Chesapeake Times, Vol 15 | October 2023
The seabed characterization utility in SonarWiz is a valuable tool for studying underwater features. It is used to delineate seafloor topography and substrate composition from side-scan and multibeam backscatter data. The GIS layers produced by the utility are important for assessing fish habitat distribution and availability, monitoring erosion patterns and other environmental impact assessments.
One area where users have run into problems with the seabed characterization utility is in river channels and near quay walls or other restricted range environments. That is, places where the useful sonar data ends before the receiver stops recording the ping. For example, Figure 1 shows side-scan data collected near the bank of a river. On the port channel, the usable side-scan data ends at the shoreline; anything beyond the shoreline should be removed from analysis.
Figure 1: Example of a portion of sidescan data that extends beyond the riverbank. The data circled should be removed from the analysis before classification
In the current version of SonarWiz, the Seabed Characterization tool has the option to trim the far field as a percentage of sonar range (See Figure 2). This is a blunt tool in complicated environments such as a river channel or harbor and it can remove more data than desired as shown in Figure 3.
Figure 2: Seabed characterization user interface showing far trim and nadir trim controls.
Figure 3: Characterization does not extend to the banks of the channel because there was no way to define the channel margins in previous versions of SonarWiz.
In SonarWiz 7.12.00, we have enhanced the seabed characterization utility to recognize trimming and Far Field limits traced onto the waterfall of the new Side-scan digitizer window. Using trim and far field limits, the user can digitize the outer limit of sonar range, no matter how complicated, and the seabed characterization utility will ignore those areas clipped out of the data (See Figure 4).
Figure 4: Far field limits defined in the waterfall digitizer are ignored in the seabed characterization utility.
The result is that the seabed characterization utility will now be much easier to use in river channels and other environments with restricted ranges. Figure 5 shows that the riverbed characterization polygons do not extend beyond the river banks, even though the raw sonar data does.
Figure 5: Riverbed characterization polygons do not extend beyond the river banks.
The new far field and trim capabilities in the seabed characterization utility will be released with SonarWiz 7.12.00.