This How-to describes the use of the Wobble Analysis Tool to test for and correct common motion and offset related problems
On this page:
Setting up the data and activating the Wobble Analysis Tool
- Ensure you have loaded Raw Sonar Files into your project. These can be added using the 'Source' pull-down menu (1) at the top of the main window.
- It's best to build a dynamic surface. Select one or more of the sonar files from within the Project Sources window (2). This window can be toggled in the 'Window' pull-down menu (3).
Choose the same line that will be used in the wobble test. Select 'Create Dynamic Surface' from the 'Dynamic Surface' pull-down menu (4) or click the 'Create Dynamic Surface' Icon (5).
- Select a single line to be loaded into the wobble test tool from within the Project Sources window (2).
Wobble Test window overview
The Wobble Test requires interaction in two areas of the Qimera software.
- A selection box will be placed over the data in the geographic window. It can be moved, resized and rotated using the nodes on the box itself.
The white arrow indicates which direction the soundings will be viewed in the point cloud display within the Wobble Test window.
- The Wobble Test window will pop up once the tool is initialized as described above.
- The Wobble Test window can be divided into 3 main areas, arranged vertically.
- At the top is the cross sectional point cloud. This contains the soundings that fall inside the selection box that is located over the grid in the geographic window. The points are viewed from the side in the direction of the white arrow on the selection box.
- In the middle is the Multibeam Options section. It allows for toggling the reversal of common MBES setup options and relative directions.
- The bottom section allows for toggling the reversal of the direction in which Roll, Pitch, and Heave are applied. It also contains sliders allowing for adjustment of Motion Latency as well as Along Track, Across Track, and Upward positional offsets of the IMU relative to the vessel CoG.
Using the Wobble Test Tool
In the example used here, there is a wobble that doesn't exist at nadir and gets more pronounced towards the outer beams.
- Move the selection box (1) towards the outer beams and ensure that it is aligned parallel to the ship track.
- Note the change in the point cloud (2) in the Wobble Test window. The point cloud will be adjusted in real-time as you toggle settings and move sliders in the Wobble Test window.
- As an exercise, you can cycle through the check boxes, toggling their application. If a certain setting doesn't improve the problem or makes it worse, return the setting to it's original.
- To reset all the settings, click the Reset button (3) at the top of the Wobble Test window.
In this example, the only change that improved the data was the motion latency. By moving the slider and observing the change you can zero in on a setting that provides the best reduction in the motion artifact.
Certain situations may require a combination of adjustments, namely when an IMU is not providing correct lever arm reductions and these were not applied anywhere else.
- If the scale of the slider needs to be adjusted, it can be done by clicking on the Settings button (4) that is located to the right of each slider.
- Each slider also has a Reset button (5)
Saving and Applying Changes
- Once you are happy with your adjustments, you must click on the Save Edits button (1) at the top of the Wobble Test window. This will prompt you to save a wobble test file. Rename and save the file in your project.
- Now that you have saved the edits, the 'Apply' button (2) at the bottom of the Wobble Test window is active. Clicking this will bring up a dialog box where you can select when the changes will start to be applied to the data.
- Select the starting file for the edit application and click OK
- A bar will appear at the top of the geographic window (1) prompting you to reprocess the affected files. Ignore the box for now or click no.
- Notice that the reprocess icon (2) appeared next to one or more line names in the Project Sources box.
- If you hold your mouse over this icon it will describe what reprocessing steps will be carried out.
- A single line can be reprocessed by double clicking on its file name in the Project Sources box.
- To reprocess all lines that require update, click on the Auto Process icon (3) near the top menu bar.
- Once the reprocessing is complete, the Dynamic Surface(s) will be recomputed.