Tutorial 4: Height Attn Coeffs And Sensitivities Calibration

Database Setup

This tool is for estimating height attenuation coefficients and window sensitivities using data specifically acquired for this purpose. Spectra (lines) are acquired at various heights over the calibration range – typically between 40 m and 200 m. Each line over the calibration range has an associated background line that was flown at the same height over water nearby. The background-corrected window counts are fit to the acquisition heights using an exponential regressions to estimate height attenuation coefficients. Sensitivities are derived by comparing the fully-corrected window counts to the known concentrations of the calibration range.

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\attn_coeffs_and_sensitivities\CALIBRATION_RANGE..DIR" (or the Oasis Montaj equivalent).
    2. Launch the tool – Calibration| Calibration Range.
    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_calrange.pc" control file from the working directory. For an explanation of the aliases and parameters click the Help button. Click Save And Return.
    4. Select the calibration lines from the database. Do this by selecting each of the Select buttons next to the Calibration Range Line Select textBoxes. Click the file icon next to the top-most Calibration Range Line Select textBox and select line 60. Repeat for lines 90, 120, 150, 180, 210, and 240.


Tool Tip:  You can use the following shortcut to select lines: The top Calibration Range Line Select button has the focus (after setting aliases and parameters), so pressing Done on the keyboard brings up the Line Select window. Select the line with the mouse, then press Done on the keyboard to exit the window. Now the second Line Select button will have the focus, so repeat for each line.


    1. Select the background lines from the database. Do this by selecting each of the Select buttons next to the Background Line Select textBoxes. Click the file icon next to the top-most Background Line Select textBox and select line 9060. Repeat for lines 9090, 9120, 9150, 9180, 9210, and 9240. You can use the same Tool Tip shortcut described above after manually giving the top Background Line Select button the focus using the mouse. The Include checkBoxes indicate that all lines will be included in the regression analysis.
    2. Click the Calculate button to do the regressions and calculate the sensitivities. 
    3. Toggle through the regression plots by checking the appropriate checkBox for TC, K, U and Th.
    4. The U attenuation coefficient is far too low, and the regression for this window is completely up the creek! The problem seems to be the two highest altitude lines (lines 210 and 240).
    5. Exclude lines 210 and 240 by unchecking all the checkBoxes next to these two lines. Click Calculate to run the regressions again. That looks better.
    6. View the log file – File|View User Log File to see the full results.
    7. Click Save to save the calibration constants to a file in a form suitable for cutting/pasting into a control file for airborne processing. Note that the sensitivities are for a particular nominal survey height – so select the appropriate sensitivities for your survey.