Question about minimum detectable object size for Sonoptix Acho 2D sonar

Third Party Products Sonar and Acoustics
1

Hi everyone,

I’m trying to understand the detection capabilities of the Sonoptix Acho 2D sonar. Specifically, I’d like to know:

  • What is the minimum object size that this sonar can detect or identify at distances of 50 m, 100 m, and 200 m?

If anyone has experience or data on the resolution or detection limits of this model, I’d really appreciate your insights or any documentation you can share.

Thanks in advance!

2

Hi @HudsonLe,

I can’t answer this one with practical experience of the device, but from the technical specification the Sonoptix ECHO’s angular resolution at those ranges is ~2.5° (although the 0.47° beam separation means ~5 beams will be hitting an object the width of that region).

As a rough estimate, if we consider the resolution to be the minimum expected detectable object, it could be as large as \approx \text{range} \times \tan(2.5°) - e.g. ~2.2m wide @ 50m range, ~4.4m wide @ 100m range, and ~8.7m wide at 200m range. If a single beam has a very strong and directed echo response, it could conceivably detect objects a fifth of that size (or smaller, if partial response strengths are considered), but identifying the source of a single bright pixel in a reading would likely be very challenging (unless you know it is the only possible object in the water). I’m unsure how much (if any) of that extra resolution is smeared/smoothed out by the sonar’s receiving hardware and algorithm.

Note that depending on the orientation of the object relative to the sonar beam, and its density difference from the surrounding fluid, it may be possible to detect smaller objects in good conditions, but could be very challenging to detect objects at that size or larger if the conditions are poor. This list breaks down most of the variables involved.

1 Like
3

Hi @HudsonLe

That’s an easy question but a more complex answer, all of my experience with multibeams has been with other brands, but a few simple rules of thumb work

You need to be aware of some derivative of Johnson’s criteria (ie how many pixels of data it takes to detect something) eg 1 pixel is it noise or is real?

As a generalisation the more complex (in this case lumpy background the more pixels you need to identify and object from the background). Typical values are 5-7 pixels on a somewhat smooth bottom and around 10 pixels on a more complex bottom to differentiate them from the seabed and background noise

Given this unit has a Horizontal View Angle (of either 90° or 120°) the rule of thumb is for a depth with a 90° HVA the swath is twice the depth, and for 120° HVA the swath is three times the depth

The unit has 256 beams for that swath thus at 50m @ 120° horizontal view angle so about 150m swath thus giving a single pixel of 150/256=0.59m

The nominal Johnson’s criteria of say 6 pixels (some of these pixels can be along track as well as the cross track) would indicate an object around 1.5m by 1.5m

Similar concept for your other depth ranges

Scott

4

I’m planning to build a target object to test the long-range detection capability of my sonar. Do you have any recommendations for the target’s size and material? I was thinking of using a flat plastic plate, but I’m not sure if plastic would reflect the signal well enough. Metal would be better acoustically, but it’s quite heavy. What would you suggest?

5

That depends what you’re hoping to measure with your sonar.

If you’re after ideal reflections, you would need an evacuated enclosure that’s shaped as a parabolic section with the sonar at its focal point, and sized and oriented to cover the full beam width of the sonar transmissions given a particular distance.

That’s generally unrealistic though, so practical adjustments would be to:

  • If you want high reflectance:
    • Have an air-filled enclosure, rather than evacuated (it makes little difference to the acoustic reflectance, but makes manufacturing easier and leaks less likely), or use a closed-cell foam (like buoyancy foam)
      • If you do want something air-filled, and don’t intend to test at significant depths, you could cut a few sheets of acrylic (possibly with a CO₂ laser) and stick them together with acrylic glue
    • Shape it to be a retro-reflector (so it at least reflects the sound that hits it back towards the source), or a flat / slightly concave surface you can readily orient towards the sonar
    • Size it as large as you can readily obtain/manufacture the object you’re using
  • If you want realistic reflectance:
    • Size it to the smallest objects you hope to detect (in which case you can move it away until you can no longer detect it)
    • Shape it to something relatively easy to make, and test with orientations that are realistic for your expected target objects (or just over a range of orientations)
    • Use materials that you expect your target objects to be made of

Note that if you’re hoping to indicate performance for objects in general, you’ll likely need multiple test objects with different sizes, shapes, materials, and orientations.

2 Likes
6

Could you also let me know what the dB range of this 2D sonar is?

7

I’m not really sure what you’re asking (transmit intensity? receiving sensitivity?), but if a specification value you’re interested in is not available in the Technical Details section on our product page, or the provided datasheet, then you’ll need to contact Sonoptix to ask about it.