Quick Start Guide to Processing Forward Looking Sonar Data

Forward Looking Sonars (FLS) are designed for navigation and obstacle avoidance. However, near the seabed a portion of the sonar view ensonifies the seafloor and this data can be extracted by SonarWiz into a high-resolution mosaic. This Quick Guide will get you started processing FLS data in SonarWiz.

Instructions

1. Create a new project.

   Open

   

    

2. Enter a Project name and then set the 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

   Open

   

    

3. On the Post Processing ribbon, Click Import | Forward Looking Sonar Files…
   
   

    

4. In the Open dialog, Click the Advanced Settings… button and review the import settings.
   
   

   The Import Samples setting will control the across-track resolution of the imported imagery, the compression settings can be left at 16-bit scaled for most applications, or turn off compression by setting the compression to FLOAT for both raw and processed samples.

5. Select one of the FLS files in the viewer and then Click the Choose Sampling Area button to open the FLS Sample Area Chooser window.
   
   

    

6. In the FLS Sampling Area Chooser window, use the Frame Control buttons to advanced through the file and find a target that clearly shows the area of the FLS frame that is in focus on the seabed. In this example, I’ve played through to find a pipeline on the seabed:
   
   

   Note that the area at the center and forward of the image frame is probably in the best focus

7. The sampling window is drawn in green overtop of the FLS image frame. The sampling window defines the region of each FLS frame that will be extracted and assembled into the CSF file for mosaicing. Use the mouse to drag the edges of the green rectangle into a broad, narrow window. You can refine the position of the window by typing in the exact minimum and maximum values you want to use in the Sampling Window boxes to the left of the screen.
   
   
   

   
   We recommend experimenting with the width and height of the sampling window. The goal is to choose a portion of the FLS frame that has minimum distortion of the seabed. Each FLS frame will be clipped and extracted as a small image. Optimize the height of the sample window so there is a minimum of along-track overlap between the sample clips but sufficient height so that there are no along-track gaps between pings. It is helpful to advance (play) the FLS data frame by frame until features of interest are showing. These can help aid in choosing the optimal sampling window. Most notably they will show where the beams have the best focus and lowest distortion.

8. Click OK to close the FLS Sampling Area chooser.

9. In the open dialog set the number of frames to skip. It is usually not necessary to import every frame as AUVs and ROVs generally move slowly compared to the frame rate of the FLS and there is a lot overlap between frames.
   
   

    

10. Select one or more files you want to import and then click the Open button. The files will be imported into SonarWiz.
    
    

     

11. The imported data should be listed in the Project Explorer under the Forward Looking Sonar Files branch:
    
    

     

    And it will draw in the main display similar to sidescan files:
    
    

    If there are along-track data gaps reduce the skip frames and re-import. If the data looks too blurry at the edges, reduce the width of the sampling window.

12. Control the colors of the image by changing the Forward Looking color settings in the Color window.
    
    

    NOTE: These settings also control the color of the image in the FLS Sampling Area Chooser

13. Right-click an FLS file in the Project Explorer to see the FLS Context Menu. The FLS Context Menu lists the commands available for FLS files:
    
    

     

14. At this point FLS data are much like sidescan files. You can create image mosaics, run project reports and combine FLS data with other data types such as true sidescan, multibeam and sub-bottom data. However, you cannot currently use the waterfall displays for FLS data and you cannot yet pick contacts in FLS data. We plan to expand the functionality available for FLS data sets in the future.

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