Tatics advice please: How do I beat active sonar?

[Deathblow]

So I'm playing a shallow water recon op, Bill Nichols' Belling the Cat, where I monitoring the naval traffic out of Severomorsk. Problem is, a Russian FFL with active sonar blasting is heading straight my way at 35km and closing. Don't want to run, I really need to monitor the SSBN traffic, but I don't want to be detected.

So my question is:
How do I evade its Active sonar? Is my only option to turn the other way and run?
What kindof range does Active sonar have? Will it diffinately have me at 30km? 40km? 60km?
Does the direction of the emitting ship matter? What if I move to 90 degrees from its bow? Will that lessen its chance to acquire?

I've played this mission twice and been blown out of the waters both times (Darn Russians firing on a sub in internation waters!). I can't just blow the ship outta the water, am I just outta luck? Advice from experienced sub drivers greatly appreciated.

db

[Molon Labe]

In DW 1.01, ships blasting away with active sonar will generally detect any ship within the sensor's hard-coded maximum range. I'm not positive what that hard-coded range is, but it's going to be about 10-12 miles. Put a range circle around the target and stay out of that area!

LuftWulf and Amizaur's mod has removed the hard-coded range limits so that detection range is determined more by acoustic factors. It's possible that with this mod you will be able to get much closer, although how much closer will be different in different games, depending on the SSP, bottom, sea state, detecting ship speed...perhaps even your speed (for active detection this would be a bug, but it may be the case). Aspect angle is extremely important as well...facing sideways to the emitting sonar will give a larger return, which under LW/A's mod will be detctable at longer range than the smaller return generated by facing toward or away from the emitting sonar.

[Kapitan]

stay slow and stay out of its cone ie get behind the git

[Deathblow]

Thanks for the advice.

When the water conditions are bottom limited (increasing sound speed with increasing depth) then its best to stay at the bottom right? Because the active sonar pings are going to curve upwards? as well as the returns? If my understanding of rudimentary sonar is right, that will make it harder for active sonars to detect me at the bottom, while making it easier for passive sonars to detect me right?

One more random question, related to sonar (but not active sonar): Will assigning a tracker to a signal mean that the Autocrew will update its bearing and location more frequently, rather than just detecting it and not updating the plot. Whenver I have 6 contacts and 4 trackers I'm unsure what to do.

Thanks

[SeaQueen]

Originally Posted by Molon Labe

perhaps even your speed (for active detection this would be a bug, but it may be the case).

Nope. Doppler shift is another way a target can be distinguished from background.

[Molon Labe]

Originally Posted by Deathblow

Thanks for the advice.

When the water conditions are bottom limited (increasing sound speed with increasing depth) then its best to stay at the bottom right? Because the active sonar pings are going to curve upwards? as well as the returns? If my understanding of rudimentary sonar is right, that will make it harder for active sonars to detect me at the bottom, while making it easier for passive sonars to detect me right?

One more random question, related to sonar (but not active sonar): Will assigning a tracker to a signal mean that the Autocrew will update its bearing and location more frequently, rather than just detecting it and not updating the plot. Whenver I have 6 contacts and 4 trackers I'm unsure what to do.

Thanks

In re avoiding detection:
That depends on the gradient; with bottom limited you can have a positive or negative gradient. To hide, you'd want to be near the higher sound speed.

In re trackers:
Unless you're driving a Kilo, when you mark a target a tracker is automatically assigned. If you assign more a fifth tracker on the same array, the oldest one will be removed. Trackers will send a new bearing line to TMA on the assinged contact every 2 minutes; if a tracker is not assigned there will not be any new lines sent to TMA (although, sometimes auto TMA updates without any new information, allowing you to track air targets while submerged or to track subs behind seamounts....this is realisticly impossible but that's DW's aTMA for you).

If you have more than 4 targets, try to get the louder contacts on the spherical/cylindrial array or the hull/conformal array. That way you're working with 12 trackers instead of just 4.

[Molon Labe]

Originally Posted by SeaQueen

Nope. Dopler shift is another way a target can be distinguished from background.

Do you mean that the doppler return is being proportionately modeled in the return strength? If I understood Amizaur correctly, part of the passive detection logic was carried over to active as well....although if you're right and it is modeled that way, that's very cool!

[SeaQueen]

Originally Posted by Deathblow

When the water conditions are bottom limited (increasing sound speed with increasing depth) then its best to stay at the bottom right? Because the active sonar pings are going to curve upwards? as well as the returns? If my understanding of rudimentary sonar is right, that will make it harder for active sonars to detect me at the bottom, while making it easier for passive sonars to detect me right?

Short answer: It depends.

You also have it backwards. In a bottom-limited environment, the temperature of the water cools as you travel deeper, causing the sound speed to drop with depth. It's typical of shallow water. That means the sound energy travels DOWNWARD until it hits the bottom. Whether the sound continues to travel depends on whether the bottom tends to absorb sound or reflect it. If you get a bottom bounce, then the reflected sound and direct path sound create an interference pattern that can result in a "poor man's convergence zone." If you don't get a bottom bounce, then the direct path sound is mostly absorbed into the bottom and detection ranges are extremely limited.

What you need to do to minimize the probabilty of you being counterdetected as you approach a bad guy depends on whether there is a bottom bounce or not. If there's a bottom bounce, I'd stay deep. If there's no bottom bounce, then it probably doesn't matter much where you are. His first detection will most likely be your periscope through binoculars.

Increasing sound speed with depth is typically a surface duct environment. That means that sound emitted downward is refracted back upward where, depending on the sea state, it can bounce back downward and maybe back up again. Depending on how good the duct is, the transmission loss is relatively flat and looks like cylindrical spreading.

To avoid detection here is actually relatively difficult because of the duct. Go deep, stay slow to minimize Doppler and keep your bow on the emitter. If you're not within the limiting lines of approach of the target, I wouldn't approach him. Snap some photos as he goes by and send them back to the fleet.

It's also possible that in certain shallow water surface ducts, the sound speed increases with depth, but not enough to really make me care about it. That's really a kind of "littoral mush" where sound energy stays going in almost a straight line so basically, if it's not direct path, you'll never pick it up. You get direct path just with cylindrical spreading. That's only a little better than bottom limited with no bottom bounce.

[Deathblow]

Thanks,

Advice well appreciated regarding the sonar and the trackers. Think I'll set up some dummies scenarios with the mission editor to test out the variables.

[Amizaur]

In active sonar detection the target speed-added noise is combined with target active SL, so faster you are going, larger active target you are.
This is most probably a bug. We can't do anything with this, even disable this effect, but with some good will we could imagine that it's doppler effect simulated so fast targets are more easily detected because of doppler shift...
Of course this matters only in mod, in stock game everything is detected on max regardles of speed, as was mentioned...
Also in the mod your aspect have HUGE influence on active sonar detection range, even greater than speed. So if you have to come closer to active pinging ship, come very slow, showing minimal aspect (exactly front or rear), preferably under the layer (it has some effect now). Then you can hope getting from 80% to even within 10% of enemy max sonar range. But it's not very safe because you never know what this range will be.... better to avoid them completly or get from directly behind (60 deg blind zone).

Question - what SHOULD be blind zone of surface ship's active sonar ? Should it be only 60deg like in case of FFG and all in game ships currently (300deg coverage) ?
Or maybe active should work only in 180, 200 or 240 deg front cone ?

[SeaQueen]

Originally Posted by Amizaur

Question - what SHOULD be blind zone of surface ship's active sonar ? Should it be only 60deg like in case of FFG and all in game ships currently (300deg coverage) ?
Or maybe active should work only in 180, 200 or 240 deg front cone ?

It would depend on the beam pattern.

In real world sonars, there exist multiple modes, each with different beam patterns. They allow one to adjust the sonar to make the most of the environment. One mode might be CZ mode, with a beam pattern to take advantage of a convergence zone. Another might be BB mode, for bottom bounce, intended to take advantage of a bottom bounce. Another would be surface duct mode, optimized for that. Each would have a different "blind spot" on account of the different beam pattern. Maybe in environment A it's better to focus the beam down more with an increase in array gain toward the center of the beam lobe to compensate for greater transmission loss, while in environment B you don't need to do that, so you accept less gain, but scan a wider angle.

DW has a much simplified model of this with it's omni, single beam, and omni rotational modes. In real sonars, there'd be other stuff you could do too. Unfortunately, the only one for which it adjusts the "blind spot" is single beam mode.

[PeriscopeDepth]

When using the FFG active sonar I've defintely had blind spots occuring at various ranges, bearing seems to have no effect though. And if you wait a few seconds later and ping again the blind spot will go away, or perhaps be in a different place. So what is this?

[SeaQueen]

Originally Posted by PeriscopeDepth

When using the FFG active sonar I've defintely had blind spots occuring at various ranges, bearing seems to have no effect though. And if you wait a few seconds later and ping again the blind spot will go away, or perhaps be in a different place. So what is this?

That's something different. Noise levels, reverberation, target strength, etc. need not be constant over time. There is a certain degree of randomness in them, so on one ping you might get signal excess and the next ping get nothing. As you get closer, you should get more signal excess, so the other factors which compete to keep your signal submerged in the noise become less important. There's probably a better way to say that, but it's early still. :-)