Tutorial 11: Topographic Correction

Database and Grid Setup

The Topographic Correction tool requires a database containing the final potassium, uranium and thorium radioelement concentrations to be corrected, as well as a Digital Elevation Model grid in ERMapper format. Additional ancillary fields required for the topographic correction are altimeter, temperature, pressure, easting and northing. The DEM grid should extend beyond the limits of the line data, and share the same projection/datum coordinate system as the eastings/northings. GammaSpec does not check that the coordinate systems are the same!

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\topographic_correction\TOPO_CORRECTION..DIR" (or the Oasis Montaj equivalent).
    2. Launch the tool – Enhancements|Topographic Correction.
    3. Set the database aliases and parameters – File|Set Aliases and Parameters. Click the Load From File button and select the "aliases_and_params_topo_corrn.pc" control file from the working directory. For an explanation of the aliases click the Help button. Make sure that the DIgital Elevation Model parameter is set to the full path to the DEM grid in "demo_data\airborne_spectrometry\topographic_correction\GRIDS". Click Save And Return. The digital elevation model should display in the left-hand panel window. By default, the potassium concentrations will display as the flight path map in the right-hand panel window. 
    4. Initiate the topographic correction. Select Run from the Run menu. On completion, the potassium correction factors will display in the right-hand panel window.
    5. View the log file – File|View User Log File to see the full results.