[Shih-Hong Hsu, Chia-Jui Chou, Hirotaka Yuzurihara, Yi Yang]
In the study of scattered light noise, it is known that the scattered light noise is related to the seismic motion. In kagra, it is especially correlated with 0.3 Hz to 1 Hz (klog-33668). In this report, we check the coherence between the optical levers in PRCL (K1:VIS-PR{M, 2, 3}_TM_WIT_{L, P, Y}_DQ) and seismic motion near BS (K1:PEM-SEIS_BS_GND_{X, Y, Z}_OUT_DQ).
As a result, we found the length degree of freedom showed coherence larger than or close to 0.5 at 0.43 Hz for PRM, PR2, and PR3 with respect to x-direction seismic motion. The 0.43 Hz is chosen due to the frequency of potential scattering objects causing the scattered light noise (klog-33668).
Channels:
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OPLEVs: K1:VIS-PR{M, 2, 3}_TM_WIT_{L, P, Y}_DQ
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Seismic: K1:PEM-SEIS_BS_GND_{X, Y, Z}_OUT_DQ
Times:
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t1: 2025-07-15 11:00:00 UTC (1436612418) (larger seismic motion)
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t2: 2025-07-07 11:00:00 UTC (1435921218) (smaller seismic motion)
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Duration: 3600 s
Coherence:
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Gwpy: TimeSeries.coherence
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fftlength: 64 s
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Overlap: 32
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Marker: 0.43 Hz
Coherence at 0.43 Hz larger than 0.5:
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PRM_L-X: 0.579 (7-15)
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PR2_L-X: 0.914 (7-15)
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PR2_L-X: 0.893 (7-07)
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PR3_L-X: 0.871 (7-15)
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PR3_L-X: 0.721 (7-07)
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PR2_P-X: 0.795 (7-15)
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PR2_P-X: 0.689 (7-07)
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PR3_P-X: 0.648 (7-15)
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PR2_Y-X: 0.675 (7-15)
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PR2_Y-X: 0.669 (7-07)
Fig. 1: Seismic motion: K1:PEM-SEIS_BS_GND_Z_BLRMS_300MHZ1000.mean
Fig. 2~4: Coherence between PRCL OPLEVs and seismic X/Y/Z-direction for 0.3 to 1 Hz
