How do I optimise sidescan performance?

Bathyswath basically *is* a sidescan system; or, rather, it is four sidescan systems used together to measure depths as well as sidescan. One user in the USGS told us that he considers it "an excellent sidescan system that happens to give depths too".

Firstly, look at how the XTF files are being created in the Bathyswath software.
In the Processed Data Output Settings dialog, set:
- Store Good Data Only: off
- Data Buffer: Full Resolution
However, these options are only used in software versions 3.10.7 and later; for earlier versions, you will need to re-process the data with the data filters turned off when exporting to XTF (the bathy will look horrible, so don't use these files for showing depths).

When you do the survey, you need to optimise the sonar settings to get the best sidescan image. Here are some things that you can try (use a sidescan waterfall to look at the results, of course):

- Set the ping range as short as possible to cover the area you want to look at, with a little bit more for overlaps and to account for the boat not following the survey line exactly. That will give you the best along-track coverage.
- Set the receive length as high as you can without slowing down the processing: try 16384. The software might adjust the receive length down to match the ping range and the capabilities of the sonar.
- Set the transmit power to maximum, and then adjust the pulse length to get the best result; start with it short, and then increase it gradually until you don't see any more improvement in the results, then reduce it slightly again. In other words, set the pulse length as short as possible to get the sonar range that you need. That will maximise the sidescan resolution.
- Experiment with the Amplitude from Transducer Staves setting (in the Configure Sonar dialog in recent versions of Swath Processor). I usually find that setting just one of the staves (A, B, C, D) on gives the best sidescan results, and that one of them sometimes gives slightly better results than the others, according to slight differences in your system. However, sometimes using more than one stave at the same time can give better results; you will need to experiment. This selection can only be made when running in real-time: you can't change it in replay.

The other difference between Bathyswath and most sidescan-only systems is that Bathyswath is usually fixed to the vessel, but sidescan systems are used from a tow-fish, which is set to fly close to the bottom, to give the best variation in angles with the seabed as the shape of the seabed changes. If the water is fairly shallow, that shouldn't be too much of a problem. In deeper water, do what you can to get closer to the bottom, perhaps choosing a low tide or using a longer pole.

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