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Environmental Monitoring (Environmental Monitoring)
fiori, velcani - 17:10 Sunday 19 May 2024 (64283) Print this report
Human noise injection test

I had a look at data collected during the "human noise injection" test organized by the outreach team. The test consisted in a group of 30 visitors walking from the "flags" up to the CEB,  do some jumping and shouting in front of CEB, then going in and out of  the CEB (entrance room), then walking down towards the MC building and do again jumping and shouting in front of the MC building. The purpose of the test was to undestand what visitor tours are possibly allowed to do in periods of science data taking.

The test was performed on March 29, approximately between 17:12 UTC and 17:30 UTC.  When the test started the ITF was locked in LOW_NOISE_3_SQZ.

Figure 1 is a picture of the notes taken.

Figure 2 illustrates the locations and the actions timeline.

Figure 3 looks at some representative environmental sensors: seismometers on CEB and MC building floor, microphones inside the two halls. Shouts are weakly heard by microphones around 1kHz with sound level of mPa, as indicated.  Instead, jumps are clearly seen by seismic sensors, mainly in the vertical channel. The seismic signal of the jump near CEB is visible also in the seismometer of the MC building, and vice versa. Interestingly,  an excess noise is measured by seismometers about one minute before and one minute after the jumps (red boxes), which are likely associated to people moving to gather in proximity of the CEB (and then of the MCB), while right before and right after jumping people keep still for a bunch of seconds.

Figure 4 gives a look at the ITF status and sensitivity along the duration of the test.  The range drop at about 17:10 is due to one  25-min glitch. At about 17:16:40 a different glitch caused about 2Mpc drop. At 17:22:11 UTC the ITF unlocked. This glitch tentatively correlates to an excess motion of the IB suspension. At that time visitors were inside the CEB entrance room (17:15:57 "entering CEB", 17:16:42 "all inside").

Figure 5 shows some selected signals along the duration of the test.

Figure 6 zooms in at the time of the "jump in front of CEB" (17:15:00-17:15:05). The jump is well detected by the Guralp seismometer on the floor next to BS (ENV_CEB_SEIS_V) and by the vertical geophone on the laser lab floor (SBE_EIB_GEO_ground_y). This jump did not produce visible effects on the interferometer.

Between 17:16 and 17:21 an excitation is clearly seen in some seismic monitors, mainly the horizontal ones: EIB bench, EIB floor, IB suspension F0, and it seems to notice also something in the PR F0. This interval is zoomed in better in Figure 7. The floor of CEB is clearly excited by a low frequency (< 0.1Hz range) oscillation. As already said, during this interval a glitch occurred in Hrec (Figure 4, at 17:16:40 UTC). During this interval the visitors were entering and then exiting CEB. It seems not reported when exactly all visitors were outside CEB, since the reported time 17:18:45 refers to "visitor exiting CEB".

Figure 8 zooms around the time of the unlock, at 17:22:11. Also shown here is the time of the "jump at the intersection" (outside of CEB) that occurred exactly at 17:22:20 as annotated, that is 9 seconds after the unlock. The unlock correlates to a drift of PR suspension, as indicated by Andrea Magazzù in, and also shown in Figure 8.  This PR drift seems initiated at about 17:22:08. Clearly it was not caused by the jump. I could not find in the seismometers any "kick" coincident to that time. It is possible that the unlock was consequent to some influence on the ITF global alignment initiated when the visitors were moving in and out of the CEB, but I cannot tell for sure.

Figure 9 shows some selected signals concerning the MCB. The IMC remained locked for the whole duration of the test. The Jump outside MCB is clearly seen by the seismometer on floor at 17:28:30 UTC. It did not cause a noticeable perturbation of the MC suspension.

Tentative preliminary conclusions: entering the CEB building onsets low frequency oscillations sensed on CEB floors which can have deleterious consequences (glitch and unlocks); moving in the proximity of CEB produces for sure an excess noise of CEB floors, but it seems limited to the 1-5 Hz range and not inducing low frequency motion. The ITF unlocked when people were outside the CEB building but still in proximity, I cannot tell if that wouln't happen if they wouldn't have entered inside. The MCB is a safer place.


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fiori, ruggi - 18:11 Tuesday 21 May 2024 (64318) Print this report

As Paolo pointed out,  the PR drift that caused the unlock during the human noise injection test was most likely uncorrelated with the visitors presence, being instead one of the infamous "PR trips" affecting the ITF in those days (Figure 1) and

On the other hand, the presence of people inside the CEB caused, as reported, noticeable drifts of suspensions (in particular IB suspension drifted by more than 20 micrometers) which cannot be tollerated. As reported, the presence of groups of people outside but in proximity of CEB causes an increased seismic noise in the approx. 1-5Hz band, which is presently suspected to correlate with excess noise in B1:

The conclusion is that, at least in the present ITF condition which is paricularly sensitive to anthropic seismic noise, the presence of visitors groups close to CEB while in science data taking shall be avoided.

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