Virgo Logbook

Detector Characterisation (Broadband noise)

verkindt - 18:15 Wednesday 17 July 2019 (46410)

Band rms in interesting frequency bands

Using the band rms, I looked at the noise level in h(t) in the following frequency bands: 20-70 Hz, 70-130 Hz, 130-160 Hz, 160-210 Hz over one week in May (plot1), in June (plot2) and in July (plot3).
The band rms covering the high 150 Hz peak (130-160 Hz) can vary by almost a factor 10; it was high in June and its current level is still about 3 times higher than its minimal value in May.
The band rms for 70-130 Hz is currently a bit higher than its value in June and May and is quite stationnary.
The band rms for 20-70 Hz is quite stationnary but with some local factor 2 increases (see for instance around 26th of June) maybe due to bad weather.
The band rms for 160-210 Hz is also stationnary and at a level a bit higher than the 70-130 Hz band rms.

The spikes in the plots are large frequency band glitches that, each time, cover more or less the frequency bands of the bandrms computation.

The commands used to do those plots are:
/opt/w3/vim/spectro/spectro_brms.C\(\"Hrec_hoft_20000Hz\",1242320000,700000,\"20-70\;70-130\;130-160\;160-210\",7e-24,1e-20\)
/opt/w3/vim/spectro/spectro_brms.C\(\"Hrec_hoft_20000Hz\",1245000000,700000,\"20-70\;70-130\;130-160\;160-210\",7e-24,1e-20\)
/opt/w3/vim/spectro/spectro_brms.C\(\"Hrec_hoft_20000Hz\",0,700000,\"20-70\;70-130\;130-160\;160-210\",7e-24,1e-20\)

I add plot4 and plot5 to add some info after Michal elog 46408.
They show the band rms in 60-90 Hz and 70-90 Hz bands over one week in June and in July.

Images attached to this report

Comments to this report:

direnzo - 19:56 Wednesday 17 July 2019 (46411)

The variations of the BLRMS in the region 130-160 Hz are largely due to the non-stationarities of the 150 Hz line, as it can be seen from some of the p-grams recently presented for stationarity studies. This issue could be also associaed with the huge amount of glitches detected when the BS is in drift control. I tried to rerun the BLRMS script exluding the 150Hz line and its sidebands. The result can be seen in the attached plot, where the BLRMS in the "background regions" of [130,145] and [155,170] Hz are approximately stationary for all th time of the study.

In general, the presence of strong, non-stationary spectral lines dominates the BLRMS in regions containing them.

Images attached to this comment

mwas - 20:14 Wednesday 17 July 2019 (46412)

Figures 4 and 5 are not very useful for understanding the noise behaviour between 60Hz and 90Hz. The effect we are looking for is a ~20% change in noise, but the figures span 3 orders of magnitude, so it is very hard to see any trend.

verkindt - 23:41 Wednesday 17 July 2019 (46416)

Plot1 and plot2 show a zoom on Y axis of the plot4 and plot5 of elog 46410, with linear scale on Y axis, so that we can see better the trend of the brms values.
I add also a plot showing those brms over all the may+june+july time period (plot3) and a zoom of it on the 60-90 and 70-90 brms (plot4).
For better reading, I add also a zoom over one month of such zoomed plot (plot5,6,7).

Finally plot8 is a zoom on a week of May where 60-90 brms had a large increase while the 70-90 brms had not.

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