J. Kissel, P. Fritschel,

Curious about the various features seen in Matt's spectra of the cavity length, Peter and I grabbed some data during the long stretch of cavity lock that Matt mentioned.

Attached are the results:
We show the ASDs of
- (What we believe to be) Ground Seismometer at IY, (we think) Y direction [(we think) uncalibrated]
- (What we believe to be) Ground Seismometer at EY, (we think) Y direction [(we think) uncalibrated]
- Input to the Isolation Filters of Stage 2 of BSC8-ISI (ITMY), Y direction in [nm/rtHz]
- Input to the Isolation Filters of Stage 2 of BSC6-ISI (ETMY), Y direction in [nm/rtHz]
- The input to the cavity control loop at the TOP / M0 of the H2 SUS ETMY, in L [uncalibrated]

and the coherence between all of the above with respect to the cavity length signal.

A couple of things that we can tell from these plots:
- The 0.12 Hz peak in the cavity L signal is most likely indeed just the micro-seism (even though it's incoherent with these Y direction sensors), because the frequency content of the ASD is roughly the same.
- The 1.05 Hz peak in the cavity L signal, which we believe is the second L/P mode of the QUAD, is NOT present in the ISIs or on the GND.
- The 0.43 Hz peak in the cavity L signal, which we believe is the first L/P mode of the QUAD, is also not terribly present in the the ISIs or the GND
- The BSC8-ISI (ITMY), which (we believe) has HEPI displacement sensor loops and high-blend ISI isolation loops, is directly, coherently transmitting ground motion into the cavity, as told by the coherence, between ~0.4 and 1.0 Hz -- and BSC6-ISI (ETMY) is not. I convinced myself that this made sense for BSC8-ISI (ITMY), because both the HEPI displacement sensor loops and the high-blend, mostly displacement-sensor-up-to-0.75 Hz, ISI loops are actively "locking" the platforms to the ground. The only sensible thing we could come up with for why the GND and ISI at the end were not coherent would be if the GND Y was not actually, as in the sensor was rotated, or we picked the wrong channel, or it was poorly labeled, or whatever. BUT that doesn't explain why the BSC6-ISI (ETMY) sensor was incoherent with the cavity length...
- It's confusing as to why the micro-seism is incoherent with everything.

Food for thought!

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Data is stored and committed to
/ligo/svncommon/SusSVN/sus/trunk/Common/Data/2012-07-10_H2OAT_ASDs.xml