Hirose, Tanaka

We installed the aluminum foil windshields on all oplevs of MC suspensions in order to reduce the air turbulence noise in their oplev signals. Fig1,2,3 are the MCI, MCO, and MCE oplevs before the installation, and Fig.4, 5 are the MCI, MCE oplevs attached to the shields (Sorry, we forgot to take a photo of MCO after the installation.)

After the installation, we measured the spectra of each oplev signal. Fig. 6 is the result, blue lines are the spectra before the installation, red lines are the one after the installation. As you can see, we succeeded to lower the air turbulence noise and some peaks can be observed in each oplev signal from 0.1 Hz to 10 Hz. 

Fig. 7, 8, and 9 are the time series during the installation for MCI, MCO, MCE. As you can see, the RMS of pitch and yaw signals seem to be lowered and the SUM values of each oplev seem not to change after the installation. Unfortunately, the values of pitch and yaw changed by up to 10 urads before and after the installation. Sorry about that. 

### some issues

In pitch signal in Fig. 6, the unknown peak is at about 4Hz. (we know the resonant frequency of Pitch is ~13 Hz and the one of YAW is ~ 2 Hz.) Now we have no idea about this peak... 

Fig. 10 is the spectra of SUM (K1:VIS-MC{I, O, E}_TM_OPLEV_TILT_SUM_OUT_DQ) and CRS (K1:VIS-MC{I, O, E}_TM_OPLEV_TILT_CRS_OUT_DQ) channels of each oplev. The signal of SUM looks generally good, but we can clearly see some peaks in the CRS signal of MCO. What does this indicate?