Debasmita, Preeti, Gaby
Robert did some injections at 0.2 Hz in the BS HEPI which showed a slight increase in DARM. We wanted to check further if the microseismic ground motion (0.1-1.0 Hz) is creating any noise in LHO as it does in LLO. For this, we chose the glitches in DARM picked up by omicron, having frequency in the range 10-60 Hz and SNR in the range 5-20.
- The first image shows the variation of glitch rate and the microseismic ground motion during December 2024. It looks like the glitch rate was higher on the days when the microseismic ground motion was high.
- The second image shows a scatter plot of glitch rate vs ground motion and from this we can see a correlation between the two.
- We calculated the Pearson and Spearman correlation coefficients between the glitch rate and the microseismic ground motion in two frequency bands 0.1-0.3 Hz and 0.3-1.0 Hz. The correlation values are tabulated below. Ground motion in both the bands show good correlation with the glitch rate. But, the ground motion in 0.1-0.3 Hz is better correlated with the glitch rate.
| glitch rate vs ground motion in 0.1-0.3 Hz | glitch rate vs ground motion in 0.3-1.0 Hz | |
| Pearson correlation coefficient | 0.605 | 0.472 |
| Spearman correlation coefficient |
0.602 |
0.439 |
- The third image shows the frequency and SNR distribution of the glitches that we chose. There are a total of 11111 glitches.
- The fourth image compares DARM spectra during a quiet time and a time of high microseismic ground motion and there are some excess noise visible during the latter.
The attached pdf shows qscans of some of the glitches chosen from high microseismic days. It is not very clear from the qscans if the glitches have arch like morphology, which is usually the case for glitches caused by scattered light. But, some of the glitches do show repetition within short time interval which make us suspect if they are produced by scattered light. We are still working on this to figure out if it is the process of scattering which is upconverting the low frequency ground motion to create noise in the 10-60 Hz band.
In summary, it looks like the microseismic ground motion is affecting the DARM sensitivity at LHO, maybe not as much as it does at LLO.
