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Entry  Wed Dec 3 20:10:09 2008, Jenne, Rana, Update, PEM, Comparing Wiener subtraction with different seismometers Dec032008_c1wino_seisCombos.png
    Reply  Wed Dec 3 20:36:07 2008, Jenne, Rana, Update, PEM, Comparing Wiener subtraction with different seismometers d.pdfsco.pngfly.pdf
Message ID: 1173     Entry time: Wed Dec 3 20:36:07 2008     In reply to: 1172
Author: Jenne, Rana 
Type: Update 
Category: PEM 
Subject: Comparing Wiener subtraction with different seismometers 
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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