Chesapeake SonarWiz--Quick Start Guide to Side Scan Data Processing

Chesapeake SonarWiz--Quick Start Guide to Side Scan Data Processing

This guide will show you how to import and process sub-bottom data in SonarWiz

By following this procedure, you will learn how to:

Import sidescan data into SonarWiz

Smooth and interpolate navigation

Apply laybacks and sheave offsets

Apply gains such as TVG and EGN

Adjust and trim data

Create mosaic maps of the survey

Instructions

1. Click the New Project Icon to open the Create New Project Dialog

2. Enter a Project name and Project Folder, then set the approximate position of the data. This can be done either by entering in a known location or Get from File – navigate to a single file from the project (note: at this point, only one file is needed to set the geodesy, regardless of the number to be processed). Then, click the Automatically Select CRS button.

In the program, go to the second tab – Post Processing and click Import

4. Set the Import Geodesy of your raw files. The navigation in these files is stored using geodetic coordinates (latitude and longitude) on WGS 84. The Spatial Reference ID (SRID) for this system is EPSG:4326. You can use the Choose… button to select the Project geodetic coordinates and SonarWiz will select the corresponding EPSG code for you.

5. Select data files to use. Multiple files can be selected at once.

6. Check Side Scan Sonar to import the sidescan data. Click the Options button next to Side Scan Sonar to set the import channel and import Samples Per Channel settings (the defaults work fine).

7.  Click OK to import the sidescan data.

8. Open the Color Window by clicking on the Color Window icon in the Mapping Toolbar. Use the Datatype dropdown to pick the sidescan channel you just imported and then adjust the color palette until your data shows up clearly.

9. To apply navigation smoothing and interpolation, select the SSS line in the Project Explorer and look in the General tab of the Properties window. Scroll down to the section called Projection and Smoothing. Set the Project data using to Sensor heading or course made good. Set the time constant for course smoothing to match your ping rate to start. Increase the value if your navigation is still jumping around. NOTE: a time constant value of 0 pings turns off smoothing and interpolation.

10. To apply Sheave Offsets and Laybacks, select the SSS line in the Project Explorer and look in the General tab of the Properties window. Scroll down to the section called Layback. Check Enabled to apply laybacks. For algorithm pick: Cable - Percent and then use the slider to set the Cable out percent to 100%. You can also apply Sheave offsets from your navigation system to the sheave (tow point or pole mount).

11. Open the Bottom Track display by Right Clicking on a file and select the Bottom and Far Field Track command from the Context Menu. This can also be done by Double Clicking on a file in Map View.

In the Tracking tab, Click the Clear button to remove the existing bottom track. You may need to expand the window to see the labels on the controls.

Track: Bottom
Channel: Port (or Starboard)
Algorithm: Threshold Detection
Blanking: 5
Duration: 14

Threshold: 3

Click the Track All button to track the bottom. You may need to experiment with the Threshold and Duration values to get a better track. You can also use the Insert Points and Remove Points buttons to manually track the bottom with the mouse.

In the toolbar, Save your work, then use the green Next and Previous arrows to work through the remaining lines in your survey.

12. To apply gains, open the Settings window by Right Clicking 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.

Click Enable UGC and select TVG Mode. Set the Salinity to 35 psu and click the Auto Fill TVG button to compute the absorption coefficient for your sonar frequency. Click Apply.

Here is Time Varying Gain applied to a file:

13. Another good gain algorithm is EGN. Uncheck Enable UGC (if applied) and Check Enable EGN. Click the Rebuild EGN table, give the table a name, click the Start button to build the table. When the table is finished, Select the table in the EGN drop down box.

Here are the results of using EGN:

14. To adjust the display range of sonar data. Go to the Display tab in the File Properties Window and at the bottom you will find the Displayed Range options. The Specified Range option will allow you to input for Port and Starboard (see below).

15. 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 from one file to the rest of your project.

Right-Click the reference sonar file and select Make Others Like This… from the context menu. Select the settings you would like to copy, then pick one or more files to adjust. Click OK to copy the settings.

16. 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 Post Processing > Exports > Save Project As Geo Image… command.

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):