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| Computers Forum Index » Computer - DSP » auto=correlation vs self-coherence... |
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| Author |
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| glen herrmannsfeldt... |
 Posted: Thu Sep 24, 2009 10:45 pm |
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Guest
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fisico32 <marcoscipioni1 at (no spam) gmail.com> wrote:
<>On Sep 24, 12:50=A0am, Rune Allnor <all... at (no spam) tele.ntnu.no> wrote:
<>> On 24 Sep, 04:06, "fisico32" <marcoscipio... at (no spam) gmail.com> wrote:
< It remains unclear to me if a perfect monochromatic signal is perfectly
< coherent but its autocorrelation is less than 1 for certain time shifts...
< correlation and coherence must be two different ideas...
I suppose so.
It seems to me that coherence only requires a constant phase
difference, where correlation (and autocorrelation) require
a specific phase difference.
It is less obvious for less than perfect signals.
If you have two sinusoids of slightly different frequency they
will have a coherence length (and coherence time) based on that
frequency difference. If, for example, you want to use a laser
for holography then the coherence length needs to be long enough
to allow for path differences across the object. Correlation
measures a somewhat different quantity.
-- glen |
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