[RESOLVED] SOSUS performance

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[RESOLVED] SOSUS performance - 4/24/2021 3:19:33 PM

AndrewJ

Posts: 2318
Joined: 1/5/2014
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Hello,

I was trying out SOSUS performance using the new sonar model in B1147.21. Here are a couple of tests, one with a Victor I, the other with a Foxtrot, both reasonably noisy targets from the era when SOSUS had excellent performance. Tests were run at a combination of standard depths and speeds using the buttons in the F2 window. Sensors were in the G-I-UK gap. (Because of the shallow layer here, this actually makes 'just over the layer' slightly higher than the 'shallow' depth setting.)

Here's the results I got for a sensor in the 2km deep water east of Iceland, north of the Faroes.

A few items caught my eye.

Ranges are mostly in the area of 140 to 160 miles, which would be great for a sub or ship-mounted sonar, but seems short compared to the ocean-spanning ranges the system was reportedly capable of. (The DB gives it a range of 1000 miles.) If the sensor is placed at shallower 900m depths NNE of Iceland, where no CZs are indicated, detection ranges drop to only 50 to 60 miles.

In most cases, speed and cavitation didn't make a difference in the detection range. A Victor creeping at 5 knots was detected at the same range as a Victor cavitating at a full 22 knots.

Performance against deep targets was generally worst of all, which surprised me. I had expected that the seabed-mounted sensors would do best on deep targets, but they actually do better against targets further away on the other side of the layer. Wouldn't their best detection ranges be against targets which are already down in the deep?

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< Message edited by Dimitris -- 5/1/2021 7:46:34 AM >

Post #: 1

RE: [B1147.21] SOSUS performance - 4/24/2021 6:29:44 PM

thewood1

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Joined: 11/27/2005
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I got interested in SOSUS use a year or so ago and did a little amateur research on it. The link below stated that a 80s era Soviet nuke sub could be localized from 50 miles away. The attached paper stated that in the 80s a number of Soviet nuke boats became undetectable through SONUS due to changes in their noise profiles.

https://dosits.org/people-and-sound/national-defense/how-is-sound-used-to-find-submarines/

The attached PDF I found very helpful in understanding SOSUS better. Because of propagation issues, some of the performance of SOSUS and other deployed arrays is a little counterintuitive. Doesn't address you question directly, but I found them helpful.

Attachment (1)

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(in reply to AndrewJ)

Post #: 2

RE: [B1147.21] SOSUS performance - 4/27/2021 3:30:37 PM

p1t1o

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Joined: 4/6/2015
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quote:

ORIGINAL: AndrewJ

Performance against deep targets was generally worst of all, which surprised me. I had expected that the seabed-mounted sensors would do best on deep targets, but they actually do better against targets further away on the other side of the layer. Wouldn't their best detection ranges be against targets which are already down in the deep?

Think of a radar on the ground - does it perform better against targets at 200ft or 20,000ft?

Radio and sound waves do not exactly behave the same way, but the effects are analogous - ground reflection clutter, line of sight, various layers in the propagating medium that affect transmission positively or negatively etc.

< Message edited by p1t1o -- 4/27/2021 3:34:09 PM >

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Post #: 3

RE: [B1147.21] SOSUS performance - 4/28/2021 2:14:07 PM

WSBot

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Joined: 1/17/2021
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0014528

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Post #: 4

RE: [B1147.21] SOSUS performance - 4/29/2021 12:00:12 AM

AndrewJ

Posts: 2318
Joined: 1/5/2014
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Well, let's consider the geometry of the example I tried.

We have a situation where a seafloor-based sensor can hear a target much further away (1.7 times), when it is further up, and on the far side of the discontinuities of the layer.

(Relative horizontal positions to scale, relative vertical positions of subs and layer to different scale, seafloor not to scale.)

Why? The SOSUS array is down below the turmoil of the surface waters and the layer, taking advantage of the more homogenous waters below. What obstacles are there from the sensor to the deep sub, that are not also present to the shallow sub?

Ground clutter / reverberation and LOS issues? I think it's probably not an issue in this case. Because the ranges are so great, compared to the vertical distances, the angle of elevation from the sensor to the near sub is just 0.63�, and only 0.44� to the far sub. The difference is only 0.19�. (Neglecting the curvature of the earth, sorry.) For practical purposes, they're the same. At these ranges the sound from both targets is essentially travelling horizontally with respect to the sensor. Any bottom terrain issues which affect one should also affect the other.

Once the sound gets deep it can go a long way. But it has to get there first, and that is presumably more difficult for the sound from the shallow sub than the sound from the deep sub.

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RE: [B1147.21] SOSUS performance - 4/29/2021 1:13:38 PM

Dimitris

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Joined: 7/31/2005
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Can you please check with B1147.22 .

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RE: [Logged] SOSUS performance - 4/29/2021 3:00:53 PM

c3k

Posts: 369
Joined: 4/25/2017
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quote:

ORIGINAL: AndrewJ

Hello,

I was trying out SOSUS performance using the new sonar model in B1147.21. Here are a couple of tests, one with a Victor I, the other with a Foxtrot, both reasonably noisy targets from the era when SOSUS had excellent performance. Tests were run at a combination of standard depths and speeds using the buttons in the F2 window. Sensors were in the G-I-UK gap. (Because of the shallow layer here, this actually makes 'just over the layer' slightly higher than the 'shallow' depth setting.)

Here's the results I got for a sensor in the 2km deep water east of Iceland, north of the Faroes.

A few items caught my eye.

Ranges are mostly in the area of 140 to 160 miles, which would be great for a sub or ship-mounted sonar, but seems short compared to the ocean-spanning ranges the system was reportedly capable of. (The DB gives it a range of 1000 miles.) If the sensor is placed at shallower 900m depths NNE of Iceland, where no CZs are indicated, detection ranges drop to only 50 to 60 miles.

In most cases, speed and cavitation didn't make a difference in the detection range. A Victor creeping at 5 knots was detected at the same range as a Victor cavitating at a full 22 knots.

Performance against deep targets was generally worst of all, which surprised me. I had expected that the seabed-mounted sensors would do best on deep targets, but they actually do better against targets further away on the other side of the layer. Wouldn't their best detection ranges be against targets which are already down in the deep?

Outstanding.

Thanks for looking at this and posting such a great consolidated visual of the data you collected.

(in reply to AndrewJ)

Post #: 7

RE: [Logged] SOSUS performance - 4/30/2021 11:27:56 PM

AndrewJ

Posts: 2318
Joined: 1/5/2014
Status: offline

Here's what I found in B1147.22.

SOSUS detection ranges have increased significantly.

Here is an example of detection ranges against a Victor I at creep speed at various depths. In the previous model, detection ranges had a maximum of just under 170 nm, and now they are up to as much as 370 nm.

Worst detection range is above the layer, and it gets marginally better (only a few miles) in the layer

The longest detection ranges are in a 70 m thick zone under the layer.

Detection ranges drop again as the sub gets deeper, and remain a few miles better than against targets in or above the layer.

The detections under the layer being better than detections in and above the layer makes intuitive sense. The drop in performance as the sub continues to get deeper still has me a bit puzzled. Is this how the deep sound channel is being modeled, in that you can actually get below it into an area of less efficient transmission?

(I think the main lesson here is don't be a Soviet submariner in the late 60s / early 70s!