Hydrophones give you distance as well as bearing?

[difool2]

Possible spoilers below!


File this under the "Things I never really paid attention to until now" category...

Driving a XXI in '45. Noticed that as a contact (DE) got closer the contact line seen
via the hydrophones kept getting shorter. Felt this was odd since shouldn't the line
get longer (representing signal strength) as the contact got closer? Eventually popped
the scope up for a second and lo and behold the ship icon on the nav map perfectly
matched up with the end of the black contact line. Guess this models the sound guy
estimating distance based on the sound level and the sound "cone"-tho he's probably
much too accurate. Still need to estimate target AOB on your own but given this
information that should be a piece of cake (just X the end of the line every so often
and bingo you have his course).

I did a search for this but nobody else here seems to have noticed this-either I'm the
first (unlikely), nobody's discussed it, or something.

[Rykaird]

Yes, this works. The distance might be off by a few kms or so, but the direction is dead on, especially if you zoom in all the way to make your marks.

It's a huge cheat given the accuracy, but I had an entire thread going on how to estimate target course using the hydrophone and never really got an answer on how to do it, other than this technique.

http://www.subsim.com/radioroom/show...ght=hydrophone

Most of the guides on targeting rely on visual contact, but I hunt a lot in bad weather, and I just need an approximate course from the hydrophone so I can plot an initial intercept to get into position for the visual.

[Brag]

By being careful where one marks the estimated position of the contact, one can establish a very accurate course of the target and be within 50 meters when the target show's up in low visibility.

I also use the sonar lines to track the movement of escorts when attacking a convoy in the daytime without raising my periscope after initial visual contact

[Rykaird]

Originally Posted by Brag

By being careful where one marks the estimated position of the contact, one can establish a very accurate course of the target and be within 50 meters when the target show's up in low visibility.

I also use the sonar lines to track the movement of escorts when attacking a convoy in the daytime without raising my periscope after initial visual contact

Yup, works great. But no hydrophone operator is possibly capable of such a feat - estimating the range to a contact 10kms away to a matter of 50m. So the question on the table is that if you don't use this rather forgiving technique, how would one get a rough course using just the hydrophone?

[Iron Budokan]

It's very difficult. You can take a sonar bearing, move your position and take another, and try to triangulate subsequent positions of the moving merchant. Like I said, very difficult and the "triangulation" is very coarse.

[Dantenoc]

The reason that this technique is rarely discussed is that it's useless once you turn off the "God's eye view" on the nav-map, hence eliminating the sonar lines. This means that by the time your smart enough (game wise) to figure out stuff like this you immediatly feel the need to go "hardcore" and play without the map auto-update feature, thus making this irrelevant.

Now, as to true "target motion analysis", it can be done, specially if you take advantage of the "short", "medium" and "long" descriptions that the sonar man gives you for the target's range... weather or not it's ok to do it, that's up to you, since TMA is a modern technique that wasn't really used much back in WWII.

Observe the next picture:



The "X" marks represent my boat's position at different times as I was outflanking the sound contact. For each of those there is also a "sound contact line" that I drew, namely, the four 2km long lines and the 1km long line at the end. Each of them is drawn following the contact's bearing that was given to me by the sonar guy at the moment it was made. The first four don't start at my boat's position (the X marks) because at the moment the contact was called out as being in "medium" range, hence they start 1km away from me (shor range) and end 3kms away from me (long range). The last one does start at the X mark and ends only 1km away from it because at the moment the target was called out as being in "short" range. After that, it was just a matter of drawing a big line that represented the target's track, that would cut through all the lines that I had drawn and that would make sense as a probable target's track.
To sum it up:

Short range: from 0 to 1km
Medium range: from 1km to 3kms
Long range: from 3kms to .... probably 15 kms, depending on how good your sonar man is.

Here's another example:



In both cases I was forced to use this technique because of bad weather and nill visibility, here's the result of both:





One last thing, be warned that this method needs to be changed a bit if your using GWX, since they decided to alter the definition of "short", "medium" and "long" range. Here's the updated values courtesy of Steppenwolf

Yes, GWX changed the definitions for Short, Medium or Long:

Sonar contacts in Original: Short - 1000, Medium - 3000, Long -20000
Sonar contacts in GWX: Short - 1000, Medium - 8000, Long - 16000

Cannon in Original: Short - 1000, Medium - 3000, Long - 5000
Cannon in GWX: Short - 1000, Medium - 5000, Long - 10000

AA Gun in Original: Short - 500, Medium - 1000, Long - 1500
AA Gun in GWX: Short - 1000, Medium - 3000, Long - 4000

[Rykaird]

Dantenoc - this is fantastic stuff. I feel like I've found some ancient text scrawled with deep secrets of the past.

So I completely get the idea of the 2km line, on the bearing called out by your sonar man, starting 1km away from your boat. That represents the possible locations of the enemy - he must be somewhere on that line. That alone is a big help.

Could you explain the logic behind where you drew the course line through all of these possibilities? How are you "reading" the succession of lines to get that overall estimate of his course?

[Dantenoc]

In reality, your constatly redrawing the target's track as new "sound contact" lines are drawn. The basic assumption is that the enemy is traveling in a straight line (so that means that the systems doesn't work too good on a zigzaging target, and flops miserably if the target changes course) So your always trying to figure out what straight track satisfies the condition of crossing all of the different "sound contact" lines that you drew. In the begining, there's an almost infinite amount of different posibilities, but pretty soon, as you draw more and more contact lines, it will become very evident that there is only one possible solution. Specialy when you are able to catch the change from long to medium range or from medium to short range. The "choke points" created there limit the possibilities down a lot.
You can see this in action more evidently in the second example. In it the target was traveling from the right of the image to the left, with a course of about 260 degrees (I forgot the exact heading). From the right to the left, the first five lines correspond to the target being at long range. Then theres four more lines, continuing to the left, that were made at medium range, and then there's one last one made at short range. That creates two choke points (at spots where the target closed range from one level to the next) that pretty much narrows the posibilities to almost only one solution.

Of course, it really helps if you have obtained your target from a "radio contact" (the ship icons that pop up out of nowhere on the nav-map) since that will fix one of the end points for the target's track (which is why in the first example I only required so little "sound contact" lines before I knew the target's track dead on).

[Corsair]

For those who would like to keep the map contact updates but have some uncertainty, there has been a mod released for GWX 1.02 similar to the Assisted Plotting Mod used in NYGM. You can only track one visual contact at any time on the map and the sound contacts are shown by dotted lines which don't give the precise distance away.
Check in the Mods Workshop forum.

[Brag]

There is another method, which is quite accurate: THE RUNNING FIX. You must stop.

You draw the bearing of your first sound contact and mark your position. Wait 3 or 6 minutes and advance your position at the estimated speed of the sound contact

Take another bearing and advance your old bearing to this new (fake) position. this will give you a fix on the target.

[Rykaird]

Originally Posted by Brag

There is another method, which is quite accurate: THE RUNNING FIX. You must stop.

You draw the bearing of your first sound contact and mark your position. Wait 3 or 6 minutes and advance your position at the estimated speed of the sound contact

Take another bearing and advance your old bearing to this new (fake) position. this will give you a fix on the target.

Oh, how I wish I understood this.

1. "You draw the bearing of your first sound contact and mark your position".

Got it.

2. "Wait 3 or 6 minutes and advance your position at the estimated speed of the sound contact."

So the three or six minutes - is this related to the 3 min 14 sec rule?

When I "advance my position" is this in any direction, or on the original target bearing?

Got the speed - that's from "slow, medium, fast" from the hydrophone operator and using the standard speed ranges for those terms.

3. Take another bearing and advance your old bearing to this new (fake) position. this will give you a fix on the target.

Nope. Your brilliance met a brick known as my forehead on this.

Brag/Dantenoc - I know I'm the Gilligan and you two are the Professor in this little play, and I really do appreciate your help. Don't give up!

[Iron Budokan]

Dantenoc is an absolute genius. I always learn a ton when I read his posts...

Rykaird - do not despair, i did not "get" it either.

But this page explains it for dummies like us

http://www.patentstorm.us/patents/55...scription.html

http://www.subsowespac.org/tactics/sj_radar.shtml

[Dantenoc]

Originally Posted by Brag

There is another method, which is quite accurate: THE RUNNING FIX. You must stop.

You draw the bearing of your first sound contact and mark your position. Wait 3 or 6 minutes and advance your position at the estimated speed of the sound contact

Take another bearing and advance your old bearing to this new (fake) position. this will give you a fix on the target.

Interesting :hmm: ... picture please

[joegrundman]

I'd like to point you to the following link which shows my tutorial on how passive sonar alone (using NO automatic map contact updates) can be used to estimate speed, AOB/course and range. You will still need a periscope observation befroe firing. but you can get very close and be ready to fire before a periscope sighting is made.

http://www.subsim.com/radioroom/showthread.php?t=115366