How-to Side Scan Sonar
This document describes how to interface, use and process data from Sidescan Sonar systems.
Sidescan Sonar (SSS) is a device that measures the intensity of the reflections from the seabed or objects on the seabed. SSS is usually towed approximately 10% of the sonar operating range elevation above the seabed.
There are also multibeam echosounders capable of outputting data in two channel SSS format or singlebeam echosounders that have a SSS add-on.
A SSS can be operated from another object (tow fish) or it can be mounted on the survey vessel or an underwater vehicle (ROV/AUV).
On this page:
In short the workflow is as follows:
- Add the Sidescan Sonar as a system to your setup.
Possibly a depth recorder and an altitude determining system need to be added as well when the sidescan sonar will be towed behind your vessel.
This then also requires a layback definition.
Activate the available systems.
Activate the correct sounding grid and DTM files to record the data.
The raw sonar data packets are stored in *.db files and the vessel and footprint positioning data are stored in *.qpd files.
Set up the Sidescan Image Display to view the data while recording.
Load the data into the Processing Manager and use the Sidescan Viewer tool to review the data.
Create a database of targets found with the Sidescan Viewer and use the Target Viewer to view and edit the targets. (See bottom of page.)
Setting up a SSS system in Database Setup
Create a New System in Database Setup on the object on which the SSS is installed:
The second page contains the General parameters:
The third page contains the Channel parameters:
Using the Channel Properties, set the appropriate Transducer, Orientation and Offsets. The other items are administrative (not used by QINSy for computations or data correction).
|Sidescan Sonar Channel Setup|
|Sidescan Channel(s)||Use the Add button to add the Sidescan Channel(s).|
Node at which the transducer or channel is located.
|Orientation||Direction to which the transducer is transmitting/receiving.|
|Slot ID||Depending upon the selected SSS interface driver, some require the SLOT ID to be entered to allow QINSy to decode multiple channels of SSS data. |
An example is a dual frequency SSS unit providing 4 channels of data (2 channels per frequency). Refer to the QINSy Drivers and Interfacing manual for further details.
The Slot ID is not used for local area network ID.
The GUI is sensitive to the chosen device driver - in the case only two channels are available, no SLOT is shown.
|Roll, Pitch, Heading offsets|
Mounting angles of transducers (same as with Multibeam systems). Note that roll value is ignored since Sidescan is by nature indifferent to roll.
|Frequency (kHz)||Nominal transmitting frequency.|
|Number of beams|
Always set this to 1 except when using a Multibeam Sidescan sonar system like Klein 5000 Series.
|Horizontal beam width||Opening angle of transducer in horizontal direction (usually 1-2°).|
|Vertical beam width||Opening angle of transducer in vertical direction (usually 40-60 °).|
|Vertical tilt angle||Angle between horizontal axis and center beam limits (see figure above).|
EXAMPLE RESON SeaBat 71xx MBES and Backscatter
EXAMPLE KLEIN dual freq SSS (4 channels, 2 on each frequency)
Pressing “Finish” will close the setup of the System and will save the changes.
A new Sidescan system appears in the tree view below the Object, see figure below.
A glossary of the properties of either system or individual channel can be viewed in the right pane of Database Setup when a tree item is selected.
After completing the Setup, the system can go online.
Here the settings need to be entered in order to control the data that is coming in and to control the storage.
The Processing Manager and the Sidescan Viewer rely on the positions/altitudes of the sidescan sonar that are stored in the QPD so make sure that QPD’s are created and that the sidescan sonar is enabled in Computation Setup and Session Setup.
Furthermore the SSS image can be displayed in various displays.
The parameters of the SSS can be accessed via the Computation Setup:
Make sure the Sidescan system is enabled in the Computation Setup.
Note: the beam is now located lower than the flat seabed assumption. The radial distance is rotated to previous seabed displayed by the sounding grid.
To locate the derived position from a beam, an assumption has to be made about the seabed.
Sounding Grid Reference
The elevation of the Sonar head is crucial in this assumption; an external observation is needed and only with RTK mode or tide corrected data a good result will be achieved.
This can be done in Replay mode if tide data is not available online.
|Altitude||The geo referencing of Sidescan data requires a proper altitude of the Sidescan fish above the seabed. |
The altitude is used to slant range correct the recorded data.
The altitude source can be an External Observation system, e.g. an echo sounder or sensor in the fish:
Or a fixed user defined value:
Or from a Bottom Tracking Algorithm.
The algorithm will start searching at the sample represented by the search Start Range and searches up to the sample that is represented by the search End Range.
|Bottom Track Algorithm|
|Parameters||Bottom Track parameters can be entered in the Controller (here) and in the Sidescan Display-Select-General (“Use Filter Settings from Controller option” disabled).|
The Bottom Track Algorithm will start searching the samples for the bottom at this range.
The Bottom Track Algorithm will stop searching the samples for the bottom at this range.
|Channel||If for any reason one of the channels is not working properly, or for instance there is a jetty on one side and you want to exclude the channel from the algorithm then you can make a choice which of the channels will be used to calculate the seabed.|
The threshold value can either be fixed or recomputed for every ping (relative).
The different settings are described below:
The user can define a threshold value.
Method: Absolute Threshold
The threshold is re-determined for every new Sidescan ping. The Mean value for the entire channel is computed.
Method: Relative to Mean Value
The threshold is re-determined for every new Sidescan ping. The Peak (maximum) value for the entire channel is computed.
Method: Relative to Peak Value
Example Klein 2000
Dynamic (continuous updating) means normalization is switched on.
The signal from the SSS can experience some noise. The normalization mode (see figure above) removes noise by averaging a certain number of swaths (buffer size) in the buffer.
|Footprint Count||This feature sets the number of virtual footprints. For these footprints an Easting and Northing are created and they will be stored in the sounding grid.|
Make sure this number of footprint count enables a good topography of the bottom.
Channels can be turned on or off in the Computation Setup, this means that they will not be stored in the QPD or the sounding grid, but they will be stored in the database.
The SSS data can be stored in a specific Sidescan data layer in the Sounding Grid for further processing. (Storage-Sounding Grid)
The position and altitude of the SSS data can be stored in a QPD so that it can be loaded with the corresponding recorded database in the Sidescan Viewer tool. (Storage - DTM)
The storage of the sidescan data is done through Session Setup.
Go to “Settings” on the menu bar and select “Session Setup”, the following dialog will appear:
Session Setup - Sounding Grid
Go to the Storage menu and select “Sounding Grid"
- In the Sounding Grid menu select a grid using the browse button [ ... ]
- For each System the Layer needs to be specified. (Use the button 'Add Extra Layers' when necessary.)
You may want to create a new grid to store the SSS data in.
Carry out the following steps to accomplish this:
Select 'New' and the following dialog will appear:
- Enter a file name and enter a base cell size.
The size is dependent on the footprint count (see Channels): the higher the footprint count the smaller the cell sizes that can be used.
- Select whether the origin of the grid must be generated automatically or that it must be specified by a grid Easting and Northing.
- Select the unit type.
- Select one of the layers from the lower pane and click on the Layer Type to select the correct one.
The Icon will be adjusted automatically.
- Click on the Attribute Selection and select which attributes to show.
The more attributes are selected, the larger the sounding grid will be.
Session Setup - DTM File
In “DTM File” the format must be set to *.qpd. This will create result files which in combination with the raw database can be viewed in the Sidescan Viewer.
- DTM Format should be set to *.qpd
- Make sure the Sidescan System is enabled.
The Altitudes (e.g. from the bottom track algorithm or external observation) of the sidescan fish channels are stored in the QPD.
These can be visualized and edited in the Sidescan Viewer.
Sidescan Image Display
The Sidescan Image Display displays the conventional sidescan image digitally (see figure below).
It displays the intensity of reflections from the seabed.
During recording the gain can be adjusted using the
Press the "G" for Automatic Gain, or press the + or - buttons repeatedly for manual adjusting.
In this window the system and the used frequency can be selected for display in the Sidescan Image Display.
The settings which can be selected are those which are defined in the Database setup.
The Settings for Altitude and Filter can be changed in the Controller-Computation Setup.
To change these settings in this window, remove the tick and the window will show two more tabs for these items.
The settings from this menu will not be automatically copied to the Controller so either use this menu or the Controller but do not mix them.
The default storage location for targets is the Target Database.qgfanno file in the Project\Annotations folder, but when the option “Use alternative database” is selected a different line database can be used.
The targets will be automatically labelled with a prefix name and number.
To save the targets' screen captures as bitmaps select “Save screen capture of target”.
Select “Options” to open the Target image options dialog where the storage options can be set (see figure below).
Target Image options
The target images are by default stored in the Project\Graphics folder.
During recording save a target as follows:
- Go to “View” on the menu bar and select “Mouse Mode”
- Select “Create New Targets” or select New Targets from the toolbar.
Because the SSS data can be stored in a sounding grid the sounding grid with SSS data can be displayed in the Navigation Display.
In order to display a sounding grid in the Navigation Display one must be selected in Session Setup (see figure Session Setup).
In the View Properties select the correct Layer and the Attribute. QINSy contains a specific Sidescan Copper color map that can be used to display the SSS data.
SSS Gradient Colors (without shade layer)
SSS Gradient & Sun (with shade layer)
The first figure shows a normal Sidescan image; the second figure is a combined image of Sidescan sonar data and a DTM surface (for example multibeam data), providing more contrast.
3D Grid Display
The 3D Grid Display is also able to display SSS data in combination with a DTM surface (for instance multibeam data).
To enable this option set "Layer" from the "Color source settings" pane to a layer that contains Sidescan sonar data or magneto meter data and select which attribute of the layer to show.
To display differences between two grids a Reference layer can be used. Select the layer's attribute and the Combination mode.
An example of a combination of SSS data and a DTM surface in the 3D Grid Display is shown in the figure below.
SSS data in combination with a DTM surface
As mentioned before the SSS data will be stored in QPD files and in a Sounding Grid file.
Start the Processing Manager to be able to edit the Sidescan data.
- In the Project Explorer, right-click on Survey Files
- Select Import
- Select Survey
A regular Windows dialog will open where you can select the sidescan *.qpd file(s).
If you don't see the survey line(s) in the Plan View after pressing 'Open', press the Zoom to Fit button
Launching the Viewer
- In the Project Explorer, select a QPD file that contains the track of the object on which the SSS is located, the SSS data is read from the corresponding DB file.
- Press Edit in the Processing ribbon tab to access the processing tools.
- Click on the Sidescan Viewer icon.
Multiple Sidescan Viewers can run at the same time as long as different files are selected.
The Sidescan Viewer shows raw SSS data in combination with result data.
The Sidescan Viewer is accessible either from the QINSy Console via Replay, or from the Processing Manager via the Processing Ribbon Tab.
The latter has the advantage that the view port extents are visible in the Plan View:
Viewport as visible in Processing Manager
The SSS data can look as follows:
The Sidescan Viewer has almost the same options as the Sidescan Image Display, but because it is a processing tool there are some extra options:
In the Sidescan Viewer it is possible to use normalization. With this option it is possible to calculate and to apply a gain curve for each channel from the average intensity of both channels.
Before normalization the altitude must be applied correctly by a fixed value, an external device or with the Bottom Track Algorithm.
The altitude settings are the same as used online (see Altitude).
To use normalization carry out the following steps:
- Go to “View” on the menu bar and select “Normalization Settings”.
- Select the tab “Normalization”, the following dialog will appear:
- Select “Enable Normalization”. Select “New” in order to calculate new gain curves.
- In the appearing dialog select “Next” to continue.
- Select whether the normalization must be applied to all swaths or only the visible swaths.
Select “Next” to continue, the following dialog will appear:
Average channel intensity
In the histogram displayed in the figure above the intensity and average of each channel are displayed, as well as a combined average.
With this data gain curves will be calculated for each channel.
The normalization module will automatically calculate a “Normalization target Level”. This can be adjusted manually if necessary.
- Select “Next” to continue, the following dialog will appear:
The histogram displayed in the figure above shows the calculated gain curves for each channel.
- To save the gain curves to a file press the Browse button [ ... ] and specify a path.
These gain curves can also be used for other SSS data that is viewed in the Sidescan Viewer.
These files must then be selected in the “Normalization” tab of the “View Properties”.
In the Sidescan Viewer it is possible to save targets from the Sidescan image to bitmap or geotiff images.
Both image formats can be saved as geo referenced images.
This means that the created image will have the correct coordinates of the target.
In order to create these images follow the next steps:
- Scroll to the position in the Sidescan image where the target is located.
- Go to “Select” on the menu bar and select “Target Selection”.
- Under the “Target Selection” tab, the following dialog will appear:
- Select a target database using the 'Browse' button.
If no previous database exists, use the 'New' button to create one.
- Select “Save screen capture of target” and press “Options”.
The following dialog will appear:
Target image options
- Select whether the image must be geo referenced and what kind of file format should be used. (Only *.tif files can be imported for display in the Processing Manager.)
By default the image files will be stored in the Graphics folder of the project.
- Select the minimum number of pixels and the mask color. The mask color is the color that will be used on places where there is no data.
In case of Sidescan colors there is a lot of white, so for more contrast it is better to choose another color than white.
- Text annotation can also be added to the image, select the items of interest and press “OK” to finish.
- Press “OK” to exit the “Target Selection”.
- Go to “View” on the menu bar and select “Mouse Mode”, and then “Create New Targets”.
- Click lines around the target and click on the right mouse button and select “Save Target”.
The following dialog will appear:
- As can be seen, the image will be saved with an Easting and Northing coordinate.
- The name of the image can be changed by typing in a new name.
A Classification name can be selected using the drop down menu. Classifications can be created in the Target Viewer tool, see below.
- The image will be saved in the Graphics folder of the project, the lines drawn around the target will be saved in the Annotations folder and the target data will be stored in the Support folder.
As mentioned in Online - Storage the Sounding Grid can be filled with SSS data.
Import the data into the Processing Manager to view it in the Plan View.
In the Project Explorer, right-click on Sounding Grids and select Import to select the recorded grid file.
SSS data in a sounding grid in the Processing Manager's Plan View
Because a layer is used especially for SSS data the color map can be set to “Sidescan Copper”. This can be altered in the “Grid tools” tab - Color Settings option.
Sidescan data is backscatter data, so there is no height information available.
To add shade for better contrast:
- Press 'Sun Illuminated' in the Grid tools tab - Edit menu.
- To adjust the Sun Illuminated settings go to the Color settings option
- Select Sounding Grid Settings
- Select the Render Options tab.
The shade can be adjusted by changing the “Azimuth” and the “Elevation” of the imaginary light source.
The SSS data can be exported to a Geo TIFF image for further use.
Follow the next steps in order to export the data to Geo TIFF:
- Right click in the View Plan and from the menu choose a selection option:
Select an area to be exported.
- Select "Export" from the Grid tools tab - Edit option. The following dialog will appear:
- Set the “File type” to “Geo Tiff" (*.tif & *.tfw).
- Select which type of data will be exported to Geo TIFF by selecting the SSS layer as the layer to export and set a detail level.
- Set the attribute to “Mean” depth.
The Geo TIFF images can be used in the Navigation Display or may be useful for other software programs.
For an overview of the saved targets they can be shown in the Plan View of the Processing Manager:
- Go to the Home ribbon tab
- Press Settings
- Activate the showing of targets and use the browse button [ ... ] to select the target database as created with the Sidescan Viewer.
When a target outline is clicked upon, the Cursor Info panel will show all the Target Info as stored in the Target Database:
In the Target Viewer various databases can be imported, viewed and edited.
In the Processing Manager, Ribbon Tab Home select 'Settings'.
Here you can set which database to view.
The outlines as created in the Sidescan Viewer will be shown in the Plan View as a visual aid.
Then select 'Target Viewer' to edit the database.
The coordinate shown in the lower right corner of the image panel is the coordinate of the top left corner of the stored image.
Press the option 'Enable Editing' to be able to adjust the Type Description / Description / Comment / Image File or the dimensions of the targets.
Press 'Classifications' to add images to the list of types of targets found in your project.