I tried to calculate the intercalibration factor between the seismometer on the ground, and the F0 LVDT. However, given the current microseismic conditions, the LVDT does not seem to have enough sensitivity for this calculation.
The figure shows the TF from the seismometer to the F0 LVDT, the coherence and the ASDs of the readouts of both devices. Additionally, the readout of the SR3 F0 LVDT is also shown for reference (see entry 23093). Such a spectrum was measured simultaneously as the ones for SR2.
As can be easily seen in the plots, the coherence is only high within a very narrow frequency band, and only one of the three expected peaks is visible. Therefore, it does not seem possible to follow the procedure outlined in klog 22998, and used as reported in klog 23093 for SR3. The transfer function is supposed to be close to unity at high frequencies, a value that is highlighted with a horizontal red line.
The limitation is the poor sensitivity of the SR2 LVDT. In the case of SR3, it was possible to calculate the intercalibration factor because its LVDT is more sensitive and the three peaks were clearly visible. Namely, above 1 Hz, the sensitivity of the SR3 LVDT is 15 times higher than that of SR2; the first one reaches 2 nm/rtHz, whereas the second one only 30 nm/rtHz. These levels are indicated with horizontal red lines in the figure.
This is information on the Jupyter notebook and diaggui file I used:
- File name: seismometer_F0_lvdt_intercalibration.ipynb
- Directory: /kagra/Dropbox/Subsystems/VIS/vis_commissioning/sr2/IP_diag/SENS_corre/Vertical/notebooks/
- Conda environment: vishack.
- Diaggui file: sr2_seis2f0_tf_ol_221130.xml