To estimate in-loop MICH noise:

(a) Calibrate MICH_ERR:

1. Lock the arms for IR using POX11 and POY11.
2. Misalign the ETMs.
3. Obtain the average peak-to peak (bright to dark fringe) counts from the time series of AS55_Q_ERR. I measured this to be d = 6.358 counts.
4. This gives the calibration factor for AS55_Q_ERR [Calibration factor = 2*pi*d/1064/10^-9 = 3.7546x10^7 counts/m]

(b) In-loop MICH noise:

1. Lock MICH using AS55_Q.
2. Since LSC input matrix sets MICH_IN1 = 1* AS55_Q_ERR, the power spectrum measured using dtt and calibrated using the calibration factor from step 4 in (a) gives us the calibrated in-loop MICH noise.

The plot below shows the in-loop MICH noise and the dark noise (measured by closing the PSL shutter):

Compared with old measurements done by Keiko elog 6385 the noise levels are much better in the low frequency region below 100 Hz.
(No, no, no... this is not an apple-to-apple comparison: KA)