We measured the ASC PIT Sensing matrix in the REFL sensors.

We drove cHard, cSoft, Inp1, PRC1, & PRC2 loops at around 8 Hz and then took data of the CHARD and REFL WFS signals. We started at 1150766030 and stopped at 1150766330. Coherence was > 0.98 for all elements of the matrix. But why? What's the point of all this? Well, we are trying to make a clean CHARD signal by mixing the REFL WFS signals. However, we have 5 DOFs that show up in REFL, but only 4 sensors.

Therefore this problem is not a pure matrix inverse. Moreover, we would like to maximize the SNR of CHARD in the CHARD_IN1 so as to reduce the CHARD controls noise injected into DARM. IF the REFL signals all had the same noise performance or if they were uncorrelated with each other, this would not be a problem.

The first attached image shows the spectra and coherence during the sensing matrix drive time.

The second image shows the co-Herence during the ~20 Mpc stretch from around 1 PM today. Of course, the ASC noise was really bad then, but its sort of always is, so...