The sensor correction filter, reported in entry 23508, was designed using an upper limit of the microseismic motion (see 23507). It's fair to ask how such a filter would perform in different conditions, in case it's necessary to change its design. In this entry, I report the calculated noise of the corrected LVDT when the amplitude of the ground motion is low.
I used the ASD measured on the 28th of June 2022, when the secondary microseismic peak reached 0.25 um/rtHz approximately. The description of the figures is as follows:
- Low frequency noise empirical model (includes seismometer noise and ground motion too).
- Seismic noise, modified at low frequencies to be able to use it in the noise budget calculation.
- Noise budget calculation.
As can be seen in Fig. 3, the reduction of the rms noise of the LVDT is a factor of 4.4, integrated from 10 to 0.006 Hz, and the reduction of contribution of the secondary microseimic peak is substantial.
The calculation suggests that using this sensor correction filter, in these low amplitude seismic conditions, is not harmful for the performance, and it's even beneficial. It's worth pointing out that in these conditions, the ground motion is not expected to be a problem for the interferometer alignment even when the LVDT is not corrected.
