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TOPIC: Data collection recommendations

Data collection recommendations 1 week 1 day ago #11613

  • TNPower
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Hello All

I'm starting a research project which aims to map the fish habitat along an estuary. The reach to be mapped is 11 km in length and stream width varies between 100-150 m. Depth will range from 2-10 m.

I'm new to producing maps from sidescan sonar data and I'm looking for recommendations on the best settings to capture the log files. The unit I will be using is a Humminbird Helix 10 G3. From the other topics in the forum this is what I've gathered:

  • Log all sonar channels - I think this is default on the unit?
  • Set ping rate to highest possible - to maximise resolution
  • Run at 3-5 km/h - to maximise resolution

I figure if I set the side imaging extent to 30 m I'll be able to capture the entire bottom in 3 passes. I won't know what the water clarity is like until I get to the site, but this time of year visibility should be 2-3 m.

Questions:

  • What size memory card(s) is required?
  • Should each pass be recorded as a separate log?
  • Should the side imaging extent be reduced if visibility is low?
  • Will more passes be required in deeper sections?

The site is over 1000 km away and we're only going there once, so I desperately don't want to get the data capture wrong.

The field trip is not for a couple of weeks so I'll have a bit of time to do some trial runs in the local estuary.

Any advice that will expedite my learning will be greatly appreciated.

Thanks,

Trent.
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Data collection recommendations 1 week 12 hours ago #11616

  • Matt
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Your approach will to some extent depend on what the target of your research is, but I will assume that you are hoping the create the highest resolution sidescan images possible.

One important thing to consider is the ping rate, which is the number of pings that the unit will emit per second. The higher the ping rate, the higher resolution you will achieve along the direction of boat travel, but the maximum ping rate is limited by the range of the ping, since the unit has to listen for the return of each ping before emitting a new one. Speed also has a big effect on resolution in the direction of boat travel - e.g. your 5km/hr is around 1.4 m/s, so with, say, 10 pings per second you will have a maximum resolution of 10cm along the direction of the swath. You could lower your speed further, so long as you can maintain a steady course.
The upshot here is that if you limit your range a bit further (eg 20m) and drive even more slowly, you should be able to achieve better results, but at the cost of longer survey time. Finding a sweet-spot for recording quality/time spent is probably something best worked out on the water.

In answer to your questions:

1. Log size will depend to some extent on your speed and ping rate, but you can count on somewhere between 1-200MB per km as rough idea. SD cards are cheap, so take plenty and back them up after each session.

2. I have a strong preference for a larger number of smaller files. They are easier to handle and process within RM, and limit the risk of losing too much data should something bad happen to one of the files, or whilst logging a file. I'd log a kilometre or two per file, and try to keep them in the low 100's of MB each. Try to keep your passes as straight as possible, and as parallel as possible to your other swaths, with a reasonable amount of overlap.

3. Visibility of the water itself shouldn't really affect the sidescan image, unless there is a lot of actual debris suspended in the water.

4. If you've got a fixed range set on the unit, you might - I'm not sure. HB tends to increase automatic sidescan range in deeper water. You'll need to check this on the water. If the depths are within your stated 2-10m range then I don't think you'll have much to worry about.
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Data collection recommendations 5 days 3 hours ago #11622

  • TNPower
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Thanks for the reply Matt.

Resolution is important, we're aiming to classify the different fish habitats so we can do some quantitative stats. Hopefully I can sort out any issues during the trial run this week.
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