Chesapeake Times Vol 22 | July 2025
Getting the best resolution for your sidescan shouldn’t be a guessing game. And in version 8.4, a new tool has been added to take the guesswork out for your sidescan mosaic resolution. Why do it? I have noticed people say the project requires a 10cm resolution mosaic. And simply enter 10cm in the dialog box to create an image.
However, if one looks into the mechanics of a sidescan, (horizontal beam angle), combined with the transmit length (range) and ship speed, this value is likely not 10cm. What the user is creating is a 10cm image that looks surprisingly close to the image when processed at 20cm. The resulting geotiff file is bigger, but that doesn’t always represent a better image.
For the calculator to work, we broke down the user input to two items:
Sidescan model and the sidescan range.
Shown below is the dialog box of the Save Project as Image (mosaic of a sidescan). Next to the Specify image resolution, you’ll see a new button – Calculate.
Calculate brings up a dialog box for the user to select the sidescan and frequency (currently, we have Edgetech, Klein, CMax and GeoAcoustic). Next, select the range for the image. The calculated beam width is displayed.
The calculator will compute the beam width at the selected range.
Note: the calculation will also work if you enter in the horizontal beam width or Transducer length and frequency. If you have a sidescan model that isn’t listed, let me know and I will include it in the next update
Selecting OK automatically sets this value in the image resolution field.
The calculation features is in four places in SonarWiz; Save project as GeoImage, Export mosaic files, Individual GeoTiffs, and Save project as website
Does it work?
I captured a few images to show the values of different resolutions of the image, based upon what we’ve been told to use (“make a 10cm mosaic) and what the sidescan can actually do.
A lobster trap
On the left hand side is Image 1: 5cm. On the right hand side is the image mosaiced at 11cm ( the value determined by the calculator)
Not much of a difference.
Looking at a full image, mosaiced a rock outcropping, 75 meter range. The calculated resolution for the mosaic was 43cm mosaic (around 1Mb)
I created a mosaic with resolutions of 10cm, 43 cm and 100 cm 43 cm resolution. File size 1.5Mbyte
Looking at the same data area, mosaiced at 10cm (file size is now 20 Mbytes)
Going the other way, with a 1m mosaic, the image is noticeably different, with the rock outcropping blurred.
The calculator should be used as a guide. When creating a mosaic, you can still enter in any value needed for the mosaic. Give it a try and let me know what you think.
Happy surveying.