EM Noise Calculation

Use the EM Utilities > Calculate Noise option (geogxnet.dll(Geosoft.GX.EM.EMNoiseCalculation;Run)*) to calculate and save the standard deviation of each element of the array. Generally, the noise is estimated to be one standard deviation of a quiet segment of the EM array data.

EM Noise Calculation dialog options

Input EM channel	Input array channel to calculate the noise from. Only arrays with onboard time gates will be displayed.
Mask channel	Mask EM data using this channel before calculating the noise. Only channels of Class "MASK" are available in the drop-down list.
Data selection	Statistics will be calculated on the selected data range. The range options are: Selected lines, Displayed line, All lines. Furthermore if you highlight a segment of data before invoking this tool you will be offered an additional option, Marked rows. The standard deviation will be calculated on the selected data range.
Minimum noise	Set this level to the known instrument noise. Noise levels below this limit will be set to this limit.
[Calculate]	Click this button to update the noise calculation for the array elements (gates) of the selected channel and lines. The noise is set to one standard deviation for each array elements (gate).
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.
[Save]	Clicking on Save will prompt you for a csv file name to save the calculated noise in. See Application Notes for file format description.

Application Notes

The table in the dialog shows the indices of the array along with the time gates and the calculated noise level which is set to one standard deviation for each time gate. The only editable part of this table is the noise level. Double click on a cell to get into edit mode. When you click Save the current values of the table are saved to a csv file, but not into the array channel registry. You have to click OK to save the current noise values in the channel registry.

Noise File Format

The noise values are saved in a CSV file with the following format:

// Channel: Channel_name    <- The noise has been calculated on this channel

// Data selection:          <- See Data Selection

// Valid gates: 1st_valid_index-Last_valid_index    <- Specified by the user

Noise[_{1st valid index}], Noise[_{2nd valid index}],...., Noise[_{Last valid index}] <- Consecutive noise values

Data Selection

The following selections are supported:

Data Selection: Comma separated Selected lines  <- Selected lines

Data Selection: All lines                       <- All lines

Data Selection: Lnumber                         <- Displayed line

Data Selection: Lnumber,Fids:StartFid-EndFid    <- Marked rows

Sample File

// Channel: em_Z_final_off

// Data Selection: L1180.43, Fids: 57878-58845

// Valid gates: 14-45

0.0631,0.0483,0.0387,0.032,0.0269,0.0228.0.0193,0.0165,0.0141,0.0121,0.0103,0.00874,

0.00739,0.00622,0.00518,0.00433,0.00361,0.00296,0.0024,0.00195,0.00157,0.00125,

0.000981,0.000764,0.000601,0.000474,0.000365,0.000276,0.000209,0.000163,0.000131,0.000101

*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.