We generated the ground vibration noise by continuously tapping the PC table outside of the OMC booth.

We need more investigations, but just for memo.

Thank you for the detailed follow-up. By the way, when I had a discussion with R. Takahashi-san regarding the noise level of a usual geophone, the geophone's intrinsic noise might be larger than the usual gounrd motion in the ~100Hz freq region. Do you have any idea about the noise level of your measurement?

I'm not sure what is "the usual gounrd motion" you and Takahashi-san say, but if it is an  exploration from ~1 Hz, the actual (local) ground vibration over 20 Hz should be larger than it.

Yesterday I prepared many accelerometers for the OMC study.

Channel manes are the followings:

• 3-axial Seismometer (Trillium Compact) on the ground
  • K1:PEM-SEIS_OMC_GND_X_OUT_DQ
  • K1:PEM-SEIS_OMC_GND_Y_OUT_DQ
  • K1:PEM-SEIS_OMC_GND_Z_OUT_DQ
• Geophone on the in-vac table
  • K1:PEM-ACC_OMC_VACTABLE_OMC_Y_OUT_DQ
• Accelerometer (TEAC710) by a bellows leg
  • K1:PEM-ACC_OMC_CHAMBER_OMCLEG_Z_OUT_DQ
• Accelerometer (TEAC710) on the AS table
  • K1:PEM-ACC_OMC_TABLE_AS_Z_OUT_DQ 
• 3-axial Acellerometer (TEAC710Z) on the ground
  • K1:PEM-PORTABLE_OMC_RACK_OMC1_ADC0_DSUB13_OUT_DQ
  • K1:PEM-PORTABLE_OMC_RACK_OMC1_ADC0_DSUB14_OUT_DQ
  • K1:PEM-PORTABLE_OMC_RACK_OMC1_ADC0_DSUB15_OUT_DQ
• Accelerometer (TEAC710) on the Top range neck
  • K1:PEM-PORTABLE_OMC_RACK_OMC1_ADC0_DSUB16_OUT_DQ
• Accelerometer (TEAC710) for portable usage
  • K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC1_OUT_DQ
  • K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC2_OUT_DQ
  • K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC3_OUT_DQ
  • K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC4_OUT_DQ
     

Hmmm, so the invac geophone's spectral hill around 20-40 Hz range does not have coherence with the outer sensors...

We tapped the top flange of the OMC chamber to evaluate how mechanical vibration is propagated from the chamber to the in-vac table.

Fig.1 shows the ASDs of the accelerometer and the geophone, and their coherence. The geophone signal is converted from um/s/√Hz to m/s2/√Hz by multiplying 1e-6 * 2πf.
The unique structure around 20-30 Hz and 200-400 Hz in the geophone signal was not found in the accelerometer signal.
The coherence between these sensors was not so large except for some frequencies.

Fig.2 shows the transfer function from the accelerometer to the geophone, evaluated as CSD/PSD_ACC for coherence > 0.5.
The amplitude > 0 dB at the chamber's resonant?
 

We checked the effect of the trench (縁切り, we are not sure whether it actually exists) on the OMC chamber floor, using two accelerometers located on the outer and inner floors.

Fig.1 is tapping the outer floor and Fig.2 is the inner floor tapping.
For both cases, large coherence was found and the transfer functions from a tapped floor to another floor were about -10 dB at 10-100 Hz.

To distinguish whether a trench actually exists or not, we need to perform the same at another place where surely a trench exists.

Same work for the -Y side.

[Tomaru, YokozaWashimi]

We performed shaker injection tests for each bellows leg and evaluated the transfer functions from the witness accelerometers to the geophone.
(Single line injections for 25-40Hz and broad band injections for 40-600Hz)

Fig.1~3 are each result (ASDs, coherence, and transfer function).
Fig.4 is the comparison of each transfer function. They are roughly similar but the details are different.
The magnitude of the TF is largest at the "Leg5". (the injected vibration measured by the witness accelerometer for this leg was somehow smaller than that for the others.)
The magnitude of the TF is almost similar for all legs and any signature-flip was not found. (If the vibration (Y direction) on the in-vac table was tilt motion, the signatures for the "Leg1" and the "Leg5" are expected to be flipped. )

[Tomaru, YokozaWashimi]

We performed acoustic injection tests for the OMC booth and evaluated the geophone signal.

Fig.1 is ASDs and coherence for the geophone and the microphone signal.
Fig.2 is the estimated transfer functions.
Fig.3 is the comparison of the geophone signal and its acoustic noise (TF * MIC signal) for the non-injected data.

I moved the portable accelerometers to the OMC chamber body (top range neck)

+Y side, Z direction : K1:PEM-PORTABLE_OMC_RACK_OMC1_ADC0_DSUB16_OUT_DQ
+X side, Z direction : K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC1_OUT_DQ
+Y side, Y direction : K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC2_OUT_DQ
-X side, X direction : K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC3_OUT_DQ
-X side, Z direction : K1:PEM-PORTABLE_OMC_BOOTH_OMMT_BNC4_OUT_DQ
 

Fig.2 is the reference plots and Fig.3 is the plots during tapping the chamber.

I plotted the high-resolution (3-hour data, 128s FFT) ASDs and Coherences for the geophones and ACCs on the OMC chamber, for the night time before vacuum breaking.

sorry, the legend was clipped.

It is same for all plots.