EM Noise Rejection

Use the EM Utilities > Reject Noise option (geogxnet.dll(Geosoft.GX.EM.NoiseRejection;Run)*) to remove noise from the EM decay arrays. You must first run the EM Noise Calculation option.

Noise Rejection dialog options

Input EM channel	Input array channel to filter. Only arrays with onboard time gates will be displayed. Script Parameters: REJECT_NOISE.INPUT
Output EM channel	Filtered EM channel. Script Parameters: REJECT_NOISE.OUTPUT
Line selection	Select which lines to apply noise rejection to. Script Parameters: REJECT_NOISE.LINE_SELECTION (S-Selected[default], A- All , D-Displayed)
Noise values	If you have run the EM Utilities > Corrections > Calculate Noise option to calculate the standard deviation for each gate, they will be loaded here. Otherwise, this entry is not populated. These values are also displayed in the table that follows beside the corresponding gate The values in this edit box reflect the standard deviation of each gate. You can edit these values here, and the table will be automatically updated.
Noise multiplier	The values displayed above, scaled by this multiplier define the noise threshold for each gate. Script Parameters: REJECT_NOISE. NOISE_MULTIPLIER
Show hidden windows	Array elements for which no data has been supplied will not be displayed initially. If you would like to see these elements, check this box. Script Parameters: REJECT_NOISE. SHOW_HIDDEN_ELEMENTS
[Import from File]	An alternative approach is to import the noise values from a .csv file. The CSV file must have a noise threshold for each valid element of the array. The EM array is then updated with the new threshold values.

Application Notes

The calculated standard deviation of each gate is saved in the registry of the array channel for further use.

Apply this tool with care. The noise rejection is an iterative process. You can start with the standard deviation of each gate as the noise threshold. After applying it, inspect the profile of each filtered gate to see if you have attenuated the noise adequately. If the noise threshold is incorrect, you may have accentuated the noise instead of attenuating it. Generally, one standard deviation will not be an optimum noise threshold for all the gates, and it will require adjustment. Once you have adjusted the noise for all the gates you can cut/paste from the “Noise values” window to a file and save it.

*The GX.NET tools are embedded in the geogxnet.dll file located in the "...\Geosoft\Desktop Applications \bin" folder. If running this GX interactively, bypassing the menu, first change the folder to point to the "bin" directory, then supply the GX.NET tool in the specified format. See the topic Run GX for more details on running a GX.NET interactively.