Performance and Laboratory Tests with a Prototype of FARO, a One-component, High-resolution Fibre Optic Rotational Seismometer

Classical seismometers cannot distinguish rotation from translation. Therefore, directly measured ground rotation can significantly improve quality of seismological data. To address this problem, a high-resolution rotational seismometer was jointly developed by Streckeisen GmbH, Swiss manufacturer of broadband seismometers, the Institute of Applied Mathematics and Physics and the Institute of Signal Processing and Wireless Communication both of the Zurich University of Applied Science, Switzerland. The one-component prototype called FARO is based on the principle of an open-loop interferometric fibre optic gyroscope. Key component is a coil with a fibre length of 20 km leading to a sensitivity of 5 nrads^-1Hz^-½ in a frequency range flat to velocity of 120 s to 50 Hz. It has a power consumption of 8.4 W and an input voltage range of 9 to 36 V. The prototype of FARO has a cylindrically enclosure with a diameter of 77 cm, a height of 28 cm and a weight of 27 kg.

Additionally, we present a self-noise comparison of various rotational sensors: the FARO, ROMY (the large ring laser gyroscope located at the Geophysical Observatory of the Ludwig-Maximilians University of Munich in Fuerstenfeldbruck, Germany), the BlueSeis3A (with a nominal self-noise level of 20 nrads^-1Hz^-½ , from iXblue, France) and a 150 m aperture array located around the ROMY ring laser.