LLO has been trying ground STS feed forward to HAM4 (Rana's alog ). I attach some spectra here suggesting we may want to try it as well. First plot is the coherence between the ground STS and SRCL_CTRL, red and blue are during a lock on Feb 14, green and brown are from a lock this afternoon. Even though our microseism is a factor of ~20 lower than it was during the lock in February, there is still some coherence between the Z STS and SRCL. The second plot shows the ITMY Z (in nm/s) and SRCL_CTRL (don't know the units here) spectra for both locks. The last plot shows the transfer functions from the STS to SRCL, red and blue are February, green and brown are today, looks like the coupling doesn't change much even with very different ground inputs.