Rotation sensing with fibre optic technology

Fibre-optic gyros (FOG) allow measuring rotational ground motions and have recently been the method of choice for a first-generation broadband sensor for seismology. FOGs have a unity transfer function, are insensitive to translations and – combined with broadband seismometers – allow exploiting the power of six-degree-of-freedom processing (6 DoF) methods. This includes phase separation, backazimuth and phase velocity estimation as well as tilt-correction. Recently, a permanent 6 DoF system has been installed at the Pinon Flat Observatory, California. We report on the observation of local seismicity and the detection limit of a commercial FOG. Furthermore we present results on 6 DoF observations on volcanoes, the estimation of 1D velocity models based on 6 DoF noise observations, and applications in structural health monitoring. Finally, we discuss the current limits of portable rotation instrument, and the future potential of 6 DoF sensing when the sensitivity is improved.