Summary - floating HEPI has significant improvements in the X and Y directions, the peak frequency of the effect shifts from ~11 Hz to ~8 Hz and reduces the magnitude of the resonance by ~an order of magnitude.

Thanks to Hugh, who put HEPI in all three states (see alogs - 13077, 13103, 13129), I've looked at the HEPI pier resonance at ETMY; I wanted to see the benefits of floating HEPI. I've taken one hours worth of recent data from when HEPI was locked/floating and compared the ground motion recorded by the STS2 (H1:ISI-ETMY_ST1_SENSCOR_GND_STS_X/Y/Z_FIR_IN1_DQ) to the top of the HEPI piers by the L4Cs (H1:HPI-ETMY_BLND_L4C_X/Y/Z_IN1_DQ). Attached is a plot showing the ASD ratio of the L4Cs to the STS2 for when HEPI is both locked and floating. Floating HEPI has significant improvements in the X and Y dorections only, the peak frequency of the amplification shifts from ~11 Hz to ~8 Hz and reduces the magnitude of the resonance by ~an order of magnitude. This is very similar to what we see at BSC1-3 at LLO (https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=13828). Comparing times when HEPI is locked, ISI is isolated and times when HEPI is locked, ISI St1 is isolated and St2 is damped do not appear to show much difference.

To see more on this study (and more plots) see: https://dcc.ligo.org/G1400820

NOTE - Data is still not being saved correctly to the H1:ISI-GND_STS_ETMY_X/Y/Z_DQ channels (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12818), hence why I've used the SENSCOR channels.