Effects of Depth on Sonar

[MBot]

Hello everyone
I haven't been here for years, perhaps one or two remember me from past Sub Command (and SCX) times. Yesterday I played Dangerous Waters again and it was great fun!

Now I wondered about sonar performance and depth, because frankly I can't remember how that worked in-game. How does your own depth and the depth of your targets affects detectabilities (both ways). Does depth actualy matters at all? Of course disregarding the obvious layer effects and surface noise.

What are the best depths to detect ships and subs at various depths (for each SSP)? What are the best depths to stay undedected?
And while surface noise will degrade own sonar performance at shallow depth, will it actualy cover my ownship noise?

In a enviornment without layer, will it actualy matter wether I drive at 400 or 1200ft (in game)?

[Dr.Sid]

My tests showed that besides the layer effects and surface noise, depth has no effect. It's 2D problem. Depth is only used to detect on what side of the layer you are.

All the results are here:
http://www.subsim.com/radioroom/showthread.php?t=117814

[MBot]

Thanks, fascinating read.

[Molon Labe]

http://www.subsim.com/radioroom/showthread.php?t=124973

Sonoboy's tests showed a link between detecting platform depth and detection range, when the contact was at the surface and the detecting platform was below the layer in a surface duct SSP. My interpretation of his data is that DW increases modeled transmission loss at higher velocity points on the SSP. I doubt this is only applicable to cross-layer detections.

I have accidentally attributed this data to Dr. Sid in the past, so I apologize to Sonoboy.

EDIT: I can't say I fully understand Dr. Sid's data on the shadow zone (the half on the SNR vs range is simple enough though) but my best guess is that it shows a "longer" shadow zone at depths closer to the layer--that the shadow zone extends closer to the detecting platfrom at shallower depths. That is completely consistent with Sonoboy's data showing a significant correlation between depth and detection range.

[Dr.Sid]

Yes .. the shape of the front 'edge' of the shadow zone can be seen on my data too, but not clearly. Sonobuoy made it clear.
But this only extends the layer mechanism a bit. And it is shadow zone SHAPE alone. It does not affect transmittion loss. It stays constant, until you enter shadow zone, then it becomes zero.
Also the front slope of the shado zone is quite steep, I doubt it could be used much.

[Molon Labe]

Originally Posted by Dr.Sid

Yes .. the shape of the front 'edge' of the shadow zone can be seen on my data too, but not clearly. Sonobuoy made it clear.
But this only extends the layer mechanism a bit. And it is shadow zone SHAPE alone. It does not affect transmittion loss. It stays constant, until you enter shadow zone, then it becomes zero.
Also the front slope of the shado zone is quite steep, I doubt it could be used much.

I've been applying it to active sonar evasion over the last few months, and found that it can make the difference between getting in range for a USET shot or having a ton of ASROCs shot at you.

[Dr.Sid]

Hm .. I see .. yes, it's better to go to depth just below the layer, than deeper.

[MBot]

I have been using the 'just bellow the layer' approach a couple of times and it works quite well.

What I still wonder is how exactly does shallow depth affect sonar dedection. I know that the increased ambiet noise close to the surface decreases my own sonar performance. But does it also help to mask my signature? Will I be less detectable by lets say a surface ship when operating at PD compared to 250ft?

On a similar note I wonder how the acoustic condition areas on the nav map work exactly. As we know, the different shades of blue on the nav map do not idicate depth but rather acoustic conditions. The question is, where in calculation of the game do they take effect? Will they effect the sensor only (by reducing effectivity) or also the source (by masking emissions)? What about the in between? Let's say both sensor and source are in good acoustic conditions but in between them is a region of bad ones. Is the travel of sound trough that region of bad acoustic conditions taken into account by the game?


My last question is unrelated but I don't want to open a new topic just for that. When using the active sonar of the FFG I noticed that some seconds after the ping I saw a second "wave" traveling up the display. I guess this is some sort of bottom bounce effect, where some sound waves have taken a longer route that took longer. What effect was it exactly that I have been observing here? I can't remember the exact SSP, it was in about 250ft deep water and general bad acoustic conditions.

[Dr.Sid]

Now that is old HOAX ! Color on the map is combination of depth and 3d shading. It has nothing to do with sound propagation. I really wonder where this idea came from.

As for the second wave, it should not work like this, since the reciever can't tell bottom bounce from direct reflection. Bottom bounces should just create false contact little far away from the real contacts.
Anyway I have never seen anything like 'second way'

[MBot]

Now that thing about the map colour is funny, I think that has been around since 688(I) H/K.

On the active sonar thing, I actualy saw a second "false" contact a bit further out. And I also saw a second run of screen refreshing going over the screen when the primary ping reached the far end of the screen.

[Dr.Sid]

Try to post screen, or save.

And btw. what platform you were in ? Since you play since 688 .. are you aware that as the ping reaches far end usually next ping is sent ? :-D

[MBot]

It was on the FFG, single ping mode. I still remember the mission, will try to recreate it later and make a savegame.

[MBot]

It's funny, but I have not been able to recreate the second ping thing. Played the mission again and drove to the aproximatly same spot on the map, but this time all seemed normal.



But while playing mission 2 of the perisher campaign I noticed something strange that seemed to be in contrast to the previous testings of the shadow zone. I created a test mission to check it out further:

Latest LWAMI
Ownship is 688(I) at 5 kts and various depth
Oponent is 688(I) at 5 kts and 350ft
SSP is CZ with layer at 390ft, seastate 3, rock bottom and 10'000ft water depth.
Goal was to check out the boundarys of the shadow zone depending on depth. What I did is observe the broadband sphere sonar and note the range at wich I would pick up the other sub. Since the shadow is about completely block sound, SNR and sensor sensitivity should not play a role.

Here are the results:



-What is strange are the variations between 400 and 550ft.
-And what is realy strange is the immense drop in detection distance when ownship is bellow 800ft.


I did some more tests with the speed of the enemy sub at 32 knots to verify that the shadow zone is realy about cutting all sound and not dependent of SNR. Since changes to the mission meant I could not play from the same savegame as with the first test, the layer depth varied a bit and therefore the results were not exactly the same. But they seemed to generaly support the first results. At great depth I would not dedect the other sub even at 32kts until range was down to about 1.2 NM, then he would pop up on broadband in all his brightness.


This is all rather confusing and seems to contradict many tests that were done here previously. Anyone can make sense out of that?

[Molon Labe]

Easy. Sonoboy's tests were in a surface duct SSP. Yours are in a CZ SSP. Apples and oranges.

[MBot]

But does Surface Duct or CZ realy matters in ranges bellow 8 NM? What is the difference in behaviour?

Regardles of the previous tests, what is the explanation of what happened here?