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Message ID: 6691     Entry time: Sat May 26 15:59:19 2012
Author: Den 
Type: Update 
Category: IOO 
Subject: Guralp noise is high 

As I've mentioned in yesterday's elog MC mirrors start to move in a synchronistic manner. I've plotted DELTA_GUR = GUR1_X - alpha * GUR2_X, where alpha = const to make the transfer functions SEISMOMETER -> ADC equal for each channel. I've noticed that DELTA_GUR decreases below 10 Hz compared to GUR1_X as theoretically predicted. But starting from 1 Hz DELTA_GUR starts to increase. I decided that this is Guralp noise floor. Today I checked this, this is indeed the case.

In the frequency range 0.01 - 1.5 Hz Gur noise is comparable to the signal DELTA_GUR. For that reason we see low coherence between MC_F and GUR1_X in this frequency range. 

gur_noise.png    MCF_GUR.png

Guralp noise floor was determined by placing 2 seimometers close to each other and subtracting by Wiener filtering.


Conclusion: To filter seismic noise out of MC_F we need more sensitive seimometeres.


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