Starting from last Monday the SBE-SAT tracking is engaged on both Z and X axis of the SNEB and SWEB inverted pendulums. Profiting from the large variation in the microseismic activity in the last few days, and of the frequent downtimes of the ITF (the tracking is active only when the ITF is locked) it was possible to evaluate the performance of control. Here the main results:

• the plots in Figure 1 show the relative RMS velocity along Z between each bench and the nearby SAT; while SNEB clearly works better when the tracking in ON, SWEB seems to profit from the tracking rather marginally and its relative velocity figures are generally worse than in the other bench.
• the plot in Figure 2 shows a summary of the SNEB performance using as reference the in-loop geophones sitting on the inverted pendulum; the improvement in RMS displacement when the tracking is engaged are evident both in Z and in X directions.
• the plot in Figure 3 shows a similar summary done for SWEB; in this case only X improves with tracking, while Z is almost unaffected.

The fact that SWEB doesn't benefit from the better error signal available with the tracking points towards some mechanical issue (cabling or so) in the IP along the Z-axis. Further analysis of the data will be done to confirm this hypothesis.

The plot summarizes last week findings. The scattered light noise projections, made with seismic noise at 90 percentile, show that backscattered light from SNEB has a negligible effect on the sensitivity when tracking is active. In the case of SWEB, due to the unknown issues with the suspension, the benefit is marginal.