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 Wed Dec 3 20:10:09 2008, Jenne, Rana, Update, PEM, Comparing Wiener subtraction with different seismometers 
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 Wed Dec 3 20:36:07 2008, Jenne, Rana, Update, PEM, Comparing Wiener subtraction with different seismometers
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Message ID: 1173
Entry time: Wed Dec 3 20:36:07 2008
In reply to: 1172
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| Author: |
Jenne, Rana |
| Type: |
Update |
| Category: |
PEM |
| Subject: |
Comparing Wiener subtraction with different seismometers |
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The Ranger has now been moved over to sit underneath the MC2 tank (it was previously close to the PSL rack). It
is still pointed in the +Y direction (towards ETMY, aka south).
New spectra attached - looks like the coherence is still there between the Guralp and the Ranger which are now
seperated by the MC length (~12 m). At LLO, I have witnessed a coherence of less than 0.3 above 1 Hz for these
distances. Curious.
L960019-00-F describes measurements done at SLAC on seismic coherence. The iLIGO LSC PDD
(http://www.ligo.caltech.edu/docs/T/T970122-00.pdf) discusses in sec 4.2 how this was incorporated into the LSC design.
When we get our next Guralp, it will be interesting to move them around and determine what the cross-spectrum
is between different points in the lab during typical times.
In the second attachment, I have plotted the square of the quantity used in the LSC PDD (S_xy) which I think is
what we now plot in DTT as 'Coherence'.
The third attachment shows the coherences among the TM SUSPOS_INs. I've turned off the oplev servos for this but
the OSEM damping is still on. Its not quite the same as the theory, but we could probably measure/tweak the
seismic velocity and then get better agreement. |
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