# Light reflecting off of matte objects are subject to Doppler effects

Discussion in 'Physics & Math' started by RJBeery, Nov 24, 2011.

1. ### RJBeeryNatural PhilosopherValued Senior Member

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[Migrated from another thread at the request of a participant]
This discussion of microfacets on the cylinder is exactly why a matte surface (be it flat, round etc) cannot hide Doppler effects as it moves between a primary light source and a camera. I hear, very generally, the same thing coming from AN, Pete and Trippy, so I'm attempting to give my perspective with both visuals and math. (For Tach, this also addresses the "moved goalposts" of our debate, which apparently sit on casters

)

For a mirror whose orientation is parallel to its velocity moving between a single light source and a camera, the camera will ALWAYS detect the frequency emitted from the light source. This has been beat to death.

However, for a matte surface, the angle of incidence to the plane of the surface does not necessarily equal the angle of reflection away from it. This is due to the rough surface inherent in a matte material. The angle of incidence is equal to the angle of reflection against whatever the surface orientation happens to be at that point.

If we have $\phi_1$ = $\frac{\pi}{4}$ and $f_0$=550 THz, the plane of the matte object moving at $\frac{V}{c}$=.5 will "see" the light source as being roughly 305 THz.

In the case above, however, $\phi_2$ = $\frac{\pi}{8}$. This is trivially evidenced by the fact that a matte white wall is visible from all angles, regardless of the source of light. Therefore, using the formulas laid out here, $f_{s'}$ = 595 THz.

Summary:
$f_0$ = 550 THz
$f_{matte}$ = 305 THz
$f_{s'}$ = 595 THz

Conclusion:
Any surface with microfacets whose orientation is not tangential to its velocity from the frame of the camera will induce Doppler effects upon the light reflected to that camera. This includes mirrored washers, mirrored cylinders, and matte objects of all types.

3. ### TachBannedBanned

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What is the color of your matte surface or, alternatively, what is its reflection spectrum (expressed in Hz)? Without specifying the above, you have nothing.

5. ### RJBeeryNatural PhilosopherValued Senior Member

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OK...the matte surface is capable of reflecting light from 300-800 THz.

7. ### TachBannedBanned

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Then it is trivial, the camera frequency will be the source frequency multiplied by $\frac{1+v/c.cos (\theta_2)}{1+v/c.cos (\theta_1)}$.
If the surface is smooth, $\theta_2=\theta_1$
If the surface is rough, then the angles vary by as much as $\pi$ resulting into what is called "diffuse" reflection. I am quite sure I told you this before.
Is this the big discovery that you just made?

Last edited: Nov 25, 2011
8. ### RJBeeryNatural PhilosopherValued Senior Member

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Posted on 11-03-2011
My response...
It has taken you THREE WEEKS to finally see the truth. Listen, it's OK to be wrong about something, and it's even OK to be a bit arrogant, but your level of supreme arrogance mixed with being flat wrong and a sociopathic inability to admit it is sure to earn you little respect in this world. Can you not "feel" that you're probably less liked on this forum than even the biggest cranks?

Perhaps you should consider purchasing an armchair? :roflmao:

:thankyou:

9. ### TachBannedBanned

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Well, you are now studying a different case than the one that you self-destructed over in the debate. You got it wrong in the debate, so I let you self-destruct, you got it right now, so, I agreed with you. There is nothing that I can do for you, you are slowly learning the physics of reflection off moving bodies and this is good.

Last edited: Nov 25, 2011
10. ### RJBeeryNatural PhilosopherValued Senior Member

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Your misunderstandings three weeks ago, as evidenced by history, are indisputable; and your inability to manufacture ambiguity with my analysis today as you're still attempting to do with the debate topic (which you wrote) has you pinned in a corner...

I saw the truth almost immediately after you originally raised the subject. The big question is, what are you lacking that made the truth so difficult to see, and then after it was shown to you, so difficult to accept? Are you certain Physics is the right field for you? :shrug:

11. ### ReikuBannedBanned

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I'm sure I've seen you Rjbeery and a few other do this....

12. ### OnlyMeValued Senior Member

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Yea! Like Tach is ever going to end a discussion with the last line in that clip!

That would be admitting he... Was mistaken?

13. ### TachBannedBanned

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You described the scenario, all I did was to let you self-destruct. Your scenario, your equations, your errors. Why are you whining now?

14. ### RJBeeryNatural PhilosopherValued Senior Member

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Well my victory lap is usually much more dignified...what have I become? Perhaps it isn't too late for Pete, AN, Trippy and the others...

15. ### TachBannedBanned

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Well, this reminds me never to "wrestle" with you.