Summary: We projected BSC2 SUSP motion as measured by ISI GS13's to the BBSS M1. This shows that seismic motion isn't enough to explain the excess QOSEM noisefloor.
This is one in a series of posts investigating the excess noise seen on the BBSS M1 QOSEMs. In short, at both LHO and LLO, the noisefloor of the QOSEMs appears to be around 8pm/rtHz at 100Hz, quickly increasing to 50pm/rtHz by 1Hz; where we expect the noisefloor to be flat at ~5pm/rtHz across this bandwidth. See more details in LHO alog 91466.
Here we look at the motion expected in the QOSEM readouts as driven by seimic motion coupling from the SUSP down into M1. Figures 1-6 attached below show the euler DOF readouts from the QOSEMs, compared against the motion measured at the SUSP by the ISI GS13's propagated to BBSS M1 using the suspension transfer functions. In these plots we see that Longitdualal SUSP motion has the largest contribution to the measured M1 motion, but not enough to explain the raised QOSEM noisefloor. With that said, these plots do show that ideally SUSP motion should be the dominant noise source for BBSS M1 below 10Hz.
This data was taken from LHO at T0=1470725000.
Hey Tom,
It's probably more useful to look at the SUSpoint to GAP rather than the SUSpoint to M1 inertial, where GAP is the thing the qOSEM is measuring, and is approximately M1 - SUSpoint. This should be pretty clean in vertical even though the cross couplings are complex for most other DOFs . Above a few hertz this will look like the ISI motion. The SUS models should make this pretty straightfoward. Also, maybe in scientific notation?