= ETMY, geophone calibration =
-- Three geophones for ETMY suspension were calibrated using one geophone which had been already calibrated with seismometers. This test was ongoing at SR area.

== Procedure ==
-- In this work, the newly assembled geophones were labeled: geo-21, geo-18, geo-23, while the reference was named geo-5, which is for SR2 suspension.
-- In order to get the transfer functions from geophone raw signals to velocities, (1) was measured for each geophones and those transfer functions were fitted with (2):
  (geo-{21/18/23}-raw ) / (geo-5-vel),  -- (1)
  (preamp_gain*Ge*w*w) / (w0*w0 - w*w + 2.j*eta*w0*w),  -- (2)
where preamp_gain is equal to 375.53*5./2 = 938.825, Ge denotes generator constant [V/(m/s)], eta is intrinsic damping ratio, and w0 is resonant angular frequency [rad/s]. (see [1])
-- measured data in time_series / frequency as in 1st pdf (range from 0.2Hz to about 30 Hz were concerned here.) 
-- 2nd pdf show the fitting results,
-- using the information in the 1st pdf, the noise levels were estimated with 3-channel correlation analysis as in 3rd pdf.
-- checked the calibrated geophone signals were consistent with the seismometers in the center area, at IMC area, as in 3rd pdf.

-- These calibration factors will be installed after a cehck after closing the flanges.