Quick Start Guide to Magnetometer Data Processing

This guide will show you how to import and process magnetometer data in SonarWiz.

The procedure we outline will reduce diurnal and heading variations in the data, remove layback offsets, and produce a total and analytical field map.

The next step is to mark magnetic anomalies in the data and compare the anomalies to sonar data to try and correlate the anomaly to a known source.

Finally, run reports, listing out the position, depth, tow fish altitude and other metadata about your project for each anomaly.

By following this procedure, you’ll learn how to:

• Import magnetometer data into SonarWiz

• Apply cable out to navigation

• Filter and edit your raw magnetometer data

• Identify, mark and report on magnetic anomalies

• Grid and contour the total and analytic magnetic fields

• Display your data in 3D

For more information about the individual commands, please refer to the User Guide found in the Help Menu of SonarWiz. You can download a PDF version of this guide here.

Create a Project and Import Magnetometer Data:

1. Select the Create a New Project option in the Quick Access Toolbar.

Open

2. Enter a Project Name and then set the Approximate Project Position as shown:

Latitude: 21° 21.00000' N
Longitude: 157° 58.00000' W

Open

Click the Automatically Select CRS button. You should see that SonarWiz has selected EPSG:32604 (UTM Zone 4 North) as the coordinate system for this project.

3. Once the project is created, navigate to the Post Processing tab and Click the Import button to open the Import Dialog

On the Import dialog, check Magnetometer and click the Options button to open the Magnetometer Setting panel:

On the settings panel, select the File Template that matches your data. (GEMS Gradiometer for the example data used here).

Select the file to import and click the Import button.

4. Once the data is imported into the project, you will see files added to the Project Explorer as well as navigation track lines in the main display.

You can adjust the main display magnetometer file drawing options in the Preferences and Settings window located in the Quick Access Toolbar in the top-left of the program.

In the Magnetometer Options section, you will see options including labels, event numbers, drawing anomalies, as well as toggling between the imported lines displaying as Navigation Track Lines or Color Coded Amplitude Segments with options to change the color palette displayed.

5. To view the imported magnetometer data in each line, right click the file in the Project Explorer and select Edit Selected Mag File… (or hotkey select and ENTER)

The magnetometer file editor displays the data in a graph view with cursor tracked data values in the Info at Cursor and the records displayed on the X axis and the gamma on the Y axis.

The Graph Toolbar has options to zoom in/ out of the graph, measure, move from file to file, and add map correction points. For more information, see the Map Corrections for Magnetometer page.

There are 4 trace drawing options in the graph view:

• Raw Trace which displays the raw magnetometer data from the file.

• Smoothed Trace which will smooth the raw data based on the Ambient Smoothing Constant.

• Ambient Trace which will attempt to find the ambient background magnetometer signal based on the Observed Smoothing Constant.

These 3 drawing options can be used together in the Graph View together. The remaining drawing method, the Residual Trace, is calculated by subtracting the Smoothed Trace from the Ambient Trace. This option can only be displayed by itself in the graph view.

6. Many of the options for Magnetometer files can be accessed in the Magnetometer File Manager. To access the file manager, right-click Magnetometer Files in the Project Explorer and select File Manager…

The Make Like Selected option works similarly to the Make Others Like This option for sonar files and is used to copy adjusted settings from the selected magnetometer file to others in the project.

Currently only a horse and cart static offset is available as a layback option for magnetometer files and can be done by adding or offsetting the Cable Out value. The Info at Cursor in the File Editor will show the current Cable Out value added in each record. To adjust the layback for each magnetometer file, use the Layback Pct drop down menu (to apply all of the Cable Out value, select 100 pct).

The Export option in the Magnetometer File Manager is used to export the raw magnetometer data to a CSV file which can be gridded or brought into another program.

7. Anomalies (contacts for magnetometer files) can be captured on the imported files by either manually selecting them in the graph view using the Add Anomaly command or having SonarWiz automatically detect them using the Auto Detect Anomalies command.

To manually select an anomaly location, hit Add Anomaly and select the area in the graph view you would like to capture. Once the anomaly is created, the Anomaly Editor window will appear which will display the info a cursor as well as fields for adding text. If you have added a polygon SHP file to the project, the Cause of Anomaly section will allow you to select one of the attributes as a Known Cause.

The Auto Detect Anomalies command uses the Auto Detect Threshold value = X and scans the file for any samples where Smoothed Trace - Residual Trace > X. Each captured anomaly will appear in the Anomaly Management window and can be selected, edited, or deleted.

The user can either manually change the name of the captured anomalies upon creation or use one of the available naming schemes. To change the naming scheme for future captured anomalies, open the Preferences and Settings window, navigate to the Magnetometer Options section, and choose a User Specified Root Name and starting/ incrementing number in the Anomaly Naming section.

8. To export the captured anomalies and their data, the user can either create a .CSV or a report similar to the contact report.

To export a .CSV, right click the desired anomalies and select Export Selected Anomalies. This should open Windows Explorer where the user can select which output format is desired and if only certain types of anomalies are exported.

To create a Anomaly Report, right click the desired anomalies and select Report Selected Anomalies. Anomaly reports currently support 3 options:

• PDF

• MS Excel Table

• MS Excel Table w/ Mag Charts

9. To Grid the magnetometer data in the project, right click Grids in the Project Explorer and select Create New Grid…

In the gridder, choose either CMF Magnetometer Residual or CMF Magnetometer Raw for the Grid Surface Type and choose the desired Grid Algorithm. If you require interpolation between track lines use Natural Neighbor, it makes smooth contours between widely spaced lines. Finally, select a Grid Cell Size to about 1/10th the width of your line spacing. and Output Name and hit OK.

10. To make a contour plot of the grid. Right-Click the grid and select the Contour Grid… command.

Set a suitable Contour Interval and select the output Contour file type. Click OK. The contour plot will be added to the map as an overlay.