Plotting stationary targets while moving
 

I've been practicing my radar plotting with mobo overlaid on top of the PPI scope in SH4 and I'm confused about plotting stationary targets. How do you know you're tracking a stationary target while you're moving? Of course you could come to a dead stop to check but, without stopping how would you determine if your target is stationary if you plot multple nodes over time in an effort to find heading and speed as if you were tracking a moving target?

I haven't really used it much with the PPI scope, but Lurker did a tactical manual on how to use MoBo with the radar in SH4. It's a file in the download section under utilities.

In Lurkers example the vector addition of the target's relative motion resulted in the true motion of the target. In your case with a stationary target, I'm guessing the vector addition would result in zero speed.

Lurker is the expert, perhaps he could validate that for us? :hmmm:

Probably important to remember that plotting contacts on the PPI scope will always reflect relative motion and would always need to be converted to true motion. ...and that RM=TM only if OwnShip is stationary.

Perhaps this will help clarify...

Ownship is moving on heading 30° at 4kts
At 10:15 radar reports contact M1 at 36.0k yds bearing 270°R
At 11:00 radar reports contact M2 at 36.5k yds bearing 260°R

The plot looks like this:
http://www.xl-logic.com/mobo/tutoria...0090414_01.png

Connecting node M2 to M1 we can calculate the speed and direction of relative motion...
http://www.xl-logic.com/mobo/tutoria...0090414_02.png
We see above the speed of relative motion is 4.2kts over 45 mins.

The direction of relative motion is about 209°
http://www.xl-logic.com/mobo/tutoria...0090414_03.png
If we add Ownships vector to the contact's vector we'll see they negate each other and the resulting true motion speed is zero. You'd follow the same exact procedure for a moving target, only the resulting vector would have a speed and direction of true motion that would not be zero. The "Add Unit" tool in MoBo was created so you could easily do the vector addition.