Tutorial 1: Processing Airborne Data

Database Setup

A table of the database fields that are required to be present in the database for processing airborne radiometric data, and the preferred data types, can be found here. Note the sections on the treatment of null values and database restrictions. An explanation of all the fields that are created during processing can be found here.

Use either Intrepid or Oasis Montaj to set up all the input (pre-existing) database fields required for processing. The processing steps described below are for processing an airborne dataset using the spectral-ratio method for background estimation. Therefore, no upward-looking detector spectra are required for this tutorial.

Processing Steps

Run GammaSpec by double-clicking the desktop icon. Take a moment to familiarise yourself with the main window. The processing sequence is described in the Messages listBox and follows a left-to-right navigation across the Main Window menu strip. We are going to process the data as follows:

Open a database:                         File ...

Set database aliases:                   Settings|Set Aliases  ...

Set processing parameters:         Settings|Set Parameters ...

Do NASVD noise reduction:         NASVD ...

Energy-calibrate the spectra:        Energy Calibration ...

Sample the IAEA windows:           Window ...

Apply gamma corrections:            Corrections ...


  1. Open a database – File|Open Intrepid Database. (or Open Geosoft Database for Oasis Montaj). Navigate to the "demo_data\airborne_spectrometry\processing_spectral_ratio" folder. Then select the Intrepid database "PROCESSING_SPECTRA_RATIO..DIR" (for Oasis Montaj, select "processing_spectral_ratio.gdb") and click Open (or just double-click the database name). This returns you to the main window – note the database panel on the Main Window now shows information about the database. Check the Messages listBox for any messages. 
  2. Set the database aliases – Settings|Set Aliases. The left column of the Set Aliases window shows the aliases for database fields that must already exist in the database. The right column are fields that will be created if they don't already exist. The third column shows a selection listBox of fields that are in the database. There are 3 ways to set the aliases. We are going to use the easy way – click the Load From File button, and open the "alias_processing.pc" program control file. This loads the aliases from the file. Click the Help button to display a sample alias control file with explanations of all the aliases. Click Save And Return to return to the main window. Check the Messages listBox for any messages. 
  3. Set the processing parameters – Settings|Set Parameters. The parameters are grouped by processing step. There are 2 ways to set the parameters. Guess which way we're going to use? – click the Load From File button, and open the "parameters_processing_spectral_ratio.pc" program control file. This loads the parameters from file. Click the Help button to display a sample parameter control file with explanations of all the parameters. If you are using the Full-spectrum method for cosmic/aircraft background removal, then make sure that the Cos/Air spec file textBox is set to the full path to the file located at "demo_data\airborne_spectrometry\processing_spectral_ratio\aircraft_and_cosmic_spectra.txt". If necessary, click the file icon button to navigate to the file. Click Save And Return to return to the main window. Check the Messages listBox for any messages.

Tool Tip:  If you are using the manual method for energy calibration of the multichannel spectra, then the approximate position of the Th photopeak is a critical parameter, and is required by most GammaSpec tools. Use View Spectra to estimate this parameter – see the Tool Tip for View Spectra in the Viewing Data tutorial on how to do this.

We have now set all the aliases and parameters for all the processing steps! In fact, the aliases are now also set for all the View Menu tools. We can now proceed to process the data.

  1. NASVD noise reduction – NASVD|Run NASVD on Downward Spectra. This starts the NASVD processing. This process may take a few minutes to run – depending on the number of CPU's available on your machine. In the meantime, check the log files. Click File|View System Log File to view the system log. This logs debug information, warnings and error messages (tagged as [INF], [WRN] and [ERR] after the date/time stamp). You can safely ignore the warning "numNulls>0 for channel nasvdAmplitudes" as this is being updated by the NASVD process. Click File|View User Log File to view the User Log. This records information on all the processing steps since the database was opened. For more information on log files see Using Log Files. When the NASVD processing completes, check the Messages listBox for any messages. If anything goes wrong, always check the Messages listBox, and the System and User Log files. The Main Window chart shows the 16 lowest-order eigenvectors for the each group processed. You can view these at your leisure later using the View Eigenvectors tool (View|View Eigenvectors).
  2. Energy Calibration – Energy Calibration|EnergyCalibrate Downward Spectra. This launches the energy-calibration process. The results are stored as new database fields called "base" and "gain" – the energy at the bottom of channel 1 for each spectrum (in MeV), and the width (in MeV) of the channels for each spectrum. Check the Messages listBox for any messages. 
  3. Windowing – Window|Sample Raw Downward Spectra Windows. This samples the standard IAEA windows (TC, K, U and Th) for the raw spectra, and creates the database fields associated with the following aliases – "Total Count Raw", "Potassium Raw", "Uranium "Raw" and "Thorium Raw". When this completes, also run Window|Sample NASVD Downward Spectra Windows. This samples the standard IAEA windows (TC, K, U and Th) for the Nasvd spectra, and creates the database fields associated with the following aliases – "Total Count Nasvd", "Potassium Nasvd", "Uranium Nasvd" and "Thorium Nasvd". The windowing tool also corrects the window data for live time. Check the Messages listBox for any messages. 
  4. Corrections – Corrections|Apply Gamma Corrections. This corrects the livetime-corrected window data for aircraft and cosmic background, radon background, channel interaction correction (stripping) and window sensitivities. The output from this process are elemental concentrations (% K, ppm eU and ppm eTh). If the input to this process is the raw window count rates, then the tool will create the output database fields associated with the following aliases (if they don't already exist) – "Potassium Corrected", "Uranium Corrected" and "Thorium Corrected". If the input to this process is the Nasvd window count rates, then the tool will create the output database fields associated with the following aliases – "Potassium Nas Corr", "Uranium Nas Corr" and "Thorium Nas Corr". Check the Messages listBox for any messages.

This completes GammaSpec's processing of the radiometric data. Use the View Flight Path tool to view the results – View|View Flight Path. There is a tutorial on how to use this tool here. But give it a go now anyway. You have to click the Apply button to plot the flight path. You can open up more than one instance of this tool at a time, but you can't run this tool while other processing is taking place. Compare the raw U data ("uranium_nas") with the corrected U data ("uranium_nas_corr"). If the results are unsatisfactory, repeat some, or all, of the processing steps using different parameters – this is an iterative process. Otherwise, you can proceed to finalise the processing in Intrepid or Oasis Montaj using cross-over tie levelling and/or decorrugation followed by final gridding.

Processing Upward-Looking Detector Data

If you want to try your hand at processing upward-looking detector data, a demonstration dataset can be found in the demo_data\airborne_spectrometry\processing_upward_detector directory. Use the alias and parameter control files in the directory. The processing sequence is almost exactly the same as above, except for two extra processing steps:

    • After energy-calibrating the downward spectra, do the same for the upward spectra – Energy Calibration|EnergyCalibrate Upward Spectra.
    • After windowing the downward spectra windows, do the same for the upward spectra uranium window – Window|Sample Raw Upward Uranium Window