Determining Contact Depth (more RL than DW)

[Molon Labe]

Question for the sonar experts and bubbleheads out there. Suppose there is a new class of adversary boats going into sea trials, and we want to know everything there is to know about them--including what depth they test dive to. Is there a way that the boat's depth can be calculated on sonar? Or through any other means? Is there a range limit?

I did find this thread on the topic, but that's more about gameplay, I'm going for mission design criteria. Right now I'm just going with having detection held when the target levels off and assuming that the recordings can be analyzed on land to get an answer. (I'm considering adding a range limit, but the counterdetection threshold might be prohibative and baffles aren't a viable option....)

"I could tell you, but then I'd have to kill you," is an acceptable answer.

[Castout]

Perhaps there's a reason bow sonar is a spherical shaped sensor instead of stamped on like the hull sonar. Or maybe it is spherical because it is also where the active sonar is.

The truth is I don't know

But some warships had spherical air radar too and they were meant to be able to detect and track air threats in 3 dimensional space. I think so.

[TLAM Strike]

The sonar sphere is round for a reason. It has hydrophones that point both upwards and downwards, by seeing what hydrophones have the contact they can determine if its above or below.

No idea the range limit, but closer is better. I'm guessing half its maximum effective range.

@Castout: those are not spherical radars they are just a bubble around a conventional radar dish.

[Molon Labe]

Originally Posted by TLAM Strike

The sonar sphere is round for a reason. It has hydrophones that point both upwards and downwards, by seeing what hydrophones have the contact they can determine if its above or below.

The contact, or the sound? Because unless you have no gradient, the sound isn't going to come from the same vertical bearing as the contact.

[Castout]

Originally Posted by TLAM Strike

@Castout: those are not spherical radars they are just a bubble around a conventional radar dish.

Ah really thanks for the correction

Originally Posted by Molon Labe

The contact, or the sound? Because unless you have no gradient, the sound isn't going to come from the same vertical bearing as the contact.

Perhaps that's why TLAM strike suggested that the closer the distance the more accurate the direction will be(bearing and elevation)
Also bear in mind that bow sonar could and would only detect a low frequency submarine at relatively short distance already, unlike the towed array for example. Perhaps there's a big reason why they would want a less sensitive ASW sensor on their bow instead of a sensitive ASW sensor since the first would enable them directional detection despite the shorter ASW detection distances while the later would not. Or the less sensitive bow sonar is simply because the bow sonar must handle more flow noise since it's going against the sea flow directly when the sub's moving forward. But either way I think it's safe to assume that directional detection of enemy submarine could be handled by the bow sonar sphere though in relatively short distances. Enemy submarine after all is just a facet of the threats faced by submarines whose primary preys are the surface ships afterall.

If this is true this would mean that sub trailing another sub must trail them relatively close in order to ascertain their prey cruising depth and any depth change with the bow sphere sonar. I could imagine the difficulty if the trailed sub has a towed sonar thus the only way to avoid detection when trailing sub probably is by quietening the sub so much that the enemy towed array is rendered incapable of detecting the trailing sub. A major engineering feat if true and able.

Anyway there already similar threads made on this very topic years ago. Then the submarine gurus were still well active in this forum. They made fascinating read.

[Molon Labe]

Originally Posted by Castout

But either way I think it's safe to assume that directional detection of enemy submarine could be handled by the bow sonar sphere though in relatively short distances. Enemy submarine after all is just a facet of the threats faced by submarines whose primary preys are the surface ships afterall.

It might not be unreasonable to set it up to require tracking it on the bow array at the time of the test. Of course, there is no doctrine language for "Detection Held Now" with a sensor-specific argument. But I can do some range testing and that might be good enough.

Anyway there already similar threads made on this very topic years ago. Then the submarine gurus were still well active in this forum. They made fascinating read.

My search-fu wasn't good enough to find anything but the 688I thread...

[Dr.Sid]

I know vertical angle IS roughly displayed on passive sonar. There are some leaked sonar screen photos on internet, and there are 4 passive sonar waterfalls, each for different vertical angle range. It covered +5 to -30 degrees IIRC. My sonar expert called it Depression/Elevation display, with little more details (those experts .. never want to say things ), but it can help identification of targets (rather then detecting depth).
As for active, I'm clueless, except that as was told, it is really problematic for large distance to determine depth of contact even if you knew the angle.
Still there are many reasons for changing vertical angle of the active beam .. you want to send thin focused beam .. and then you have to correct for ship attitude at least. You also may want to shoot down a bit to avoid surface duct as much as possible .. or to try bottom bounce. Generally every contact will have different vertical angle for best return, depending on situation.
This should be true for passive contacts too.

[Castout]

Originally Posted by Molon Labe

My search-fu wasn't good enough to find anything but the 688I thread...

It was back in the day of Sub Command then

I'm too lazy to look LOL

and someone made similar thread too in the days DW still being hot

[TLAM Strike]

Originally Posted by Dr.Sid

I know vertical angle IS roughly displayed on passive sonar. There are some leaked sonar screen photos on internet, and there are 4 passive sonar waterfalls, each for different vertical angle range. It covered +5 to -30 degrees IIRC. My sonar expert called it Depression/Elevation display, with little more details (those experts .. never want to say things ), but it can help identification of targets (rather then detecting depth).

I think the older BQQ5 system had a manual gauge to show the elevation of the target.

[Castout]

Originally Posted by Dr.Sid

I know vertical angle IS roughly displayed on passive sonar

All sonar or just the bow one?

You could tell me then kill me

[TLAM Strike]

Originally Posted by Castout

All sonar or just the bow one?

You could tell me then kill me

I little birdie once told me that Towed Arrays give four ambig bearings. P/S + V/D.

[Castout]

Originally Posted by TLAM Strike

I little birdie once told me that Towed Arrays give four ambig bearings. P/S + V/D.

Ok kill TLAM instead

[Molon Labe]

I suppose if you can get an elevation on an incoming signal, and you have super-accurate range data AND know the SSP as well as your significant other's erogenous zones, a depth could be calculated.

[Molon Labe]

Originally Posted by TLAM Strike

I little birdie once told me that Towed Arrays give four ambig bearings. P/S + V/D.

If that's true, then the way I thought TA's got bearing (from timing the difference between when the first part of the array receives a signal to the last end) must be wrong.

[Dr.Sid]

Towed array can't give elevation. It will say angle between array axis and target. That angle forms cone around the array. So it's not even 4 false bearings .. it's infinite number of false bearings.