 Radiometric data file Each line contains data in the following format, beginning with line 1 (no header included): line I6 fid I8 time I8 day I5 year I6 latitude F10.4 longitude F11.4 radalt F7.1 resmag F9.1 geology A10 qual A8 app_K40 F9.1 app_U_BI214 F9.1 app_Th_TL208 F9.1 U_Th_ratio F7.1 U_K_ratio F7.1 Th_K_ratio F7.1 total_count F10.1 atmos_BI214 F7.1 air_temp F8.1 air_press F8.1
      Network links: http://pubs.usgs.gov/of/2009/1129
    • Cost to order the data: none


  1. Who distributes the data set? (Distributor 2 of 2)
    Peter N Schweitzer
    USGS Eastern Mineral and Environmental Resources Science Center
    Geologist
    12201 Sunrise Valley Drive
    Reston, VA
    USA

    703-648-6533 (voice)
    703-648-6252 (FAX)
    pschweitzer@usgs.gov
  2. What's the catalog number I need to order this data set? grand_island_meta.txt
  3. What legal disclaimers am I supposed to read?
    This dataset was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 04-Dec-2014
Metadata author:
USGS Gravity and Magnetics contact
U.S. Geological Survey
Box 25046 Mail Stop 964
Denver Federal Center
Denver, CO

303-236-5652 (voice)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://mrdata.usgs.gov/geophysics/surveys/waf/GRAND_ISLAND_META.faq.html>
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