Sidescan Mosaic Tips – June 10, 2020
First few slides were not shown during the presentation.
We re-edited the video presentation so you can see the slides I was referring to during the opening few minutes of the presentation. I inadvertently failed to click the button to share my screen. We apologize for any inconvenience. You can view the recorded video from links on our Home, Events and Webinars Pages. Go to: Resources – Videos – SonarWiz 7 Webinars – June 10.
How does turbidity in the water column affect the data?
That is a hard question to answer. From personal experience in San Francisco Bay, CA., turbidity is not as large a problem as temperature and salinity changes in the water column. SF Bay is so turbid that you cannot see your hand below the water surface. Bathymetric LiDAR is almost useless with less than 1 m penetration, but acoustics work quite well.
What about filetype specific settings on import?
These options are mainly designed for supporting specific file formats (ie JSF, SEGY, ALL, etc.). They can affect your data but it is system specific. If you have questions about how to configure your system, please contact CTI support for guidance. We will need to know what system you are using and what file format you are recording.
Are there any options to choose raw or processed sample data when viewing or exporting a mosaic?
Exporting a mosaic is what-you-see-is-what-you-get. If you turn off all of the gain settings, you are seeing the raw data.
Do you recommend any nadir filter? and if so, what value should be used?
I recommend using the nadir filter only when you are making a very large mosaic at small scale (zoomed way out, in other words). In those cases, you want a nice uniform color across hundreds of tracklines and the nadir can really lower the quality of the image. For more detailed mosaics, the nadir filter tends to smear out the nadir more than erase it and I don’t think it improves anything. I don’t use it very often.
Do you smooth the EGN table – removing the noise in the EGN caused by individual features.
Yes, the EGN table is smoothed in recent versions of SonarWiz. This helps reduce artifacts as you suggest.This is less of a problem when more data is available to construct the tables.
On your data I could see bright spots near nadir on one line. It seems to have affected the EGN on some of the other lines. A smoothing algorithm might be useful on the EGN.
As mentioned above, the table IS smoothed in recent versions. If you look in your EGN folder you will see an AVG table and a SMO version. The SMO version is the smoothed version used by the algorithm.
Why edge detection on only one side?
SonarWiz allows the user to either run the bottom tracking algorithms on just port, just starboard, or both. For this data set, the noise in the water column is minimal so we can assume that the altitude is the same on port and starboard. For speed, David ran the bottom tracker on the port side (with the copy setting applied) and then can make small adjustments where they do not match.
How do you overlay SS or bathy data on sub bottom data?
Stay tuned for our webinar on SBP processing on June 24. You can register here if you have not already done so.
Is there a benefit to bottom tracking both port & starboard together?
Only in the case where the staves are separated by a large distance (several meters) such as a large ROV. On a conventional fish, the staves are only a fraction of a meter apart and we assume that the port and starboard bottom track is virtually the same piece of seabed.
Is it possible for us to generate the same depth-range domain display for our amplitudes?
EGN tables are stored in the EGN folder of your project. They are organized by beam angle on the x-axis and slant range on the y-axis. The file format is the same as our bathymetry grids so you can load them into Surfer to view them, or even load them into SonarWiz as a basemap (where SonarWiz treats them as if they are bathymetry).