SCXIIC:solving out the bearing ambiguity in towed array narrowband

Stanny · 02-16-08, 10:04 AM

Thanks for advice,sonar732.My typical loadout for Seawolf is that one with emphasis on MK-48 ADCAP torpedoes (all tubes are pre-loaded with them).However,this time I have had to unload the tube during mission and reload it with only UUV.TASMs and TLAMs as well as all other gear are in stores.

I never use TASMs against surface ships,actually,as every Tomahawk is usually met with heavy barrage of anti-aircraft fire.So,MK-48 ADCAP is my weapon of choice for antisubmarine or antiship missions.

sonar732 · 02-16-08, 10:48 AM

Quote:

Originally Posted by Stanny

Thanks for advice,sonar732.My typical loadout for Seawolf is that one with emphasis on MK-48 ADCAP torpedoes (all tubes are pre-loaded with them).However,this time I have had to unload the tube during mission and reload it with only UUV.TASMs and TLAMs as well as all other gear are in stores.

I never use TASMs against surface ships,actually,as every Tomahawk is usually met with heavy barrage of anti-aircraft fire.So,MK-48 ADCAP is my weapon of choice for antisubmarine or antiship missions.

You don't have to wait until you start the mission to change your tube layout. When you see the 3 torpedo's, x, and arrow before the mission start, click on the torpedo's and change your 7 & 8 tubes to UUV.

Stanny · 02-16-08, 10:57 AM

Quote:

Originally Posted by sonar732

You don't have to wait until you start the mission to change your tube layout. When you see the 3 torpedo's, x, and arrow before the mission start, click on the torpedo's and change your 7 & 8 tubes to UUV.

Yes,I know that.I am always a bit greedy to those MK-48s,trying to take them as much as possible along.

Pisces · 02-16-08, 05:28 PM

To answer the initial question on solving the bearing ambiguity: 'Wag your tail'

Sorry guys, a layer is not going to differentiate between two bearings. If you change depth the sound on both directions are going to disappear simultaneously. Because it is the same sound. It's just that the TA sensor can't tell the difference between left and right. I know, it sounds stupid with all that modern technology. But it is just the physics/math of it. And a uuv solution is way to expensive resource wise.

Turn to a different course (a couple of tens of degrees to show it good) and see the mirror 'not real' contact shift in bearing twice as much as the course change (eventually). Since the angle between your tail (TA) and the true contact changes, the angle to the mirror contact must match (on the other side) after the turn. Which causes the sound to appear from a different direction twice as far.

This link shows a picture why it can't tell left from right (about 80% of the page down):

http://www.fas.org/man/dod-101/navy/...ys/asw_sys.htm

sonar732 · 02-16-08, 10:08 PM

Quote:

Originally Posted by Pisces

To answer the initial question on solving the bearing ambiguity: 'Wag your tail'

Sorry guys, a layer is not going to differentiate between two bearings. If you change depth the sound on both directions are going to disappear simultaneously. Because it is the same sound. It's just that the TA sensor can't tell the difference between left and right. I know, it sounds stupid with all that modern technology. But it is just the physics/math of it. And a uuv solution is way to expensive resource wise.

Stanny actually mentions a course change.

My layer change tactic is to hide you launching a UUV from the contact. If he would've launched the UUV in the same layer, he probably would've tipped off the AI depending on the SSP. Stanny's history in sonar questions show that he's learning on the fly and doing a good job at it.

Pisces · 02-17-08, 06:11 AM

Allright, I missed that part about his course change then. Also I'm sorry if I sounded a little tough. Bad excuse, but it was getting late. Anyway, I think he is getting confused on what the narrow band suite is showing him.

The top window shows frequency(horizontal) versus time(vertical) of only one bearing out of 360 degrees. This bearing is selected by clicking and moving the cursor in the bottom window. That one shows signal level(vertical) versus bearing(horizontal). As long as the cursor in the bottom windows stay put the top window can't show sound from other directions. The middle window is only showing what the sound ID database thinks it hears. You can ignore that for now if you only have 1 or 2 lines. On the bottom window only loud contact stand out as a peak. You won't notice silent subs in that wobbly noisy graph. But they are there. You do scan a bearing in it, but only look for evidence of a contact by looking for lines in the frequency window. Those are not going to wave left or right, just fade-in or -out. When he found a 50hz signal on one bearing there should also be a 50 hz sound on a bearing that is "2xCourse - target bearing" (maybe need to correct by subtracting/adding 360 deg) So if he's on course 38 and detects a contact on true bearing 178, the other signal is on 2x38-178=76-178=-102=258. Both bearings are equal distances to your course or TA direction. If you confirm there is a contact on 258 you write both down, or assign a tracker to each. I preffer the former, as there are only so many trackers you can assign (4), and paper is cheap. But assigning a tracker is best if you are learning, because you can see it happen on the map. Make sure you turn OFF auto-TMA before doing this, or that crew member will take away the fun.

Now, do the turn (let's say 30 degrees, and atleast some 4 minutes after assigning the trackers because they need to average out or something) and wait until the TA is straigtened and has been towed past the turn end point. (this can take a long while if you are slow, do not extend the TA fully, a 3rd is enough most of the time) Then try those bearings again. Which one stayed put? (within a few degrees, as it may move on it's own if the turn and straightening took a long while) That is the true contact. Which one isn't there any more, that one is likely the mirror/fake contact.

Stanny · 02-17-08, 07:50 AM

Actually,there are such situations when both contacts are changing their bearings (shifting) after you complete a turn of the ownship.

I tried out making such resolution turns while looking at TA narrowband waterfall displays.The only difference you can notice between two equal contacts is that one is shifting more degrees than another.For example,one was assigned at 255 and shifted to 259,other was assigned to 166 and shifted to 163.There is a difference 4 Vs. 3 between the change of both contact bearings,and I think that contact that shifts less is a true bearing.

We do not have such a clear picture of what is going on in narrowband,unlike broadband where there are two visible lines on waterfall displays.We can only use tracker review button in order to see what happened to each contact,whether it changed it's bearing or not.

02-16-08, 05:28 PM	#4
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,904 Downloads: 304 Uploads: 0	To answer the initial question on solving the bearing ambiguity: 'Wag your tail' Sorry guys, a layer is not going to differentiate between two bearings. If you change depth the sound on both directions are going to disappear simultaneously. Because it is the same sound. It's just that the TA sensor can't tell the difference between left and right. I know, it sounds stupid with all that modern technology. But it is just the physics/math of it. And a uuv solution is way to expensive resource wise. Turn to a different course (a couple of tens of degrees to show it good) and see the mirror 'not real' contact shift in bearing twice as much as the course change (eventually). Since the angle between your tail (TA) and the true contact changes, the angle to the mirror contact must match (on the other side) after the turn. Which causes the sound to appear from a different direction twice as far. This link shows a picture why it can't tell left from right (about 80% of the page down): http://www.fas.org/man/dod-101/navy/...ys/asw_sys.htm Last edited by Pisces; 02-16-08 at 06:19 PM.

02-17-08, 06:11 AM	#6
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,904 Downloads: 304 Uploads: 0	Allright, I missed that part about his course change then. Also I'm sorry if I sounded a little tough. Bad excuse, but it was getting late. Anyway, I think he is getting confused on what the narrow band suite is showing him. The top window shows frequency(horizontal) versus time(vertical) of only one bearing out of 360 degrees. This bearing is selected by clicking and moving the cursor in the bottom window. That one shows signal level(vertical) versus bearing(horizontal). As long as the cursor in the bottom windows stay put the top window can't show sound from other directions. The middle window is only showing what the sound ID database thinks it hears. You can ignore that for now if you only have 1 or 2 lines. On the bottom window only loud contact stand out as a peak. You won't notice silent subs in that wobbly noisy graph. But they are there. You do scan a bearing in it, but only look for evidence of a contact by looking for lines in the frequency window. Those are not going to wave left or right, just fade-in or -out. When he found a 50hz signal on one bearing there should also be a 50 hz sound on a bearing that is "2xCourse - target bearing" (maybe need to correct by subtracting/adding 360 deg) So if he's on course 38 and detects a contact on true bearing 178, the other signal is on 2x38-178=76-178=-102=258. Both bearings are equal distances to your course or TA direction. If you confirm there is a contact on 258 you write both down, or assign a tracker to each. I preffer the former, as there are only so many trackers you can assign (4), and paper is cheap. But assigning a tracker is best if you are learning, because you can see it happen on the map. Make sure you turn OFF auto-TMA before doing this, or that crew member will take away the fun. Now, do the turn (let's say 30 degrees, and atleast some 4 minutes after assigning the trackers because they need to average out or something) and wait until the TA is straigtened and has been towed past the turn end point. (this can take a long while if you are slow, do not extend the TA fully, a 3rd is enough most of the time) Then try those bearings again. Which one stayed put? (within a few degrees, as it may move on it's own if the turn and straightening took a long while) That is the true contact. Which one isn't there any more, that one is likely the mirror/fake contact. Last edited by Pisces; 02-17-08 at 06:26 AM.

02-16-08, 10:04 AM	#1
Stanny Loader Join Date: Jan 2008 Posts: 88 Downloads: 0 Uploads: 0	Thanks for advice,sonar732.My typical loadout for Seawolf is that one with emphasis on MK-48 ADCAP torpedoes (all tubes are pre-loaded with them).However,this time I have had to unload the tube during mission and reload it with only UUV.TASMs and TLAMs as well as all other gear are in stores. I never use TASMs against surface ships,actually,as every Tomahawk is usually met with heavy barrage of anti-aircraft fire.So,MK-48 ADCAP is my weapon of choice for antisubmarine or antiship missions.

02-17-08, 07:50 AM	#7
Stanny Loader Join Date: Jan 2008 Posts: 88 Downloads: 0 Uploads: 0	Actually,there are such situations when both contacts are changing their bearings (shifting) after you complete a turn of the ownship. I tried out making such resolution turns while looking at TA narrowband waterfall displays.The only difference you can notice between two equal contacts is that one is shifting more degrees than another.For example,one was assigned at 255 and shifted to 259,other was assigned to 166 and shifted to 163.There is a difference 4 Vs. 3 between the change of both contact bearings,and I think that contact that shifts less is a true bearing. We do not have such a clear picture of what is going on in narrowband,unlike broadband where there are two visible lines on waterfall displays.We can only use tracker review button in order to see what happened to each contact,whether it changed it's bearing or not.