Measurements of Rotational Events Generated by Artificial Explosions and External Excitations Using the Optical Fiber Sensors Network

Abstract

Measurements of artificial events can substantially confirm the data validity of constructed rotational sensors, as well as provide methods for simplifying the measurement process. The above task, especially with international cooperation, can provide full-field measurement results of the target object, which can deliver more significant data and sensor properties. The paper presents vertical rotational velocity recordings gathered during an international experiment that took place at the Geophysical Observatory of the Ludwig Maximilian University of Munich in Fürstenfeldbruck, Germany. Data were obtained during artificial explosions, as well as external excitations induced by a VibroSeis truck. The authors present data recorded by two prototypes of optical fiber rotational sensors. They have been specially designed for rotational seismology needs and are characterized by a theoretical sensitivity equal to 2 × 10−8 rad/s/√Hz and a wide measuring range both in amplitude even up to 10 rad/s, and a frequency from DC to 1000 Hz. Their self-noise investigation during the aforementioned experiment showed that both sensors have precision no worse than 2 × 10−6 rad/s/sqrt (Hz) in all desired frequency range from 0.01 to 100 Hz. A down-sampling and a spectral analysis of the recorded signals are also presented. The recorded data and their analysis confirmed the performance and reliability of the applied optical fiber rotational sensors. Moreover, the presented international experiment underlines a special necessity for specifying the sensors’ performance test methodologies in the rotational seismology.

Rotaphone-CY: The Newest Rotaphone Model Design and Preliminary Results from Performance Tests with Active Seismic Sources

“…The rotational components that were provided by Rotaphones in the array differed in peak amplitudes by 5% up to several tens of %, depending on the type of wave and explosion position. In fact, seismic rotational components can visibly change over a distance as short as, e.g., 2 m [ 3 ] or even shorter, as documented by other participants of the GOF experiment [ 34 ]. Firstly, this calls the frequent experimental arrangement of collocated rotational and translational measurements into question, where instruments stand side-by-side at some distance and not at exactly one point and, secondly, it reduces the informative value of comparative measurements targeted by the GOF experiment.…”

Opto-Electronics Review

“…The first published results cannot be regarded as a fully satisfactory comparison of data from different sensors, as it can be concluded from the fundamental Bernauer et al paper [14]. However, the separate data from different kind of rotational devices, including Rothaphone-CY [15] or FOS5 [16], show a "light at the end of the tunnel" regarding future harmonization of data collected by such devices.…”

Rayleigh-Wave Dispersion Analysis and Inversion Based on the Rotation

“…With the development of the rotational seismology, the joint use of translational and rotational components to detect the shallow shear-wave velocity structure has become one of the hotspots in the field of engineering and shallow seismic exploration [ 32 , 33 ]. Six-component (translational- and rotational-component) geophones and seismometers are gradually utilized in these fields [ 34 , 35 ]. However, rotational seismometers’ low sensitivity, large background noise, narrow frequency bandwidths, and high cost still limited their popularization and application [ 36 , 37 , 38 ].…”