Instrument self-noise and sensor misalignment

In this study we investigate self-noise of RefTekTM 151-60A "Observer" broadband seismometers (flat to velocity between 50 Hz down to T0=60 s, f0≈17 mHz) using the coherency analysis method introduced by Sleeman et al. (2006). We present a self-noise model for this type of sensor and compare it to the self-noise models of the standard observatory sensor STS-2 (Streckeisen) and RefTek's 151-120 broadband seismometer, which both have natural periods T0 of 120 s. We further report on the sensitivity of this technique to sensor misalignment and our success of eliminating leakage of the omnipresent microseism noise into self-noise estimates by numerically rotating seismic traces in order to find real self-noise.