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The rotation rate of the Earth measured with the G ring laser as a function of time. Averaging over 2 hours was applied to a corrected dataset, where all known geophysical signals have been removed.
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Large scale square ring laser gyros with a length of four meters on each side are approaching a sensitivity of $1 \times 10^{-11}\, \mbox{rad}/\mbox{s}/\sqrt{\mbox{Hz}}$. This is approximately the regime required to measure the gravito-magnetic effect (Lense–Thirring) of the Earth. For an ensemble of linearly independent gyros each measurement sign...
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Context 1
... in fig. 3 are the effects from local tilt. These signals are non-periodic and usually change slowly over the run of several days. High resolution tiltmeters inside the pressure stabilizing vessel of the G ring laser keep track of these local effects and the data is corrected for gravitational attraction (atmosphere, sun and moon) and corresponding changes in the gravitational potential [9]. Local tilts change most prominently after abundant rainfall, indicating hydrological interactions with the rock and soil beneath the ring laser monument. The large seasonal temperature effect on the G ring laser as well as the substantial local tilt signals and the rather high ambient noise level of our near soil surface structures give reasonable hope of much better performances of a ring laser installation in a deep underground laboratory such as the Gran Sasso laboratory of INFN (Istituto Nazionale di Fisica Nucleare). For the detection of fundamental physics signals one has to remove all known perturbation signals of the Earth from the ring laser time-series. Furthermore we have applied 2 hours of averaging of the data in order to reduce the effect from short period perturbations. Figure 4 shows an example. In order to reduce the local orientation uncertainties, which remain after local tilts measured with the high resolution tiltmeters have been removed, averaging as indicated above was applied to a series of 30 days of data collection, including the period shown in fig. 3. It can be expected that a similar data set from the GranSasso laboratory would become substantially smoother, since most of the perturbations, caused by ambient atmosphere - topsoil interaction still contained in the data of fig. 4 would no longer exist in the deep underground facility. Changing hydro-logic fluxes presumably causing small local rotation, temperature variations, atmospheric pressure and wind loading are among the sources for the systematic signatures in the residual data. Despite the fact that large ring lasers are very stable platforms and with the provision of tight feedback systems to stabilize the scale factor (cold cavity, as well as the active cavity), currently ring laser gyroscope are not able to determine the DC part of the Earth rotation rate with a sensitivity compatible with the requirements for detection of the Lense-Thirring effect. While the contribution of the varying Earth rotation itself presumably can be removed with sufficient accuracy from the C04 series of VLBI measurements, there remains the problem of determining the actual null-shift offsets from the laser functions in the ring laser gyroscope. Since the gravito-magnetic effect is small and constant, a good discrimination against laser biases, such as for example ‘Fresnel drag’ inside the laser cavity must be achieved. Therefore it will be advantageous to add one or several ring laser cavities in addition to the triad structure for sufficient redundancy. We also intend to operate at least the G ring laser structure in parallel to the here proposed structure in order discriminate local perturbation signals from regional and global ones. A second large ring laser located at the Cashmere facility in Christchurch, New Zealand will be used in the data analysis process, provided it can be run with sufficient resolution and stability. We outline our first experimental design. Primarily this represents an attempt to obtain the required accuracy in the angles by using pairs of gyroscopes (twins), located astride the relevant positions and exploiting the possibility to reduce (by subtraction) the big slowly changing contributions while enhancing the weak terms whose sign changes on the two sides of the orientation which provides zero Sagnac. The experimental set-up is composed of a central rigid heavy body, called a monument, to whom all the gyrolasers are rigidly attached, fig. 5 shows the set up described here. The monument itself plays an important role in this experiment. In order to provide a measurement base, we propose to use a massive block of concrete as a stable central reference. Around this concrete foundation, we ...
Context 2
... in fig. 3 are the effects from local tilt. These signals are non-periodic and usually change slowly over the run of several days. High resolution tiltmeters inside the pressure stabilizing vessel of the G ring laser keep track of these local effects and the data is corrected for gravitational attraction (atmosphere, sun and moon) and corresponding changes in the gravitational potential [9]. Local tilts change most prominently after abundant rainfall, indicating hydrological interactions with the rock and soil beneath the ring laser monument. The large seasonal temperature effect on the G ring laser as well as the substantial local tilt signals and the rather high ambient noise level of our near soil surface structures give reasonable hope of much better performances of a ring laser installation in a deep underground laboratory such as the Gran Sasso laboratory of INFN (Istituto Nazionale di Fisica Nucleare). For the detection of fundamental physics signals one has to remove all known perturbation signals of the Earth from the ring laser time-series. Furthermore we have applied 2 hours of averaging of the data in order to reduce the effect from short period perturbations. Figure 4 shows an example. In order to reduce the local orientation uncertainties, which remain after local tilts measured with the high resolution tiltmeters have been removed, averaging as indicated above was applied to a series of 30 days of data collection, including the period shown in fig. 3. It can be expected that a similar data set from the GranSasso laboratory would become substantially smoother, since most of the perturbations, caused by ambient atmosphere - topsoil interaction still contained in the data of fig. 4 would no longer exist in the deep underground facility. Changing hydro-logic fluxes presumably causing small local rotation, temperature variations, atmospheric pressure and wind loading are among the sources for the systematic signatures in the residual data. Despite the fact that large ring lasers are very stable platforms and with the provision of tight feedback systems to stabilize the scale factor (cold cavity, as well as the active cavity), currently ring laser gyroscope are not able to determine the DC part of the Earth rotation rate with a sensitivity compatible with the requirements for detection of the Lense-Thirring effect. While the contribution of the varying Earth rotation itself presumably can be removed with sufficient accuracy from the C04 series of VLBI measurements, there remains the problem of determining the actual null-shift offsets from the laser functions in the ring laser gyroscope. Since the gravito-magnetic effect is small and constant, a good discrimination against laser biases, such as for example ‘Fresnel drag’ inside the laser cavity must be achieved. Therefore it will be advantageous to add one or several ring laser cavities in addition to the triad structure for sufficient redundancy. We also intend to operate at least the G ring laser structure in parallel to the here proposed structure in order discriminate local perturbation signals from regional and global ones. A second large ring laser located at the Cashmere facility in Christchurch, New Zealand will be used in the data analysis process, provided it can be run with sufficient resolution and stability. We outline our first experimental design. Primarily this represents an attempt to obtain the required accuracy in the angles by using pairs of gyroscopes (twins), located astride the relevant positions and exploiting the possibility to reduce (by subtraction) the big slowly changing contributions while enhancing the weak terms whose sign changes on the two sides of the orientation which provides zero Sagnac. The experimental set-up is composed of a central rigid heavy body, called a monument, to whom all the gyrolasers are rigidly attached, fig. 5 shows the set up described here. The monument itself plays an important role in this experiment. In order to provide a measurement base, we propose to use a massive block of concrete as a stable central reference. Around this concrete foundation, we ...
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Citations
... In this framework, the project GINGER (Gyroscopes IN GEneral Relativity) of the Istituto Italiano di Fisica Nucleare (INFN) was developed in 2010. 2,3 The goal of the project is to measure the Lense-Thirring and De Sitter effects using an on Earth device via a very precise and accurate measurement of the Earth rotation rate. Binding rigidly a RLG to the ground it is possible to exploit the Sagnac effect to measure the Earth rotation rate. ...
... The application of traditional gyroscopes such as mechanical rotor gyroscopes [1,2], laser gyroscopes [3], fiber optic gyroscopes [4], etc., has been severely restricted due to their large size, high cost and unsuitability for mass production. Benefiting from the small size, low cost, low power consumption and batch fabrication, MEMS gyroscopes have been widely used in the fields of automotive safety, mobile robots, consumer electronics, aerospace navigation, military weapons, etc., over the past few decades [5][6][7][8][9]. ...
This paper presents the design and optimization of a novel MEMS tuning fork gyroscope microstructure. In order to improve the mechanical sensitivity of the gyroscope, much research has been carried out in areas such as mode matching, improving the quality factor, etc. This paper focuses on the analysis of mode shape, and effectively optimizes the decoupling structure and size of the gyroscope. In terms of structural design, the vibration performance of the proposed structure was compared with other typical structures. It was found that slotting in the middle of the base improved the transmission efficiency of Coriolis vibration, and opening arc slots between the tines reduced the working modal order and frequency. In terms of size optimization, the Taguchi method was used to optimize the relevant feature sizes of the gyroscope. Compared with the initial structure, the transmission efficiency of Coriolis vibration of the optimized gyroscope was improved by about 18%, and the working modal frequency was reduced by about 2.7 kHz. Improvement of these two indicators will further improve the mechanical sensitivity of the gyroscope.
... To estimate the frequency, the second order autoregressive technique (AR2) employ two parameters such as a1 and a2 as given in equation (1) below: (1) Where The frequency is then calculated from the equation (2); (2) Frequency estimation can be done using MATLAB or LABVIEW whereby the values obtained are plotted on a graph to observe frequency variations and eventually its' efficiency. ...
... As mentioned before, when comparing the algorithms, Autoregressive is the reference because the aim of the comparison is to find out the algorithm that will surpass the performance of AR (2). ...
... The outputs from AR (2), Quinn as well as Phase technique produce the same output that depicts the rotation of the Earth. The remaining two techniques i.e., Pisarenko and Hilbert (Fig. 4 (d & e)) still outputs different characteristic which does not depict the rotation of the Earth; thus, they are not comparable to AR (2). ...
Autoregressive (AR2) technique has always been used to estimate frequency of the output signal from Large ring laser. However, the acquisition rate is not at near real time which is the requirement and noise level still challenge the process resulting to errors in the final estimation. A research was done to compare the Autoregressive (AR2) with the counterparts such as Pisarenko, Quinn, Hilbert and Phase looking for a better technique that will estimate the frequency at near real time to minimize errors. Secondary data from G and C – II ring laser were used during the comparison between the techniques and Autoregressive (AR2). Results shows that, the output characteristics from the counterpart does not depict the oscillations of the Earth rotation as expected contrast to that of Autoregressive (AR2) which does. Moreover, there were much deviation from the expected true value for the techniques contrast to that of AR2 which is very minimum. On the other hand, when the C – II data were used, it was observed that both techniques resemble on their output characteristics though AR2 was still better in the acquisition rate expect for Hilbert transform which does not resemble with others. Following the scope of this paper, Autoregressive (AR2) technique still emerge as a favorite frequency estimation technique contrast to the four counterparts due to its robustness, high acquisition rate as well as low noise level.
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The investigation of non-reciprocal behavior of optical beams in a rotating reference frame was the main motivation of the historic tabletop experiment of George Sagnac. His ground-breaking experiment was extended to a very large installation more than a decade later, which was sensitive enough to allow Michelson, Pearson and Gale to resolve the rotation rate of the Earth by an optical interferometer. With the advent of lasers in the early sixties of the last century, rotating laser cavities with a ring structure demonstrated superior performance and very soon matured to a point where mechanical gyroscopes were quickly superseded by laser gyroscopes in aircraft navigation. When vastly upscaled ring lasers were taken back to the laboratory at the end of the 20th century, the goal of applying the Sagnac effect to geodesy for the monitoring of tiny variations of Earth's rotation was the main motivation. The large-ring laser G, which is the most stable instrument out of a series of instruments built by the New Zealand–German collaboration, routinely resolves the rotation rate of the Earth to better than eight orders of magnitude. Since G is directly referenced to the Earth rotation axis, the effect of diurnal polar motion, the Chandler and the Annual wobbles as well as tilts from the solid Earth tides can be found in the interferogram obtained from the ring laser. G has also demonstrated high sensitivity to rotations associated with seismic events. The toroidal eigenmodes of the Earth when they are excited by large earthquakes have been resolved. A surprisingly large amplitude has been measured for Love wave signals contained in the microseismic background signal. This paper summarizes the recent development of highly sensitive large Sagnac gyroscopes, and presents unique results from the measurements of rotations of the earth.
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... Furthermore, no spinning mechanical parts are required, so these sensors can be manufactured in a very robust way and with a very high rejection of linear cinematic and gravitational accelerations from the rotational signal. Very large perimeter ring laser gyroscopes have found application in Geodesy, and General Relativity tests seem feasible in the near future (Di Virgilio et al. 2010a;Bosi et al. 2011). In the last years "G" ), a monolithic structure of zerodur (a glass-ceramic with ultra-low thermal expansion coefficient) supporting a squared cavity 4 m in side, operating by the Geodetic Observatory of Wettzel (Germany), was able to detect very small rotation signals like the twice-daily variations of the earth rotation axis due to solid earth tides (Schreiber et al. 2003) and the nearly diurnal retrograde polar motion of the instantaneous rotation pole caused by the lunisolar torques (Schreiber et al. 2004). ...
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... provides essential informations on rotational seismology [2], while its long term monitoring of the earth rotation rate makes it possible the direct observation of geodetic effects like the solid earth tides [3] and the diurnal polar motion [4]. The present sensitivity level is not too far from what is required for ground based General Relativity tests, which seem achievable in the near future by improved devices [5,6,7]. In this paper we present the experimental results concerning the use of a meter size gyrolaser as very sensitive tilt sensor. ...
We present a fully active-controlled He-Ne ring laser gyroscope, operating in
square cavity 1.35 m in side. The apparatus is designed to provide a very low
mechanical and thermal drift of the ring cavity geometry and is conceived to be
operative in two different orientations of the laser plane, in order to detect
rotations around the vertical or the horizontal direction. Since June 2010 the
system is active inside the Virgo interferometer central area with the aim of
performing high sensitivity measurements of environmental rotational noise. So
far, continuous not attempted operation of the gyroscope has been longer than
30 days. The main characteristics of the laser, the active remote-controlled
stabilization systems and the data acquisition techniques are presented. An
off-line data processing, supported by a simple model of the sensor, is shown
to improve the effective long term stability. A rotational sensitivity at the
level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the
required specification for the improvement of the Virgo suspension control
system, is demonstrated for the configuration where the laser plane is
horizontal.
We outline the scientific objectives, the experimental layout, and the collaborations envisaged for the GINGER (Gyroscopes in general relativity) project. The GINGER project brings together different scientific disciplines aiming at building an array of ring laser gyroscopes (RLGs), exploiting the Sagnac effect, to
measure continuously, with sensitivity better than pico-rad/s, large bandwidth (ca. 1 kHz), and high dynamic range, the absolute angular rotation rate of Earth. We address the feasibility of the apparatus with respect to the ambitious specifications above, as well as prove how such an apparatus, which will be able to detect strong
earthquakes, very weak geodetic signals, as well as general relativity effects like Lense–Thirring and de Sitter, will help scientific advancements in theoretical physics, geophysics, and geodesy, among other scientific fields.
