I did a scattering scan for the entire site, including mid-stations, with a focus on the 50-200 Hz region and on sites that had previously been identified as potential scattering sites in scattering photos (e.g. https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=9564    https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=8281). The worst locations were between the chamber and the gate valve at the end stations (probably similar to what has been seen at LLO) and the input arm, especially between HAM2 and HAM3. The scattering at these three locations was close to showing, or showing in DARM, I can not be sure yet, study of these sites is ongoing. At EY I put black glass in each of the ports, which did not change the scattering peaks I was enhancing with a shaker. I thought the difference with LLO might be that there were no aluminum blocks in any of the LHO ports, so I inserted one in each of the ports but this did not make the coupling worse. We should try black glass at all ports simultaneously, and there are some other tests I would like to do.

At the input arm, the scattering noise, enhanced with a shaker, was clearly modulated with a 0.02 Hz yaw injection at PR2. I observed the input arm through multiple ports and found two spots that especially concerned me, both visible with the digital cameras after I adjusted them: the baffle in front of PRM (see photo) and around PR3.