Ping Rate Limit for Omniscan Side Scan Sonar

Third Party Products Sonar and Acoustics
1

Hi all,

We have an Omniscan 450 Side Scan Sonar, and we recently did a test comparing the effect of different ping rates on the sonar image. For a 15 m scanning range, we got the best results for our use case at 50 pings per second, but we later noticed that the BlueRobotics page for the sonar lists the maximum ping rate as 20 pps (for 30m). I figure that this rating just means that above 20 pps, your scanning range is limited below 30 m due to time constraints of the higher ping rates, but we just wanted to double check that we overdrive or damage the transducers by running 50 pps.

Thank you.

2

Hi @bmenard3 -
This may be a better question for Cerulean’s Sonar’s support team. The SonarView interface doesn’t allow setting the ping rate above 20pps, maybe for the reason you detail with time constraints. Are you collecting data with your own software?

3

Hi Tony,

Ok I can reach out to them. We use their API to control the sonar through Python Scripts, and there’s no enforced-limit on what you can set the ping rate to with it.

4

This doesn’t quite sound right

Speed of sound in water is around 1450-1500m/second

At a 30m range (60m flight of sound there and back)

ASSUMING no processing time and exactly the range (typically it is a bit over (say 35m in this example))

So about 0.04 seconds for the sound in the water

Thus around 25 pings per second

Anything above that you have multiple pings in the water column

5

As I said, we are using the 50 pps setting at a 15 m max scanning range, and our actual area of interest is closer to 8-10m.

6

Yeah, \frac{1500 m/s}{2\times 15 m} = 50 Hz , as the theoretical limit of scanning at that range.

That might be possible if the sonar communicates a stream of profiles while simultaneously transmitting and receiving, but it could also be rate limiting under the hood, or giving duplicated profiles if you ask for them too quickly. Have you tried measuring the rate you’re receiving the profiles?

Whether a specified rate of 50Hz can cause transducer damage is something you’d have to ask Cerulean. The 20Hz maximum is also specified in their technical details, but it’s not clear whether that’s transducer-related or just a typical value for customers who want a simplified interface to it.

7

@bmenard3 and I have since this discussion on our Cerulean support site. I checked the firmware code and to my surprise, there is no enforcement of the 20 pps limit! I don’t think we’ll change the spec, so if it works, then it’s a bonus! Thanks for this interesting discovery.

When using Omniscan via SonarView, SV is limiting the ping rate to 20pps. Maybe we’ll do some testing this summer and see if we want to change that.

And of course as noted above, ping rate is indeed limited by the range and speed of sound. We don’t ever purposely have more than one ping in the water at the same time within the specified range.

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