360 Sonar to supplement smaller laser scan projects

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jcoco3
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360 Sonar to supplement smaller laser scan projects

Post by jcoco3 »

Just a preview of something I have been working on. Can't go into too much detail right now, because it is still a work in progress.
Static 360 sonar scan of a portion of a swimming pool ~8' deep and 10'-15' wide:
SonarScan1.PNG
SonarScan2.PNG
SonarScan3.PNG
The big red dot is the center of the scan, and the rest of the pool should be obvious aside from a small ledge that was mostly missed from being too close to the transducer for the settings I used.

Its not much, but the idea is to supplement our laser scans above the waterline with some short range sonar scans in the muddy waters below. While we have done some larger multi-beam work on a number of projects (https://www.youtube.com/watch?v=tPpZsU7Q8Ao), we are looking for a way to fill the void in close confine spaces like pump stations, sumps, and tanks. Constructing most of this system, and working out all the mathematics has given me an entirely new appreciation for the work that goes into building a laser scanner.

I still want to get my hands on a BlueView BV5000-1350, but its not in the cards at the moment and might be more difficult to deploy by comparison.
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Re: 360 Sonar to supplement smaller laser scan projects

Post by landmeterbeuckx »

Very nice Jonathan, this would certainly benefit some projects because not that many points are needed to visualize a certain object under water or even a depth for engineering purposes.

Scanning manholes full of water for exemple so all pipes can be visible with their depths.
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Re: 360 Sonar to supplement smaller laser scan projects

Post by mike annear »

Very Nice !
I think there would be lots of uses for a decent underwater scanner.
Could you modify one of these commercially available transducers ?
https://www.youtube.com/watch?v=q-TtJcE ... e=youtu.be
Regards,
Mike.

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Re: 360 Sonar to supplement smaller laser scan projects

Post by ddustin »

As always, Jonathan Coco is pushing the boundaries..
He's a true rock star in the 3D world :ugeek:
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Re: 360 Sonar to supplement smaller laser scan projects

Post by jcoco3 »

Thanks guys:) Thanks David! The feeling is very mutual :P

Mike, That Garmin Panoptix is an imaging transducer...so short answer is no if you want a point cloud, yes if all you want is an image that can give you a horizontal range to objects. Its confusing, but you can take my word on it... I have been far down the road on 3D data from imaging and side scan transducers and I think its a dead end...for now. Even Simrad's 3D Structure scan is more or less just sidescan with some incredible visualization algorithms to automatically interpret intensity based slope from the sidescan image. Its very cool for fishing and imagery, but not a very accurate measurement tool. We own a Humminbird Solix 10 with the 1.1 megahertz side scan transducer and the 455 kilohertz 360 imaging transducer. With Chirp enabled they are really nice, and are perfect examples of the consumer grade stuff somewhat catching up to the commercial grade. Great for search and recovery.

1mhz Humminbird Side Scan of an upside down car buried in the mud (same that was highlighted in previous video link) we helped pull from a river. You can see the mud the divers stirred up around the car. Shadow of divers legs at the bottom.
Car and Divers.PNG
~10'-12' log @ 15' deep
Log.PNG
360 transducer 455khz from a stationary point(lower resolution, but longer range). Small ~50'x50'pond ~6' deep. What are the little structures in the middle creating shadows...who knows.
snp0210185157.jpg
Same 360 transducer...unusable image of a swimming pool...way too much multipath!
snp0211182226.jpg
40' long 36' diameter culvert location in a pipeline ditch that is ~8' deep.
Culvertlocation1.PNG
Same culvert observed in side scan. external corrugations showed up from internal scan due to different return on signal intensity. Centerline is boat track.
CulvertSonar1.PNG
Both produce excellent imagery, but are a far cry from the data and imagery we are exposed to in laser scanning. While they are both great at roughly "locating" objects sidescan(they are both types of sidescan) generally only produce a single depth measurement (sounding) beneath the transducer. We have used this single depth measurement on the "mega" transducer to map out some a fairly large areas in a rover or "mowing" mode with good results. Good precision as it compares to a very expensive multi-beam hydrographic setup in shallow water, but once you get beyond tens of feet the ranging will be way off due to temperature and salinity changes in the water column that must be compensated out by readings from a separate Sound Velocity Profiler. The commercial software (Hypack, SonarWiz...etc) can integrate this data, but the consumer stuff is not even in the same book much less the same page.

The following images show mostly data from a multibeam hydro system using an R2Sonic 2024 (color ramp), Single soundings from a Sonarmite coupled to a Trimble R10 gps (Red points), and then in brown points are what was captured by mowing the lawn from a kayak with the Humminbird Mega (position adjustments made in post)
image030.png
image031.png
image032.png
In brief, the Humminbird data was much better than expected and was consistent with the R2Sonic multibeam. The Sonarmite data was taken a year earlier so most of the difference is due to change in the bottom profile.

So, why bother with all these examples...to help explain that the nature (physical limitations) of sonar produce results that are a far cry from the worst results you see from anything in laser scanning.
I think there would be lots of uses for a decent underwater scanner.
My response to that statement after all that I have learned...The BV5000 is the decent sonar scanner. Yes its very expensive, difficult to deploy and operate, the range is short and the resolution is low (compared to laser scanning), reflectivity is terrible, etc...but this is likely the best we should expect from the limitations of sonar for a long time. Even with the advent of SAS (synthetic aperture sonar) I don't see this making any improvements to a static type sonar scanner. Sonar is very limited by the properties of mechanical waves as compared to the electromagnetic advantage of lasers. When you shoot a laser across the room the coherent light hits the wall and diffuses everywhere with a portion of the photons returning to the scanner, but after using sonar for a while you will start to realize it is like throwing a handful of marbles at the wall and hoping that one might bounce back and hit the transducer. Lots of tuning and tweaking to even get a return (or at least a good one), but this is common to the sonar/hydro industries most expensive equipment. And don't even get me started on beam divergence! Too late! Faro laser scanner with 0.19mrad beam [email protected] meters = 2.24" or 57mm spot size. I hope that math was correct. So lets take one of the highest commercially available sonar frequencies (2.25Mhz). Higher frequencies have less beam divergence, but it is not even close to what a laser can do. 2.25Mhz 1.4 degree beam angle is typical, so if the wave doesn't attenuate before it gets to 20' of range then the spot size would be 5.9" or 150mm! That is Nasty! Range is another weird one since you want to stay high frequency to keep the beam divergence low, but the higher frequencies attenuate sooner, so you have to go with lower frequencies for longer range resulting in a poor ability to resolve smaller targets.... :twisted: GRRR its so frustrating! You basically need to own half a dozen sonar systems of various frequencies/power output/gain to capture a fraction of what you can get with a laser scanner and then the data is still extremely noisy.

Here is my pool scan before clean-up...NOISE! and oh yeah the water's surface is like a mirror at times :?
PoolSonar_Noise_Reflection.png
I believe it is just the way sonar is right now, but its still fun and it really makes you appreciate what even the crappiest laser scanner can do.

If you want to get educated enough to start working with sonar, then read Mark Atherton's Echoes and Images. Its a $200 book, but worth every penny. If you don't want to dive into sonar, then just call Echo81 for consulting and rental. They know it all and then some..not to mention they are really fun to work with :D If you want to go down the rabbit hole of the principles of sonar tech then I recommend NPS Physics series on Sonar Transducers which covers the basics of transduction and underwater acoustics: https://www.youtube.com/watch?v=_jSyqvT ... ULfXaMkxoT It's super nerdy :ugeek:
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