J. Kissel

More evidence of non-linear scattered light being a problem for the low-frequency sensitivity of the IFO, I show a trend of each translational DOF of the 3-10 Hz BLRMS velocity of the ground (as reported by the ITMY GND STS, in the PEM stay-clear zone of the H1/H2 bier garten) vs. the Binary Nuetron Star range. There is clear correlation between the two. The levels of in BLRMS that show correlation are roughly ~100-200 [nm/s] RMS or ~1-5 [nm] RMS. I also show trends of the same BLRMS band for the ISI ST1 T240s and ST2 GS13s in the Z direction. While the overall amplitude is reduce by an order or two of magnitude, the variation remains identical to the ground. 

@LSCFellows, @DetChar -- it would be good to do some scattering fringe studies e.g. LHO aLOG 22405 comparing how the speed of each chamber's isolation platform (as measured by T240s and/or GS13s) relates to the various BLRMSs of the DARM spectrum. 

This may also have to do with Robert's recent discovery of problems with the ITM elliptical baffles -- see, e.g. LHO aLOG 31886. Remember that the 3-10 Hz band cover's the HEPI Crossbeam Foot resonance (see LHo aLOG 13505 and G1401167), so ground motion is amplified in this region. 

And just in case anyone want's to blame the changes in BNS range on fluctuations in optical gain due to slow alignment drifts or other optical plant changes, I attach a trend of the relative optical gain. There is no correlation there.