Topographic Correction
The Topographic Correction tool corrects fully-processed radioelement data (K, U and Th concentration estimates) for deviations in the topography from a flat-earth model. Output from the tool is topographically-corrected K, U and Th elemental concentrations, as well as the correction factors along the line for each estimate of K, U and Th.
The method is an enhancement of the method of Schwarz et al. (1992) for correcting airborne gamma-ray spectrometric line data for terrain effects. The correction is applied on a point-by-point basis to the line data. The correction is a scaling of the data by a factor that is the ratio between the counts that would be observed at the observation point (for unit concentration of the radioelement) over a 3D topography, with that over a flat-earth topography at the observation height. The method is based on the assumption that, for each observation point, there is a uniform concentration of the radioelements within the field of view of the spectrometer.
The correction needs to be applied before the data are corrected for aircraft height. So the Topographic Correction tool first "un-corrects" the final K, U and Th estimates for sensitivities and height. The topographic correction is then applied, and the height and sensitivity corrections are then re-applied.
To use this tool:
- Set the aliases and parameters – File|Set Aliases and Parameters. On exiting the aliases and parameters window, the tool will display the DEM in the left panel and a flight path map of Potassium in the right panel.
- Click Run to run the tool.
- View the log file – File|View User Log File to see the results.
Tool Tip: After re-sizing the window, you have to click the Update button to re-draw the DEM and flight path.
Quick Link: Descriptions of the aliases and parameters used by this tool can be found in the topographic correction aliases and parameters example control file.
See Tutorial 10: Topographic Correction for a tutorial on the use of this tool.
Reference
Schwarz, Klingele and Rybach, 1992. How to handle rugged topography in airborne gamma-ray spectrometry surveys. First Break, 10(1), 11-17.