Development of Three-Axis Fibre-Optic Seismograph for Direct and Autonomous Monitoring of Rotational Events with Perspective of Historical Review

The paper presents historical perspective of fibre-optic seismographs designed and constructed at the Institute of Applied Physics at Military University of Technology, Poland based on the so-called minimum configuration of fibre-optic gyroscope. The briefly presented history, which originated in the 1998 by the system named GS-13P, laid solid foundations for the construction of a three-axis fibre-optic seismograph. The presented system meets all technical requirements of rotational seismology in terms of measurement parameters (measuring range from 10−8 rad/s to several rad/s and frequency from 0.01 Hz to 100 Hz) and utility features (mobility, autonomy, power independence, environmental stability). The presented device provides universal application both for research in engineering applications (high buildings, chimneys, wind towers) as well as in seismological research

Investigation of rotational motion in a reinforced concrete frame construction by a fiber optic gyroscope

This paper deals with an issue of a rotational motion impact on a construction and presents civil engineering applications of a fiber optic rotational seismograph named Fiber-Optic System for Rotational Events & Phenomena Monitoring. It has been designed for a long- term building monitoring and structural rotations’ recording. It is based on the Sagnac effect which enables to detect one-axis rotational motion in a direct way and without any reference system. It enables to detect a rotation component in the wide range of a signal amplitude from 10-8 rad/s to 10 rad/s, as well as a frequency from DC to 1000 Hz. Data presented in this paper show the behavior of a reinforced concrete frame construction on different floors. Several measurements were carried out by placing the applied sensor on different floor levels of a building. The laboratory and in-situ measurements confirmed that Fiber-Optic System for Rotational Events & Phenomena Monitoring is an accurate and suitable device for applications in civil engineering

A test performance of optical fibre sensors for real-time investigations of rotational seismic events: a case study in laboratory and field conditions

Preliminary results of laboratory and field tests of fibre optic rotational seismographs designed for rotational seismology are presented. In order to meet new directions of the research in this field, there is clearly a great need for suitable and extremely sensitive wideband sensors. The presented rotational seismographs based on the fibre optic gyroscopes show significant advantages over other sensor technologies when used in the seismological applications. Although the presented results are prepared for systems designed to record strong events expected by the so-called “engineering seismology”, the described system modification shows that it is possible to construct a device suitable for weak events monitoring expected by basic seismological research. The presented sensors are characterized, first and foremost, by a wide measuring range. They detect signals with amplitudes ranging from several dozen nrad/s up to even few rad/s and frequencies from 0.01 Hz to 100 Hz. The performed Allan variance analysis indicates the sensors main parameters: angle random walk in the range of 3 ∙ 10−8–2 ∙ 10−7 rad/s and bias instability in the range of 2 ∙ 10−9–2 ∙ 10−8 rad/s depending on the device. The results concerning the registration of rotational seismic events by the systems located in Książ Castle, Poland, as well as in the coalmine “Ignacy” in Rybnik, Poland were also presented and analysed

Post-Processing of Raw Data Recorded Continuously Using a FORS—Fibre-Optic Rotational Seismograph

Modern optoelectronic devices use the advantage of digital systems for data processing aimed at delivering reliable information. However, since commonly used DACs have limited accuracy, some artefacts can be observed in data streams, especially in systems designed for continuous, long-term process monitoring. In this paper, the authors’ experience with data enhancement using a fibre-optic rotational seismograph (FORS) operating in a closed-loop mode is presented and discussed. Generally, two kinds of enhancement are described. The first one uses suitable filtering techniques adequate for FORS noise investigation, as well as a suitable data resampling method for transmitted data file size reduction. The second one relates to the artefacts observed during data recording in real time. The recording starting point is triggered when the detected signal exceeds a middle signal level and, therefore, the existence of artefacts generally disturbs the recording process. Although the artefacts are easily recognised by human eyes even at first sight, their automatic elimination is not so easy. In this paper, the authors propose a new concept of signal filtering to solve the above problem

Rotation, Strain, and Translation Sensors Performance Tests with Active Seismic Sources

Interest in measuring displacement gradients, such as rotation and strain, is growing in many areas of geophysical research. This results in an urgent demand for reliable and field-deployable instruments measuring these quantities. In order to further establish a high-quality standard for rotation and strain measurements in seismology, we organized a comparative sensor test experiment that took place in November 2019 at the Geophysical Observatory of the Ludwig-Maximilians University Munich in Fürstenfeldbruck, Germany. More than 24 different sensors, including three-component and single-component broadband rotational seismometers, six-component strong-motion sensors and Rotaphone systems, as well as the large ring laser gyroscopes ROMY and a Distributed Acoustic Sensing system, were involved in addition to 14 classical broadband seismometers and a 160 channel, 4.5 Hz geophone chain. The experiment consisted of two parts: during the first part, the sensors were co-located in a huddle test recording self-noise and signals from small, nearby explosions. In a second part, the sensors were distributed into the field in various array configurations recording seismic signals that were generated by small amounts of explosive and a Vibroseis truck. This paper presents details on the experimental setup and a first sensor performance comparison focusing on sensor self-noise, signal-to-noise ratios, and waveform similarities for the rotation rate sensors. Most of the sensors show a high level of coherency and waveform similarity within a narrow frequency range between 10 Hz and 20 Hz for recordings from a nearby explosion signal. Sensor as well as experiment design are critically accessed revealing the great need for reliable reference sensors.ISSN:1424-822