This paper presents the development of a high-performance three-component fiber optic rotation seismometer (FORS) named DC-Rot3C for rotational seismic observation. Its core sensing element is a novel dual-channel interferometric fiber optic gyroscope (IFOG), which differs from conventional minimum configuration. The IFOG in DC-Rot3C is composed of two sensing channels, which can effectively suppress self noise such as relative intensity noise. This paper provides a detailed demonstration and analysis of the optical configuration, demodulation technology, layout construction, and noise suppression mechanisms of the developed DC-Rot3C. Furthermore, the performance of DC-Rot3C is tested, and the experimental results show that, with an effective sensing area of only 246m(2) , the self-noise remains flat from 0.001 Hz to 100 Hz, reaching a sensitivity of 6.2x10(-9)rad/s/root Hz. Additionally, the angle random walk (ARW) reaches 4.54x10(-9)rad/root s, and the bias instability (BI) reaches 2.96x10(-10)rad/s . Compared with other IFOGs and FORSs, the DC-Rot3C exhibits superior performance with the same sensing area, providing a high-precision tool for seismic observation.

The observation of the rotation of surface motion is of great significance in seismology. geophysics, engineering exploration, and other research fields, Interferometer fiber optic gyroscopes based on the Sagnac effect have attracted extensive attention in the research and development of rotational seismometers due to their advantages of all-solid-state, highly sensitivity and wide frequency response. To enhance the sensitivity of fiber optic rotational seismometers, long fiber loops are commonly employed. However, increasing the length of the optical fiber leads to thermal phase noise and relative intensity noise from the light source within the optical fiber loop, limiting their sensitivity performance. This paper conducts an in-depth analysis on the noises that degrade the sensitivity of fiber optic rotational seismometer. A dual-polarization configuration is proposed using the slow and fast axes of polarization-maintaining fibers and its optical configuration as well as demodulation algorithm are theoretically analyzed. The results show that the dual- polarization configuration can effectively suppress thermal phase noise and relative intensity noise. On this basis, a three-component dual-polarization fiber optic rotational seismometer DP- Rot3C is developed, and the static and dynamic tests are conducted. The results show that the sensitivity of the seismometer reaches 20 nrad center dot s(-1)center dot root Hz(-1), comparable to the French Bluseis-3A. It exhibits a flat response across a frequency range of 0.01 similar to 125 Hz and possesses a nonlinearity of less than 6ppm (1 ppm-0.0001%) over a dynamic range of 300 to +300 degrees/s. These results demonstrate that DP-Rot3C has high precision. wide frequency band, large dynamic range and high linearity. DP-Rot3C has been applied in multiple practical scenarios, including artificial active source observation, high-speed-railway seismology observation natural earthquake observation, and other fields. The above experiments indicate that DP-Rot3C provides a high-precision tool for observing the rotation motion for engineering exploration, seismological research, and other applications.

In recent years, with the development of rotation direct measurement instruments, rotational seismology has gradually become a hot field, and it is proposed that observation needs high sensitivity. The rotational seismometer based on fiber optic gyroscopes (FOG) has gradually become the preferred choice for seismic rotation observation due to its insensitivity to translational motion, fully solid state and high sensitivity. In order to meet the demands of multi station observation network in seismic exploration, the FOG which is the core sensing element of the rotational seismometer, needs to have the characteristics of high sensitivity and low cost. In this paper, a budget-friendly dual-polarization FOG scheme based on a Lyot depolarizer is proposed, and the ports difference method is employed to suppress the short-time noise and improve the sensitivity. The experiment adopts 2km polarization maintaining fiber ring, and the two ports have stable output. After the difference of the two port signals, the self-noise over 0.03Hz~50Hz is reduced from 260nrads-1Hz-1/2 to 120nrads-1Hz-1/2. It shows that the rotational seismometer using this structure has low cost and high sensitivity, and has a good application prospect.

Abstract A rotational seismometer based on dual-polarization interferometric fiber optic gyroscopes is designed and demonstrated, it can measure three rotation components at the same time. The angle random walk is about 1.67 × 10 − 4 ∘ / h . The self-noise ranging from 0.1Hz to 125 Hz is about 7.0 × 10 − 8 rad / s / Hz . It can be applied to seismic monitoring, seismic exploration, engineering monitoring and other fields.

Abstract The development of fiber optic gyroscope technology makes it possible to directly measure the rotational ground-motion. The joint observation of the three-component rotational seismometer and the traditional three-component translational seismometer is a trend of future. In this paper, the translational and rotational signals generated during the high-speed trainway are studied, and the three-component translational and rotational seismometers are fixed together to realize the joint recording of the high-speed trainway signal. Comparing the translational and rotational three-component data, we find that only one component waveforms and the spectrum have certain consistency. However, the difference between them indicates that the rotation and translation signals generated by the shallow surface wave signal have different frequency bands.

理论上,通过平移与旋转运动联合观测的六分量地震记录,在单物理点上即可实现浅层横波速度结构的反演.本文主要目的为结合正演模拟设计六分量面波数据处理的流程,并将此单物理点方法应用至广州市区所采集的数据当中.本次研究在正演模拟的阶段中,通过时频域滤波方法实现了基阶面波数据的提纯,设计了使用单物理点的六分量数据实现浅层横波速度结构反演的流程;在实际应用阶段,通过数据的波形和偏振分析,介绍了甲烷气爆震源激发下的六分量波场特征,并分析出基阶面波所在的时频区域,结合时频域滤波、基阶面波相速度反演得到了试验区的横波速度结构.其结果与区域地质调查结果有较好的对应性,说明此六分量地震观测方法在工程地震领域的应用是可行的.

With the development of rotational seismology, the observation of seismic rotational components deserves more attention in shallow engineering geological prospecting. In shallow seismic exploration, methane detonation source and electric spark source as new sources, and the characteristics of rotational motion under the excitation of these two vibroseises are worth studying. Based on the six-component seismic observation experiments of methane and electric spark sources in Guangzhou city and combining the experiments with numerical simulation of translational and rotational motions in a shallow 2-dimensional model, this paper proves that it’s feasible to capture the rotations induced by shallow engineering vibrations. By analyzing spectrum characteristics and particles polarization of the seismic data in different frequency bands and different frequency characteristics of these two sources, this paper compares the similarities and differences between translational and rotational components, and finds that rotational components can provide additional information different from the translational component and high frequency signals are more prominent in rotational components. Besides, river channel greatly diminishes the energy of surface waves below 10 Hz of observed data. These analyses indicate the characteristics and possible applications of surface waves in rotational components are so different from the ones in translational components.

The principle of dual polarized fiber optic gyroscope insensitive to the temperature and magnetic field variance is presented, and several novel experiments have been demonstrated, including earthquake detection, environmental noise recording and six-component seismograph.

Most of the previous seismic observation and analysis are still focused on the application of three orthogonal translation components. Because of lack of records of rotational motion, the seismic wavefield can not be completely described. We use an A-SM-2km rotation seismograph directly measure the rotation signals of ground motion and analyz them by short-time Fourier transform. The results show that the characteristic of the rotating component as the station spacing increase presents high-frequency attenuation.

For many years, seismological research mainly focuses on translational ground motions due to the lack of appropriate sensors. However, because of the development of devices based on Sagnac effect, measuring rotational waves directly comes available. In this work, a portable three-component broadband rotational seismometer named RotSensor3C based on open loop interferometric fiber optic gyroscope (IFOG) is designed and demonstrated. Laboratory tests and results are illustrated in detail. The self-noise ranging from 0.005 Hz to 125 Hz is about 1.2×10−7rads−1/Hz, and with the harmonics compensation the scale factor variation over ±250∘/s is lower than 10 ppm (parts per million). The misalignment matrix method is adopted to revise the output rotation rate. In a special near field experiment using the explosive source, the back-azimuths and phase velocity are estimated by the recorded acceleration and rotation rate. All the results prove the practicability of this new rotational sensor.