Today I measured the LSC sensing matrix, since cross-coupling is quite large, to the point where our feedforward to DARM is not working as well as it should. Evan and Sheila have taken this measurement in the past.  

We were locked on 22 watts input power after about a hour, so the IFO had thermalized.

I turned off LSC to DARM feedforward, turned on FM5 (EBS132) in MICH2, PRCL2, and SRCL2 to stop the drive signal from making it around the loops, then turned on a line at 132.1 Hz.  I measured by exciting the BS M2, PRM M3, and SRM M3 DRIVEALIGN L2L stages to avoid as many digital filters as possible.
-Drove BS M2 from 1223454828 to 1223456295 at 6000 cts.
-Drove PRM M3 from 1223452456 to 1223453337 at 1000 cts.
-Drove SRM M3 from 1223453571 to 1223454581 at 1000 cts.

I measured the output at H1:LSC-POP_A_RF{9,45}_{I,Q}_ERR_DQ, and the input at H1:SUS-{BS,PRM,SRM}_{M2,M3}_DRIVEALIGN_L_OUT_DQ.  I will calibrate the POP counts into watts later using Kiwamu's measurements.

I calibrated the suspensions from the point I injected to meters:
BS
BSFM M2 L2L at 132.1 Hz = 3.157e-12 m/N
M2 Coil Actuator Strength = 0.963 N/A
M2 Coil Driver = 0.327e-3 A/V
DAC = 20/2**18 V/cts
Total BS = 7.6e-20 m/cts

HSTS
HSTS M3 L2L at 132.1 Hz = 5.028e-7 m/N
M3 Coil Actuator Strength = 0.00281 N/A
M3 Coil Driver = 2.83e-3 A/V    (I believe this is 10x bigger than when Evan took his measurement, see alog 32021 and DCC G1100968)
DAC = 20/2**18 V/cts
Total HSTS = 3e-16 m/cts


POP9 was phased at -20.5 degrees, while POP45 was phased at -4.9 degrees.  POP9 digital gains were 8.0, POP45 were 1.41.  POP9 whitening gain was 12 dB, POP45 was 0 dB.

LSC Sensing Matrix
All units are POP ERR cts/pm

            POP9I      POP9Q      POP45I      POP45Q
------------------------------------------------------------
BS      |     528        385         275          42
PRM     |     357         68           6           1
SRM     |    1151        240          22           7


I have not yet altered the current input matrix based on these results.