Sidescan Data Processing

This guide will show you step-by-step how to process side scan data in SonarWiz. For more information about the individual commands, please refer to the User Guide found in the Help Menu of SonarWiz.

Creating a Project

1. Create a New Project by clicking the '+' icon.

2. Enter a Project Name and then set the Approximate Project Position. This can be done either by entering in a known location or use the Get from File... button – navigate to a single file from the project and SonarWiz will extract the position of the project from the file.

For detailed instructions see Create a New Project.

Importing Sidescan Data

Sidescan data is imported into a SonarWiz project and converted from the native binary format into a SonarWiz CSF file. The import process is done from the Post Processing ribbon menu.

Open

To import side scan data:

1. In SonarWiz, go to the second tab – Post Processing > Import > Sidescan Files...

2. Select data files to import. Multiple files can be selected at once.

3. Select the Channels to Import on the Open dialog. Low frequency (Channel 1,2) or high frequency (Channel 3,4) must be imported separately.

4. Click the Advance Settings button to select the Import Samples per Channel. The default is 1024, but feel free to change it to the higher mode.

5. Click the Open button to load the data.

The sidescan data will be loaded in the program. The next few steps get the data adjusted with gains, bottom track and other tools to create a nice image.

Open

Apply Sheave Offsets and Laybacks

To properly compute the tow fish position behind the vessel or platform, SonarWiz needs to know the offset from the navigation receiver to the sheave (tow point) and we need to apply any recorded cable out values. This is done by modifying the line properties.

To apply sheave offsets:

1. Select the sidescan line.

2. In the Properties window, Select the General Tab.

3. Scroll down until you see the Layback section

4. Enter the X, Y and Z offsets from the navigation source to the sheave.

5. Check Enabled to apply
   
   

To apply cable out:

1. Select the sidescan line

2. In the Properties window, Select the General Tab

3. Scroll down until you see the Layback section

4. Select the Layback algorithm to: Cable - Percent.

5. Set the Cable out percent to: 100%.

6. Check Enabled to apply.

Bottom Tracking

To open the Bottom Track waterfall display, Right Click on a file and select the Bottom and Far Field Track command from the Context Menu.

To bottom track the file:

1. Select the Tracking tab in the Sidescan Analysis Window

2. Click the Clear button to remove existing tracking

3. Set the Track drop down to Bottom

4. Set the Channel drop down to either the Port or Starboard channel.

5. Set the Port (or Starboard) Blanking, Duration and Threshold.

6. Click the Track All button (change the settings and repeat steps 5 and 6 until you get a good track)

7. Click Save icon to save the track.

You may need to use the Manual Tracking buttons to clean up the bottom track with the mouse. When you are done, you can move to the next line by clicking the Next or Previous Arrow buttons.

Close the analysis window when you are finished tracking all of the files

Applying Gains

Most raw backscatter data requires some gain adjustment to compensate for intensity drop off associated with sound spreading and absorption. In SonarWiz, these algorithms are applied in the sidescan Settings menu.

To open the Settings window, Right Click on a file and select the Settings command from the Context Menu.

Try different gain settings to see which one makes the image look best. Here are two examples:

To apply Time Varying Gain (TVG) to a file:

1. Enable UGC check box

2. Click the TVG Mode button

3. Set the Salinity (35 psu is average ocean salinity)

4. Click the Auto Fill TVG button (this estimates the absorption coefficient)

5. Click Apply.

Here are the results:

To apply Empirical Gain Normalization (EGN) to a file:

1. Enable EGN check box

2. Click the Rebuild EGN Table...

3. Select the files to use in the table

4. Give the table a Name

5. Click Start to build the table

6. When the table is finished, Select the table you just built in the EGN drop down
   
   

Here are the results:

Make Others Like This

You can copy settings from a reference file into other files in your project using the Make Others Like This... command. This command is useful for setting gains, offsets and layback, and other settings that you want to copy.

To use the Make Others Like This command:

1. Right-Click the reference file and select the Make Others Like This…

2. Select the settings from the reference file that you want to copy. Use the Apply all settings check box to copy everything.

3. Select Files to Modify. Use the Check All box to modify all the files in the project.

4. Click OK to copy the settings

Create a Mosaic

SonarWiz mosaic export is What-You-See-Is-What-You-Get. Set up the map exactly how you want it to look (colors, graticule, map scale, etc). Then execute the Save Project As Geo Image command.

To Export the Map Mosaic as a GeoTiff:

1. Click on Post Processing > Export > Save Project As Geo Image...

2. Set the output Image File Name, File Type and Output Color Resolution

3. Specify the Image Resolution in meters/pixel.

4. Click OK.

NOTE: If you make the background transparent, this will add a band to the output image for the alpha (transparency) channel.

The information window in the dialog will show you the output image size based on your current settings. Exporting huge areas in high resolution is slow and may exceed the memory limits. See the Post Processing > Export > Save Mosaic as Tiles command for an alternative approach.

Your final image is output where you specified (defaults to the Project GeoTiff folder):

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