Attachment #1 shows the spectra of our three available seismometers over a period of ~10ksec.

• I don't understand why the z-axis motion reported by the T240 is ~10x lower at 10 mHz compared to the X and Y motions. Is this some electronics noise artefact?
• The difference in the low frequency (<100mHz) shapes of the T240 compared to the Guralps is presumably due to the difference in the internal preamps / readout boxes (?). I haven't checked yet.
• There is almost certainly some issue with the EX Guralp. IIRC this is the one that had cabling issues in the past, and also is the one that was being futzed around for Tctrl, but also could be that its masses need re-centering, since it is EX_X that is showing the anomalous behaviour.
• The coherence structure between the other pairs of sensors is consistent.

Attachment #2 shows the result of applying frequency domain Wiener filter subtraction to the POP QPD (target) with the vertex seismometer signals as witness channels.

• The dataset was PRMI locked with the carrier resonant, ETMs misaligned.
• The dashed lines in these plots correspond to the RMS for the solid line with the same color.
• For both PIT and YAW, I am using BS_X and BS_Y seismometer channels for the MISO filter inputs.
• In particular for PIT, I notice that I am unable to get the same level of performance as in the past, particularly around ~2-3 Hz.
• The BS seismometer health indicators don't signal any obvious problems with the seismometer itself - so something has changed w.r.t. how the ground motion propagates to the PR2/PR3? Or has the seismometer sensing truly degraded? I don't think the dataset I collected was particularly bad compared to the past, and I confirmed similar performance with a separate PRMI lock from a different time period.