Calibration gamma ray spectra processing (C07a)
Contents
1. 256 channel survey data Spectrometer Drift Library Help Top Spectrometers are subject to drift mainly due to temperature and voltage fluctuations The drift affects the mapping of the peak energies onto the channel ranges and therefore the count rate of the measured photopeaks For this example we shall analyse the cookrad DIR dataset for spectrometer drift 1 From the Intrepid Project Manager launch the Calibration Spectra Processing Tool 2 Under the Files menu choose Select Input Data Select the install_path sample_data cookbooks radiometrics cookrad DIR dataset Select the input spectrum field Choose spectrum which is the raw spectrum data This will be used to compute the drift plots 3 Click on Select Input Calibration File Although the tool will not use this file you still need to select one Choose dfa_default asc Click OK to dismiss the Input Data Selection box 4 Under the Options menu select Display Calibration Spectra and click OK Then select Quality Control Both options must be turned on In the Quality Control Box enter low and high channel limits for photo peaks These can be found by using the View function and displaying spectra in the Multi Channel Processing tool Select the Peak Drift from Energy Calibration option Select Energy Calibrate by Line Choose OK to dismiss the box 5 Choose Apply QC channel drift plots for the Radon K U and Th peaks will be drawn on the screen along with2. and click OK Then select Quality Control Both options must be turned on In the Quality Control Box enter low and high channel limits for photo peaks These can be found by using the View function and displaying spectra in the Multi Channel Processing tool Select the Peak Drift from Energy Calibration option Select Energy Calibrate by Line Then select Peak Resolution Choose OK to dismiss the box Choose Apply QC resolution plots for the Radon K U and Th peaks will be drawn on the screen along with calibration spectra plots from the specified calibration file 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C07a 8 Library Help Top lt 4 Back gt 6 Here is an example of a QC resolution plot for the Potassium peak Intrepid Calibrate 256 3 7 release cut QC Resolution Plot Potassium 10 00 83 00 Line Number Dismiss Frequently asked questions Q Why do I need to load a dataset and a calibration file if only one is being used A Future development work on this tool will remove this requirement References Grasty R L and Minty B R S 1995 A Guide to the Technical Specifications for Airborne Gamma Ray Surveys Australian Geological Survey Organisation Record 1995 60 Canberra IAEA 1991 Airborne gamma ray spectrometer surveying Technical Report Series No 328 Internation
3. 07a 3 Library Help Top lt 4 Back gt How calibration data is acquired In the case of the aircraft and cosmic background corrections the aircraft flies a high altitude stack series of lines over water at a series of different heights In the case of the radon background correction the aircraft collects data over water with little or no radon and again when there is a lot of radon over water In the case of the height attenuation and conversion factors the aircraft flies an altitude stack over a nominated line over a dynamic test area at a series of heights which would be encountered during a typical radiometric survey In the case of Compton stripping ratios data is gathered by placing the individual spectometer packs over specially calibrated pads for several minutes These data determine the stripping ratios for the spectrometer Before the advent of routine 256 channel radiometric data collection and processing it was standard practice to perform the background corrections on the windowed data prior to the Compton stripping correction In this case the calibration flight data was used to compute a single cosmic and aircraft background coefficient each for K U Th and TC Radon background corrections were typically also done as window corrections using upward looking detectors With 256 channel processing the background corrections can be done as full spectrum corrections The window coefficients are replaced by spectr
4. 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C07a 6 Library Help Top 4 Back gt 4 Under the Files menu choose Save Output Data Choose Select Output Calibration File and specify a name for the new calibration file ie cal_flights asc It will be written to the install_path config calibration_spectra directory 5 Under the Options menu select Display Calibration Spectra and click OK Then select Create Calibration Spectra Both options must be turned on In the Create Calibration Spectra box choose Cosmic and Aircraft Background and select the cosmic field from the dataset Choose OK to dismiss the box 6 Choose Apply The tool will pause for a few seconds before calculating spectra from the calibration dataset and drawing graphs of the spectra onto the screen Notice that for this calibration dataset the computed aircraft spectrum looks acceptable but the computed cosmic spectrum looks flat and unacceptable We can conclude from this that the data cannot be used to provide a useable cosmic calibration 7 The spectra will be written to the output file In this case the output file will contain the computed cosmic and aircraft spectra Because no radon spectrum was computed the radon spectrum from the input file will be copied to the output file Quality Control Functions The Calibration Processing tool provides some additional quality control functions for
5. INTREPID User Manual Calibration gamma ray spectra processing C07a 1 Library Help Top lt 4 Back gt Calibration gamma ray spectra processing C07a veh Library Help Top This cookbook provides an introduction to the INTREPID Calibration Spectra Processing tool It includes a worked example which demonstrates how to use the tool to generate calibration asc files from calibration flight data Calibration files are an essential requirement for running the INTREPID Multi Channel Radiometric Processing tool The Calibration Spectra Processing tool provides the following main functions e graphically displays cosmic aircraft and radon spectra from INTREPID calibration files creates INTREPID calibration files containing cosmic and aircraft spectra from calibration flight data It also provides the following Quality Control QC functions reports full width half maximum FWHM resolution and spectrometer channel drift of Radon K U and Th photo peaks from 256 channel survey data e detects and reports Null and zero spectra in 256 channel survey data Location of sample data for Cookbooks Where install_path is the path of your INTREPID installation the project directory for the Cookbooks sample data is install_path sample_data cookbooks For example if INTREPID is installed in C Program Files Intrepid Intrepid4 5 then you can find the sample data at C Program Files Intrepid Intrepid4 5 sample_data co
6. a which have a single value for each channel Consequently the corrections can be performed more accurately than is possible using windowed data For example we remove the aircraft background by subtracting a 256 channel aircraft background spectrum directly from the measured spectrum for each data point The cosmic background spectrum is a 256 channel spectrum used as a unit vector of coefficients We multiply this spectrum by the measured cosmic window one of the ancillary parameters at each data point to give the cosmic background correction and subtract it from the measured spectrum The radon background spectrum is a 256 channel pure Radon channel spectrum It is required by the spectral ratio method to remove atmospheric radon contamination The following illustration shows a typical aircraft and cosmic background spectrum Calibration Spectrum Plot Calibration Spectrum Plot Aircraft Background Spectrum Cosmic Background Spectrum K n 256 00 0 00 128 00 256 00 128 00 Channel Number Channel Number Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C07a 4 Library Help Top 4 Back gt Calibration file requirements for Multi Channel Processing The INTREPID Multi Channel Processing tool requires a cosmic aircraft and radon spectrum collected across the fu
7. ad DIR dataset 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C07a 5 Library Help Top lt 4 Back gt 3 Choose Select Input Calibration File A chooser will appear showing the selection of calibration asc files from inside the install_path config calibration_spectra directory Choose cosmic_radon_jwf asc This calibration file was previously compiled for the Multi Channel Processing cookbook Click OK to dismiss the Input Data Selection box Select Input Data all fields must be selected even if not used n Select Input Data all fields must be selected kyen if not used Input Data Selection Parameters Select Line Dataset C jintrepid int37c226 cookbook radiometrics cookrad Select Input Calibration File C Intrepid int3 7c226 config calibration_spectra cosmic_radon_jwf Select nput Calibration Fite p Select Input Spectrum Field Sample Interval seconcls OK Cancel 4 Under Options select Display Calibration Spectra The data will be displayed as separate graphs Choose OK to dismiss the box 5 Now choose Apply The tool will pause for a few seconds before drawing graphs of the various calibration spectra contained within the calibration file The calibration file cosmic_radon_jwf asc contains spectra for cosmic aircraft and radon 6 When you have finished the exercise exit from the tool Create new calibration files fro
8. al Atomic Energy Agency Vienna Library Help Top 2012 Intrepid Geophysics lt 4 Back gt
9. calibration spectra plots from the specified calibration file 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C07a 7 Library Help Top 4 Back gt 6 Here is an example of a channel drift plot for the Potassium peak Some peak drift is evident during the latter part of the survey Intrepid Calibrate 256 v3 7 release out QC Channel Drift Plot Potassium 82 Line Number Dismiss Peak Resolutions The precision with which a spectrometer can measure gamma ray energies is known as the system resolution Resolutions can be calculated for each of the main photo peaks Peak resolutions are calculated from the spectrum peaks using the full width half maximum FWHM rule Steps 1 to 3 are the same as before 1 Library Help Top From the Intrepid Project Manager launch the Calibration Spectra Processing Tool Under the Files menu choose Select Input Data Select the install_path sample_data cookcooks radiometrics cookrad DIR dataset Select the input spectrum field Choose spectrum which is the raw spectrum data This will be used to compute the peak resolution plots Click on Select Input Calibration File Although the tool will not use this file you still need to select one Choose dfa_default asc Click OK to dismiss the Input Data Selection box Under the Options menu select Display Calibration Spectra
10. ll 256 channel spectrum to apply the complete background corrections However particularly for older surveys this calibration data may not be available for your survey Ifyou do have multi channel cosmic and aircraft calibration flight data then you can use the Calibration Spectra Processing tool to derive a new calibration file containing the correct full spectra cosmic and aircraft backgrounds prior to running the corrections in the Multi Channel Processing tool Ifyou do not have multi channel cosmic and aircraft calibration flight data but you do have cosmic and aircraft coefficients for the standard TC K U Th windows you can run the cosmic and aircraft corrections as standard window corrections in the standard_3_corrections tool rather than as full spectra corrections in the Multi Channel Processing tool Ifyou do not have multi channel cosmic and aircraft calibration flight data and no supplied window background coefficients often the case for older surveys you may use a supplied calibration file in the Intrepid config calibration_spectra sub directory corresponding to your survey height While you will be using aircraft and cosmic background parameters derived from a different survey this approach will still allow you the full benefits of multi channel processing options such as spectral noise cleaning and radon removal Note The pure radon spectrum changes little from one installation to another In all cases you ca
11. m calibration flight data In the following worked example we will use some actual calibration data to generate a calibration file The calibration data was acquired by a helicopter for the purpose of generating cosmic and aircraft background correction spectra It consists of 11 lines flown at different altitudes The data has already been imported into a INTREPID line dataset It is called cal_flights DIR and can be found in the install_path sample_data cookbooks radiometrics directory To achieve the best results from the calibration data some pre processing was done Multi Channel processing was run on the calibration data using the following options NASVD 4 components Energy calibration e Livetime correction Save processed spectrum This is the spectrum that will be used to compute the background spectra ie spectrum_NASVD_Ecal_Live 1 From the Intrepid Project Manager launch the Calibration Spectra Processing tool 2 Under the Files menu choose Select Input Data Click on Select Line Dataset and select the calibration dataset ie cal_flights DIR Make sure the Input Spectrum field selected is spect rum_NASVD_Ecal_Live 3 Click on Select Input Calibration File The file you choose here will serve as a template for the new output calibration file Choose dfa_default asc This calibration file contains a cosmic aircraft and a radon spectra Click OK to dismiss the Input Data Selection box Library Help Top
12. n use a radon spectrum from a pre existing calibration file which corresponds to your survey height These are a series of high quality Radon spectrums collected by GA Geoscience Australia Display calibration spectra from existing calibration files Library Help Top Radiometric calibrations tend to be carried out infrequently but care must be taken in the collection and reduction of the data Calibration data needs to be checked carefully before use as poorly collected or reduced data will affect the processed survey data quality To this end it may be helpful to view INTREPID calibration files graphically on the screen We shall do this using an existing calibration file located in the install1_path config calibration_spectra directory Note For all Calibration Spectra Processing options a 256 channel Line Dataset and an Input Calibration asc file must be chosen even if the dataset or the calibration file are not being used by that process 1 From the Intrepid Project Manager launch the Calibration Spectra Processing tool 2 Under the Files menu choose Select Input Data A dialog box will appear Choose Select Line Dataset and select the 256 channel dataset cookrad DIR which is located under cookbooks radiometrics If the cookrad DIR dataset already has an aliased spectrum field it will appear alongside the Select Input Spectrum Field box If the box remains blank you must nominate a spectrum from the cookr
13. okbooks For information about installing or reinstalling the sample data see Sample data for the INTREPID Cookbooks in Using INTREPID Cookbooks R19 For a description of INTREPID datasets see Introduction to the INTREPID database G20 For more detail see INTREPID database file and data structures R05 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C07a 2 Library Help Top 4 Back gt Background theory Library Help Top The correction process for multi channel spectra includes Spectral noise reduction using either the NASVD or MNF method e Live time Dead time Energy Calibration also referred to as Drift Cosmic and Aircraft background e Radon background After the multi channel corrections it is normal to create new windowed data You would then apply the following corrections to the windowed data Compton stripping e Height attenuation Conversion to radio element ground concentrations Before you perform these corrections on radiometric data you need to calibrate the airborne acquisition system Calibration is achieved using a series of test flights and test pad measurements The data from these calibrations is used to compute the various coefficients or spectra required to perform the radiometric corrections 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Calibration gamma ray spectra processing C
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