TMA and range determination

[Troels K]

Hi

I’m new to Dangerous waters.

I’m having some difficulties determining the correct range to a contact.

At the moment I’m using active sonar to find the range. However, it would be nice if the range could be found without active sonar.

Therefore, how do you guys determine a suitable range to a possible target?

I know the basic TMA like lead/lag course, but the manual says that two or tree legs will result in a single possible solution (page 5-22), these two or tree maneuvers confuses me.

This is probably a huge subject, however, some short guidelines would also be appreciated.

Thanks in advance.

Troels

[MaHuJa]

The easy way out, is to use the autotma. Given enough time, it'll give you a dead-on solution.

Manually, things are a bit more complicated. But all in all, the extra legs are pretty much a requirement. It's a bit hard to explain, at least without illustrations, but there is a saying of sorts; that a change in bearing rate is needed for a good solution. By changing your own course or speed, you're forcing that bearing rate change. The more radical the change, the better.

Personally, I only exceptionally start working on a solution before well into a second leg.

[Sonoboy]

If you can, assign trackers to that contact on both the towed and spherical arrays. Then, in TMA, where the two different lines converge is a good approximation on the range of the contact.

[Troels K]

Thanks for the replies

MaHuJa:
The thing I don’t get is, how do I use a change in bearing rate to estimate the range?


Sonoboy:
Good advise I will try that.

Troels.

[Henson]

If you understand the difference between overlead and lead lines of sight, turning from an overlead to a lag or vice verse will provide you with both a minimum and maximum range.

[Henson]

Originally Posted by Troels K

MaHuJa:
The thing I don’t get is, how do I use a change in bearing rate to estimate the range?

A higher bearing rate will produce a greater bearing 'fan' which will limit the ranges based on an assumed speed. The lower the bearing rate, the greater number of possible rangees for a given speed (ie max range is greater).

There is also some funky math you can do to get range from ownship maneuvers, but I'm not sure I can post that here. I'll check.

[SKeeM]

Originally Posted by Sonoboy

If you can, assign trackers to that contact on both the towed and spherical arrays. Then, in TMA, where the two different lines converge is a good approximation on the range of the contact.

This is the best way to get range. If you can pick up your target on more than 1 sensor and then merg them to form a master contact. At that point you have a good range.

[Molon Labe]

Originally Posted by Troels K

Thanks for the replies

MaHuJa:
The thing I don’t get is, how do I use a change in bearing rate to estimate the range?

You'll notice the difference at the TMA stations as you attempt to find a solution. On the first leg, the bearing fan created is next to worthless because you can find so many vastly different solutions that fit the data. When you make a second leg, your ships contribution to the bearing rate is different, which means that most of the solutions that you looked at during the first leg will not fit the data from the second leg, leaving you with a much smaller set of possibilities. If you can learn, or at least reasonably estimate, the target's speed, the number of valid solutions begins to approach 1.

[Troels K]

Once again, thanks for the replies, my TMA has improved significantly.

Originally Posted by Henson

There is also some funky math you can do to get range from ownship maneuvers, but I'm not sure I can post that here. I'll check.

Sounds good, I hope it's possible.


Best regards.

Troels

[Henson]

Google Ekelund range. You can find this on the internet, but you'll have to dig.

Considering where I got this formula I'm still not comfortable with repeating it in an internet forum, but that seemed a good compromise. There a re a few technical papers that wil take you through the process. It basically uses bearing rate and a change in the line of sight to determine a best estimate of range.

[OKO]

Originally Posted by Molon Labe

You'll notice the difference at the TMA stations as you attempt to find a solution. On the first leg, the bearing fan created is next to worthless because you can find so many vastly different solutions that fit the data. When you make a second leg, your ships contribution to the bearing rate is different, which means that most of the solutions that you looked at during the first leg will not fit the data from the second leg, leaving you with a much smaller set of possibilities. If you can learn, or at least reasonably estimate, the target's speed, the number of valid solutions begins to approach 1.

you have all in that short but accurate description

I just mention one more thing : during the record of the LOBs (line of bearing) your sub must NOT change depth/speed/course, or you will generate corrupted LOBS

so, in resume, you will have a first "pure" leg of 3 or 4 LOBs (preferably 4), thenyou will change your course and you will have 1 or 2 corrupted LOBs (NOT to use in the dot stack because they are corrupted) then again 3 or 4 LOBs on the second leg, after your course change.
then you will align the first 4 and last 4 LOBs on the dot stack, and if you have a good speed estimation of the target, the TMA become really accurate and quite easy.

The main and common problem is to start to work at TMA when you don't have enought information there.
It's totally useless to do that because you could have more than one solution and you could be desesperate to be unable to make the TMA.

So you have to wait the RIGHT TIME to start to work at this station
and the right time, if you make a TMA with a single array, is when you finished to record your 2 legs of data, NEVER before.
This "small" problem cause many people to think TMA is difficult when it is just not.

Basically, you should spend only some minutes per hour on your TMA station, and certainly not big time there.
But you have to start to work ONLY when it's time to do and certainly not earlier.

[Wim Libaers]

It would have been convenient to have a (time corrected) Ekelund or Spiess line calculator integrated into the TMA screen. You can do it now, but you need some extra tools (writing down bearings and rates often, programmable calculator), while all the necessary information is already in the TMA screen.

[SeaQueen]

Originally Posted by Wim Libaers

It would have been convenient to have a (time corrected) Ekelund or Spiess line calculator integrated into the TMA screen. You can do it now, but you need some extra tools (writing down bearings and rates often, programmable calculator), while all the necessary information is already in the TMA screen.

Oooo.... another good thing to stick in my spreadsheet...

[MaHuJa]

Getting the bearing rates in the sonar stations on the subs alone would help a lot there.


Anyway, the thing I said applies for general solutions as well - it's through the effect the second leg has that you can vastly reduce the number of solutions.

[sonar732]

I can still remember ultilizing the "wheel" for basic TMA while in sonar A school.

Place data #1 in outside wheel...turn for data #2....mmmm...Look at your crude drawing of LOS...