Background Removal

Use the Background Removal option (Geosoft.uxo.gxnet.dll(Geosoft.GX.UXO.UxoRemoveBackground;Run)*) to filter the magnetic sensor data to approximate the effects of the regional or background fields. This can be done using any combination of non-linear, rolling statistics, b-spline, and low-pass filters. An optional residual or background-removed channel can be added to your database.

ClosedExpand to see the locations (menus) where this option is available.

UXO Marine extension:

  • UXO-Marine Grad > Data Corrections
  • UXO-Marine Mag > Data Corrections

Fit/Remove Background Field from Mag Channels dialog options

Input channel(s)

Select one or more magnetic data channels to remove the background field from. At least one channel must be selected.

Script Parameter: UXO_REMOVE_BACKGROUND.INPUT_CHANNELS

Output channel suffix

Specify the suffix that will be appended to the output channel names. For example, if the input channel is "MAG" and the suffix entered is "resid", the output channel name will be "MAG_resid".

The number of displayed decimal places in the output channel(s) is the same as the number of decimal places in the input channel(s).

Script Parameter: UXO_REMOVE_BACKGROUND.OUTPUT_CHANNEL_SUFFIX

Filter #
(from 1 to 10)

 

Select the filter name to apply. You need to select the first filter; the remaining ones are optional. You will be prompted for additional parameters according to each filter’s requirements. Parameters for each filter can be adjusted by entering the values directly in the parameter fields.

You can apply up to ten filters at once.

Script Parameter: UXO_REMOVE_BACKGROUND.FILTER#

Script Parameter: UXO_REMOVE_BACKGROUND.FILTER#_PARAMETERS

[Clear Filters]

Click the Clear Filters button to remove your current selection of filters and parameters. All the Filter fields will be reset to their initial state.

[Save Filters]

Once you selected the filters and defined their parameters, you may want to save your filter configuration to a file. You can then use this file, when running the tool again, to automatically populate the Filter fields with your previously saved configuration.

Click on the Save Filters button to save the current filter definition to a configuration file (*.ini).

[Load Filters]

If you have a saved filter configuration (*.ini file), click the Load Filters button to open the browse dialog and locate the file. Select the file and click on [Open] to close the browse dialog and populate the Filter fields with the configuration parameters from the selected file. You can make further modifications to the filter definition, and you can save your changes to a new or existing configuration file.

Subtract background from input channel(s)

Select to subtract the final filtered output channel(s) from the input channel(s) to create a residual channel.

Script Parameter: UXO_REMOVE_BACKGROUND.SUBTRACT_BACKGROUND


Available Filters

Non-Linear

Max anomaly width

Specify the maximum anomaly width to be used by the non-linear filter calculations.

Tolerance

Specify the tolerance to be used by the non-linear filter calculations. Features greater than the tolerance are removed.

Rolling Statistics

Statistic to calculate

Select the required statistic from the dropdown list.

Window width

Specify the width of the rolling window. If this value is even, it is increased by 1 to give a window that is symmetric about each data point.

Shrink window at ends

Select to shrink the window at the ends. If yes, the window shrinks near the ends so that it remains of equal size on both sides of the individual data points. This can eliminate edge effects.

B-Spline

Smoothness (0.0 to 1.0)

Specify the smoothness (0.0 to 1.0). This controls how well the splined line honours the data. A smoothness of 0.0 will honour the data exactly while a smoothness of 1.0 results in an almost linear interpolation.

Tension (0.0 to 1.0)

Specify the tension (0.0 to 1.0). This controls the amount of curvature in the interpolation in the vicinity of data points. A tension of 0.0 will result in a minimum curvature interpolation while a tension of 1.0 produces a piecewise linear interpolation.

Low-Pass

Cutoff wavelength (fiducials)

Specify the cutoff wavelength in fiducials. A low-pass filter smoothes the input data by the application of a convolution filter to the data. The filter is called 'low-pass' because it allow slow wavenumbers (low frequencies) to pass to the output channel.

Application Notes

*The GX tool will search in the "gx" folder. The GX.Net tools, however, are embedded in the Geosoft.uxo.gxnet.dll located in the bin folder. If running this GX interactively, bypassing the menu, first change the folder to point to the bin folder, then supply the GX.Net tool in the specified format.

Filter Parameters

Selecting a filter will select the filter method and the default parameters. Use the expand button () to see and edit the filter parameters, for example when re-running the GX.

Filter Script Parameters

Each filter can have up to ten parameters. They can be set using the UXO_REMOVE_BACKGROUND.FILTER[i]_PARAMETERS script parameter where [i] is the filter number.

Parameters for each filter are specified in a single semicolon (;) separated string. For example, if "Non-Linear" filter is selected as the 1st filter in the dialog, the script parameter UXO_REMOVE_BACKGROUND.FILTER1_PARAMETERS="50;0.5" can be used to set the maximum anomaly width to 50 and the tolerance to 0.5.