Over the last few days, we've been trying out the new 45 mHz blend filters for the BSC ISIs, which are designed to help out during times of high microseism.
This aLog is just meant to be a collection of logs relating to the switching, to help Team DetChar know which state things were in at which times, so they can hopefully make a comparison. One of the things that might be most interesting is the effect on the artifacts that Josh pointed out in aLog 22405.
Some of the logs that have talked about the switching back and forth include aLog 22440 and aLog 22459.
Looking at the SWSTAT of the ISI-[chamber]_ST1_BLND_[x or y]_CPS_CUR_SWSTAT channels I can see when the blends were in each state. FM7 is the nominal 90mHz blends (SWSTAT = 40000), and FM9 is the new 45mHz blend (SWSTAT = 40192). Below is a table of the lock stretches in each state.
| 90 mHz blends (nominal) | 45 mHz blends (new) |
| all locks through the one ending 10 Oct, 21:25 UTC | |
| 11 Oct 16:22 UTC - 12 Oct 18:11 UTC | |
| 13 Oct 00:53 UTC - 13 Oct 09:30 UTC | |
| 13 Oct 11:35 UTC - 13 Oct 14:43 UTC |
For some background, 45 mHz blends provide us with isolation at the microseism, which may be partially coherent between the buildings. When we lock with 90 mHz blends, we lock the position of the ISI to stage 0 at the microseism frequencies. With the normal seismic environment at LHO we find this better, because the interial sensors confuse wind induced building tilt with translation at these frequencies and if we try to use them to isolate they move the ISI in response to these spuirious signals.
In the fall, we tend to have less wind and more microseism, meaning that our seismic environment can sometimes be more similar to LLO's normal situation. Using the 45 mHz blends which are more similar to LLO's had allowed us to lock durring a high microseism, low wind time when we were unable to lock on our normal 90 mHz blends. We know that durring winds above about 20 mph we will be imposing spurious tilt signals on the ISI with these 45 mHz blends, which can make locking imposible or difficult.
So can you tell us the impact of these blends on DARM by comparing lock stretches with similar microseism and wind but different blends? It would be good to know this for a few different environmental conditions, (say winds below 15 mph and microseism high, and winds from 15-30 mph and microseism high).