Reports 1-1 of 1 Clear search Modify search
Detector Characterisation (Glitches)
direnzo, longo - 19:01 Thursday 12 September 2024 (65142) Print this report
Scattered Ligth glitches on September 9 and 12

Related to the recent bad weather conditions, and the consequent high level of microseismic noise, we've had other episodes of Scattered Light glitches. I report here the study of these periods, mainly to keep track of them and to be searchable in the logbook for future or more in-depth analysis.

Figure 1: Glitchgram of the strain channel between September 9 and 12 at 6:00 UTC, with the time series of the three axes of the Central Building seismometer reported below. At the extremes of this range, a high density of triggers (markers in the scatterplot) can be observed, coincident with the high amplitude of the rms signal of the seismometers.

Figure 2: Q-scan of the last hour before the unlock on September 12.  Several excesses of noise are visible. A few of them are particularly loud, such as those in Figure 3, with SNR > 1000; these could be analyzed with dedicated omicron scans (work in progress...). The vast majority of the glitches have much fainter SNR. Most of them resemble arcs in the spectrograms, therefore Scattered Light glitches. However, between 5:15:40 and 5:15:45 UTC, a dense band of glitches is noted (Figure 4), in which the characteristic shape of Scattered Light glitches is no longer identifiable. Investigations on this band are ongoing (maybe with a coherent analysis of this short segment of data...).

Figure 5: We performed the usual correlation analysis of Scattered Light glitches, already described in previous entries (#63761#64022 , ...), using all the raw channels with units of position, speed, and acceleration. The most correlated channels are all the position ones (from which the speed information was obtained). In the attached file all those with correlation larger than 0.3. The figure shows the most correlated channel, in a 10-second interval, where the overlap of the reconstructed scatterer velocity and the Sattered Light glitches can be clearly seen.  The result is similar to what was already observed in April and discussed these entries: #64022 and #64026.

 

Images attached to this report
Non-image files attached to this report
Comments to this report:
mwas - 20:14 Thursday 12 September 2024 (65143) Print this report

A few guesses without actually checking the data:

  • The short wideband glitches are due to photodiode saturation. In particular saturation of the audio channel of B1 PD1 and B1 PD2.
  • The noise periods are related to noise subtractions in Hrec being spoiled. The noise subtraction are refreshed every 240s from what I can read in the configuration. Which would explain the noisy block of data that looks ~240s long. During that time there will likely be more coherence with SRCL or MICH, and it would mean that the Hrec noise subtraction filters have wrong parameters during that time and add noise instead of removing it.
direnzo - 23:51 Sunday 15 September 2024 (65147) Print this report

I continue here the analysis of the loud (SNR > 100) glitches identified in the first post. Most of them appear to belong to the same family, characterized by a burst of energy of a few tenths of a second, with a peak frequency (the one typically reported in glitchgrams) between 10 and 30 Hz, and a broadband structure in which some resonances stand out, such as 74, 150, 500 Hz: Figure 1. Typically, these are frequencies where bilinear couplings are strongest and are excited in bad weather conditions. Compare, for example, the MONET results for September 12 (bad weather) and September 14 (calm) around the 74.4 Hz calibration line. At this link, you can find the omicron scans of some glitches belonging to this family.

In the hour of data shown in Figure 2 of the first post, there are also two glitches belonging to the 25-minute family, respectively at GPS 1410153390.86 (05:16:12.86 UTC) and 1410155120.89 (05:45:02.89 UTC), with a waveform clearly distinguishable from that of the other family: Figure 2.

I investigated Michal's hypothesis (confirmed by Didier during the DetChar meeting on Friday) about the coherence of LSC_MICH and LSC_SRCL during the period shown in figure 4 of the first post. Figure 3 and 4 show the coherence spectrograms between Hrec and LSC_MICH and LSC_SRCL respectively. As hypothesized, there is a band between 10 and 30 Hz in MICH with increased coherence between 5:16 and 5:20 UTC, and possibly again between 5:44 and 5:48 UTC. In SRCL instead a line is noted at about 19 Hz.

Finally, I add to the characterization of this period of bad weather the glitchgram and time series of the seismometers between September 12 and 13: Figure 5.

 

 

Images attached to this comment
Search Help
×

Warning

×