One of requirements of the ALIGO optical levers are to perform as well or better than their ILIGO predecessors in terms of sensitivity and their respective resonances.  I'm not sure of the state of the ILIGO optics during the measurement, but for ALIGO, we had the suspension damping loops running, the ISI damped, and HEPI locked.   Attached are 4 graphs comparing the ITM and ETM spectra from the LHO HIFO-Y test to Kate Dooley's spectra from ILIGO.  Both sets of data were calibrated to uradians so they should be directly comparable: 

- First off, we see that the sensitivity at frequencies >2Hz, the ALIGO sensitivity is better or the same in pitch for both ITM and ETM but yaw is not as good; the noise floor for ITMY pit is due to the ADC noise floor, as is true of the rest of the OL signals, but the other DOFS don't quite get down to that level of sensitivity till ~20Hz, this should be improved.  It looks like the noise is dominated by electronic that is ~1/f dependence, most investigation is needed.

- The good news is that the first resonances of the ILIGO piers occur at ~21Hz whereas the first ALIGO resonances that come from the pier peak at ~31 Hz, and keep in mind that this is done without grout which shown in ALOG 7746, will help push the resonant peaks higher in frequency.