Quote:
|
Originally Posted by Neptunus Rex
Incorrect. Doppler shift is solely a function of speed (own ships and/or target)in the "line of sight". Distance is not a factor. A measurable doppler shift at 5000 yards will be the same at 50,000 or 500,000 etc.
|
Doppler shift gives you the relative speed of the target.
You know your own speed so you can figure out the target's speed if you know the relative speed.
If you have the target's speed and the target's bearing rate, you have a good estimate of the target's range.
It's all about putting the pieces together. Knowing the target's speed can give you a pretty good range estimate very quickly. I don't know how much calculus you know, but here's how I think about it..
Pick a reference frame where you are stationary. In a very small instance of time, dt, your target (which is moving relative to you) travels a very small distance, ds. The target's speed v = ds/dt.
In that small instance of time the target's bearing changes by a small angle, dw. His bearing rate, BR = dw/dt. Now, by the definition of an angle, ds = R * dw. So, ds/dt = R * dw/dt. Therefore v = R * BR. So... R = v / BR. If you know the bearing rate and you know the speed, you've got his range.
You don't NEED to know his speed. You can do it with just bearings (see discussions of Ekelund ranging) but if you do have his speed, it's easy.
Ultimately it's all just your highschool geometry class.