Anna Kurzych

Fibre Optic System for Monitoring Rotational Seismic Phenomena

We outline the development and the application in a field test of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of the seismic-origin rotations of the ground. The main advantage of AFORS is its complete insensitivity to linear motions, as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas the applied telemetric system based on the Internet allows for an AFORS remote control. The laboratory investigation of such two devices indicated that they keep an accuracy of no less than 5.1 × 10−9 to 5.5 × 10−8 rad/s in the detection frequency band from 0.83∼106.15 Hz and protect linear changes of sensitivity in the above bandpass. Some experimental results of an AFORS-1 application for a continuous monitoring of the rotational events in the Książ (Poland) seismological observatory are also presented.

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising. It is shown that optical rotational seismometer based on the ring-laser gyroscope concept is the best for seismological applications, whereas systems based on fiber-optic gyroscopes demonstrate parameters which are also required for engineering applications. Laboratory results of the Fibre-Optic System for Rotational Events & Phenomena Monitoring using a small 1-D shaking table modified to generate rotational excitations are presented. The harmonic and time-history tests demonstrate its usefulness for recording rotational motions with rates up to 0.25 rad/s.

FOSREM: Fibre-Optic System for Rotational Events and Phenomena Monitoring: Construction, Investigation and Area of Application

This paper reviews our expertise with construction, investigation and simulation of the fibre optic interferometric device named FOSREM (Fibre-Optic System for Rotational Events and Phenomena Monitoring). The presented device was designed for a direct monitoring of rotational components emitted during seismic events as well as existing in irregular and complex structures. The construction of the FOSREM utilizes the Sagnac fibre interferometer in a minimum optical gyro configuration. This approach causes that FOSREM is complete insensitivity to linear motions, and it enables to measure directly the rotational components. In order to make FOSREM mobile and autonomous device we were focused on decreasing size to the 36 × 36 × 16 cm dimension and implementing special FORS – Telemetric Server which enables to control FOSREM remotely via Internet. The laboratory investigation of our system indicated that it keeps the theoretical sensitivity equal to 2·10−8 rad/s/Hz1/2 and accuracy no less than 6·10−9–5·10−5 rad/s in a frequency band from 0 Hz to the upper frequency between 2.56 and 328.12 Hz, respectively. FOSREM protects linear changes of sensitivity in the above detection frequency bandpass and has the maximum values of rotation rate possible to record without “overshoot” equal to 10 rad/s due to an innovative electronic system.

Devices for a Rotational Ground Motion Measurement

Generally, a rotational ground motion can be induced by earthquakes, explosions, and ambient vibrations. From the above point of view, it is interesting for a study concerning the area of rotational seismology (Lee et al. 2009a).

Fibre-optic gyroscope as instrumental challenge for rotational seismology

Rotational Seismology caused highly interest in investigation of rotational movements generated by earthquake, mines and existing in engineering structures. The most oppressive aspect of research in this field is technical requirements for sensors. However, the instruments basing on the Sagnac effect seem to be the most appropriate to investigate rotational effects due to the fact that they are entirely insensitive to translational motion and are able to measure rotation rate in wide frequency and amplitude band. The paper presents a new device FOSREM which, based on FOG, possesses special solutions that makes it perfect, in author knowledge, for any rotation sensing.

Construction and laboratory test of the fiber optic rotational seismograph FOSREM for rotational seismology area of interest

A relatively young field of study named Rotational Seismology caused a highly interest in an investigation of rotational movements generated by earthquakes, explosions, and ambient vibrations. It includes a wide range of scientific branches. However, this field needs to apply appropriate rotational sensors which should fulfill restrict technical requirements. The presented in this work system FOSREM (Fibre-Optic System for Rotational Events and Phenomena Monitoring) seems to be a promising rotational sensor for such investigation. FOSREM works by measuring the Sagnac effect and generally consists of two basic elements: optical sensor and electronic part. Regarding to its theoretical sensitivity equals 2·10-8 rad/s/Hz1/2, it enables to measure rotation in a wide range of signal amplitude (10-8 rad/s ÷ 10 rad/s) and frequency (DC ÷ 328.12 Hz). Moreover, FOSREM is mobile and remotely controlled via Internet using a special designed software.

Construction and laboratory test of a fibre optic sensor for rotational events recording

We present a novel and technically advanced system – Fibre-Optic System for Rotational Events & Phenomena Monitoring (FOSREM). It has been designed in order to register and monitor rotational events in seismological observatories, engineering constructions, mines and even on glaciers and in their vicinity. Its wide application field is a result of unique parameters and electronic solutions which give an opportunity to measure a component of rotation in the wide range of a signal amplitude from 10-8 rad/s to 10 rad/s, as well as a frequency from 0 Hz to the upper frequency between 2.56 Hz to 328.12 Hz. Moreover, the numerical analysis and simulations indicate that it keeps the theoretical sensitivity equal to 2·10-8 rad/s/Hz1/2. FOSREM is equipped with an advanced communication module which gives the possibility for a remote detection parameter control, as well as the recorded data receiving. It enables the sensor to assemble in any chosen place. In the paper we present laboratory investigations and tests which confirm the wide application field and practical aspects of FOSREM.

AFORS - Autonomous Fiber Optic Rotational Seismograph as a System for Continuous Monitoring the Rotational Seismic Events

We outline the development and application of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of seismic rotation. The main advantage of AFORS is it complete insensitivity to linear motions as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas applied telemetric system based on the Internet allows for a remote AFORS control. The laboratory investigation of the two such devices indicated they keep accuracy no less than 5.1·10-9 to 5.5·10-8 rad/s in the frequency bandpass from 0.83 Hz to 106.15 Hz with protect linear changes of sensitivity in above bandpass. The experimental results of AFORS-1 application for continuous monitoring the rotational events in the Książ (Poland) seismological observatory are also presented.

Application of the fibre-optic interferometer as a rotational seismograph type AFORS

In this article we show a fibre-optic device based on the Sagnac effect designed for measuring rotational motions which appear during seismic events. The experimental investigations of presented Autonomous Fiber-Optical Rotational Seismographs indicate that such devices keep the accuracy no less than 5.1·10-9 to 5.5·10-8 rad/s in the frequency band from 0.83 Hz to 106.15 Hz. Furthermore, their operations are controlled fully remotely via Internet. We present the comparison of results obtained by such system in the field test with a mechanical rotational seismometer which is mounted simultaneously in the seismological observatory in Książ, Poland.