Real navigation target motion analysis cheatsheet

[palmic]

Originally Posted by Xall

Hey palmic, I been trying to understand your methods, I been reading this one and trying to understand it, and I get stuck on one point, I am hoping you can help me with it.

So I will recap and show you how far I get.

First we have our course of 255 and our 3 bearings,

b1 = 71
b2 = 80
b3 = 87

each timed at 10 minutes in this case, while we are stationary.

Next we use your cheatsheet to find the cotangents,

cotan for b1 to b2 is 9 so we get = 6.3138 from your sheet,
and
cotan for b1 to b3 is 16 so we get 3.4874

so far so good.

next we have the formula

and this is where I cannot find out what the DRM is, direction of relative motion, is that not the angle beween our course and the target course? If so, how do we find the target course?

How do we find this?



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EDIT: I just read the conversation between you and hauangua, seems like he ran into the same confussion,

So what I understand is that, once you do the formula,
Cot(DRM -B1) = 2* Cot13 -Cot12 = 0.661

Then we Search in the cheatsheet for the closest value?
So in the Cheatsheet the closest value in this case is = 0.6644?

So 0.661 becomes 0.6644 which is = 56?

Am I understanding this correctly?

Hi Xall!
Sorry for my delay, i noticed right now.

Yes you have it right. Your targets DRM is 56.
Now you just have to subtract, or add it to first ABSOLUTE bearing.
Since your course in that time was 255 and the first bearing was 71, absolute bearing was 255+71=326.
Since bearings went up, you have to add, you would subtract otherwise.
So course of your target is 326+56=382=22!

For educative details about DRM please read the document from my initial post.

Just one more thing, you are unnecessarily too exact, round just to 1 decimal, your bearings from hydrophone and timing is the same unexact anyway and youll be surprised how exactly youll calculate even with one dec, its just way more quicker..

Happy hunting!