radar waves

[chiddler]

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Apparently when a radar gun is used, waves are doubly compressed (meaning doppler effect occurs twice). Why?

"the wave reflected from a moving object is in fact doubly compressed..."

 

[milski]

Stationary source to moving target - compressed once at the target. Then the target reflects the already compressed waves with the same frequency as it receives them. Target is moving towards the initial source, so you get one more compression when you receive them at the initial position.

 

[chiddler]

wait. a moment. thinking.

 

[SaintJude]

So, would the perceived frequency be 2x higher than in a regular doppler, or just slightly higher?

 

[milski]

So, would the perceived frequency be 2x higher than in a regular doppler, or just slightly higher?

Depends on how precise you want to be. The analytical solution shows it being slightly different, but for speeds significantly lower than the speed of light it will be virtually 2xΔf higher.

 

[chiddler]

ok i understand. thanks for your help.

 

[silverice]

problem solved..

 

[milski]

That's pretty much it. Keep in mind that in the first case you have stationary source and moving receiver while in the second it's a moving source with stationary receiver. With all that you should be able to calculate Δf for speed v if the speed of light/wave is c.

 

[milski]

problem solved..

You had a nice explanation, should have kept it here for the future readers. 😉

 

[silverice]

You had a nice explanation, should have kept it here for the future readers. 😉

LOL, I thought no one saw it. I was embarrassed cuz u answered the question with much fewer words. Mine was wordy, and wordiness can confuse ppl! as long as the question is answered😀