Correlation of phase for noise

[Joseph Warner]

Does anyone know over what distance or time the phase for
background noise from a blackbody is correlated on the long
wavelength side of the blackbody curve? The problem I am looking
at is that for an approximate plane wave on an antenna surface
over what distance is there any correlation of the noise. The
noise sources would cosmic background noise, sun noise, and
planetary surface noise. The frequency range would be from 1/2
GHz through 60 GHz; though, an data at a specific frequency even
if not within the range would be helpful.

I am not for certain how to apply the average transition time
between states to estimate the correlation time or length, and I
have not estimate on the average transition time. I would assume
most of the states would be rotational with some vibrational
states.

Thanks in advance for any help.

Joe Warner


[[Mod. note -- If discussion here doesn't suffice, you might try
re-posting your query to sci.astro.research. Disclosure: I am the
s.a.r deputy moderator.
-- jt]]

[Rich L.]

Joe,

I believe the answer really depends on the bandwidth of the detector.
The blackbody itself, being a wideband emitter, has very short
coherence time or distance if you are detecting all frequencies. What
you really need to know is the bandwidth of the detector, and what
coherence length and time that implies.

Rich L.

[Thomas Smid]

On 20 Oct, 19:37, "Joseph Warner" <Joseph.D.War...@nasa.gov> wrote:
> Does anyone know over what distance or time the phase for
> background noise from a blackbody is correlated on the long
> wavelength side of the blackbody curve? The problem I am looking
> at is that for an approximate plane wave on an antenna surface
> over what distance is there any correlation of the noise. The
> noise sources would cosmic background noise, sun noise, and
> planetary surface noise. The frequency range would be from 1/2
> GHz through 60 GHz; though, an data at a specific frequency even
> if not within the range would be helpful.
>
> I am not for certain how to apply the average transition time
> between states to estimate the correlation time or length, and I
> have not estimate on the average transition time. I would assume
> most of the states would be rotational with some vibrational
> states.
>
> Thanks in advance for any help.
>
> Joe Warner
>
> [[Mod. note -- If discussion here doesn't suffice, you might try
> re-posting your query to sci.astro.research. Disclosure: I am the
> s.a.r deputy moderator.
> -- jt]]


Hi Joe,

The spatial coherence is of the order lambda/D*R, where lambda is the
wavelength, D the size of the radiating source and R its distance. So
for astronomical objects, the coherence length should be much smaller
than your antenna, i.e. everything should be in phase across its width
(see

http://www.acs.ryerson.ca/~kantorek/ELE884/coherence.htm

or for a more detailed consideration

http://electron9.phys.utk.edu/optics421/modules/m5/Coherence.htm

note that the theory for the temporal coherence given on these pages is
actually not applicable to natural sources (which consist of a random
superposition of many radiators): as shown on my page
http://www.physicsmyths.org.uk/fourier.htm , the temporal coherence is
in this case simply given by the temporal coherence of the individual
emitters (e.g. the typical decay or collision time of an atom)).

Thomas

[Joseph Warner]

"Rich L." <ralivingston@sbcglobal.net> wrote in message
news:da08385e-0c5a-432e-8594-f4ae709cb306@k37g2000hsf.googlegroups.com...
> Joe,
>
> I believe the answer really depends on the bandwidth of the
> detector.
> The blackbody itself, being a wideband emitter, has very short
> coherence time or distance if you are detecting all
> frequencies. What
> you really need to know is the bandwidth of the detector, and
> what
> coherence length and time that implies.


Thank you Rich,

The bandwidth of the detector usually is limited to 1 to 5
percent of the center frequency.