TMA Basics

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What is it ?

TMA (Target Motion Analysis) is the process that takes the information of all sensors to determine the position and the movement of a target.

Sensor Types

There are 3 different kinds of sources: Visual, Electro-Magnetic and Sound. All three have two types of operation: Active and Passive (the active visual method e.g. laser is not implemented). The active method sends out a signal and then listens for the echo (RADAR and ACTIVE SONAR). This way it can provide the target's bearing as well as the distance. (The distance is calculated by measuring the time between the signal and the echo.)
So the active sensors will actually give you the targets position but they will also tell everybody that you are there.
The passive method just listens for the signals the target emits (ESM and PASSIVE SONAR). Since you don't emit in this case you remain stealthy but you won't get (exact) distance information to your target just the bearing.
Obviously the Electro-magnetic sensors (ESM & RADAR) only work while the sub (it's antennas) are surfaced so we'll concentrate on the sonar part but basically it works in the same way as ESM and RADAR.

If you want to learn more about the sonar station check out the Sonar Pages.

SONAR Targeting

As mentioned earlier doing TMA with active sonar is fairly easy because it will give you the exact location of your target. So all you have to do is periodically ping your target, transfer it from the active sonar screen to TMA and voila you know where your target is and where it is headed. Of course things get a bit more difficult if there is more than one target around. Now you have to decide which target is your enemy and which targets are ADCAPs or other things. And of course your pinging will draw a lot of fire on you.
So if you want to remain stealthy you have to rely on your passive sonar to do TMA. Unfortunately passive sonar only provides you with bearing information. To estimate the distance to a target you have 3 possibilities:

Triangulation - if you extend you towed array it will give you a slightly different bearing information than your bow (or hull) sonar. Your target is where the two bearing beams intersect. This works best at close ranges with max. extended TA.
Estimate by signal strength - Obviously a target at close range is louder than one in the distance.. but there are a lot of other factors that influence this (target's speed, thermal layer...)
Observe the target for some time - If you track the target for some time you will notice a change in bearing and if you are able to determine (or estimate) the targets speed you can use this information to gather the targets position and motion during this process - this is what you would usually would call TMA.

Obviously a combination of all three gives you the best solution. So lets take a closer look on TMA. (Warning: some images ahead - about 50k each)