Tutorial 7: Radon Stripping – Test-Lines Calibration

Database Setup

This tool calculates the c1 coefficient required by the spectral-ratio method for estimating atmospheric radon background. It also calculates the TC, K and Th radon stripping coefficients, and the upward-detector au coefficient (if required).

 The tool uses the daily test lines flown at the start and end of each day to obtain a radon spectrum. The test line is about 8 km long and is flown at least twice a day to monitor environmental changes, such as soil moisture, and as a final check on the sensitivity of the detector. If we assume that the soil moisture content is constant, and since aircraft and cosmic background are constant for a particular altitude, then the difference between any two lines is due to changes in atmospheric radon. The tool calculates the difference between the test line whole-line spectra recorded on high and low radon days to estimate a radon spectrum, from which the coefficients are derived. 

The tool sorts the test lines by the uranium window count in order to split the lines into high-radon and low-radon groups, with 50% of the spectra in each group. The radon spectrum is calculated as the difference between the mean spectrum of the high-radon group and the mean spectrum in the low-radon group. The quality of the radon spectrum can be improved by carefully selecting the test lines to be included in the calibration. This can be done by selecting a set of test lines where there are large variations in the U window countrates. Then select an equal number of low-radon and high-radon lines for the calibration.

Use either Intrepid or Oasis Montaj to set up all the input database fields required by the tool. You will see which fields are required at Step 3 below. Of course, for an Intrepid database, the line number, flight number and fiducial fields must also always be present in the database – with prescribed names as indicated in the "Preparing The Database" section.

Processing Steps

    1. Open a database from the Main Window – File|Open. For the demonstration dataset select "demo_data\airborne_spectrometry\radon_stripping_testlines\RADON_STRIPPING_TESTLINES..DIR" (or the Oasis Montaj equivalent).
    2. Launch the tool – Calibration|Radon Stripping – Test-Lines.
    3. Set the database aliases and tool parameters – File|Set Aliases and Parameters. Click the Load From File button and select the "aliases_and_params_radon_strip_testlines.pc" control file from the working directory. For an explanation of the aliases and parameters click the Help button. Click Save And Return.
    4. Click the Calculate button to estimate the c1 coefficient. On completion, the tool displays the TC, K and Th radon stripping coefficients, the c1 coefficient and the upward-detector au coefficient (if the upward-detector option was selected in the Set Aliases And Parameters window) .
    5. View the log file – File|View User Log File to see the full results.