Paola is suggesting to use the OMC to control the CARM degree of freedom at low frequency (so use the OMC as a reference cavity).
Figure 1 shows the error signal of the two OMCs. In purple before the OMC dither reduced at the end of March, and in blue the current situation.
With the reduced OMC dithers the OMC1 error signal still sees the CARM motion below 1Hz but with a small SNR. With the larger dithers (which were not impacting the BNS range), the peaks of CARM motion are 2-3 orders of magnitude above the error signal noise. The dither could be increased for just one of the two OMCs, probably OMC2 that has a cleaner signal.