Acceleration Noise Research Articles

The Influence of Temperature Disturbance on Space Inertial Sensors.

The TianQin program is an independently proposed space-borne detection initiative from China. The inertial sensor, as a crucial component, is susceptible to disturbances from temperature fluctuations, the impact of which on acceleration measurements remains elusive. Therefore, a comprehensive analysis on the influence of temperature disturbance is necessary to avoid errors in acceleration measurement. In this study, we proposed a complete scheme for calculating the level of acceleration noise. Based on the traditional temperature control scheme of using a heat pipe, we developed a systematic heat transfer simulation model to obtain the temperature signals. These signals can then be converted into the frequency domain and used to calculate the acceleration noise level within the target bandwidth. Our results indicate that, with a temperature control of 0.13 K/Hz1/2@1 mHz, the largest contributions to acceleration noise come from the outgassing effect, radiometer effect, and radiative pressure effect, in descending order. The total noise peak is 3.6×10-12 m/(s2⋅Hz1/2) at 1 mHz, which is more than three orders of magnitude higher than the TianQin target of 10-15 m/(s2⋅Hz1/2). This study provides new avenues for evaluating measurement errors and solutions for the TianQin program.

Optimizing electrostatic acceleration noise by precisely adjusting the differential potential between the electrodes and test mass for space inertial sensors

Optimizing electrostatic acceleration noise by precisely adjusting the differential potential between the electrodes and test mass for space inertial sensors

Estimate of in-band eddy current effect in space gravitational wave detection

Abstract In space detection of gravitational waves (GWs), the presence of a low-frequency varying magnetic field will generate eddy currents in the test mass, resulting in a varying magnetic moment. This magnetic moment will couple with a constant magnetic field gradient, producing residual acceleration within the frequency band of GW detection, causing the test mass to deviate from the free-falling mode. However, this effect has not yet been studied clearly in the noise budget for TianQin and LISA Pathfinder since the constant DC magnetic susceptibility was applied to quantify the varying magnetic moment. This paper utilizes the parameter of alternating current (AC) magnetic susceptibility to define this process, and further analyzes and evaluates the effect. In a general magnetic field environment, the contribution of this effect to TianQin acceleration noise reaches 20\% from 0.1 mHz to 3 mHz. The contribution to LISA noise is less than 10\% from $10^{-4}$ to 0.1 Hz, and less than 10\% below $10^{-4}$ Hz. This effect does not have a potential limit on LISA low-frequency science down to 20 $\mu$Hz [Phys. Rev. Lett. 120, 061101 (2018)].

Exploring realistic vehicle acceleration sounds through discomfort index analysis

Contemporary Japanese society's heavy reliance on automobiles is shifting from transportation to leisure, amidst rising environmental concerns over emissions. This has led to a pivot towards eco-friendly options, notably clean diesel vehicles (DVs) and electric vehicles (EVs), due to Europe's stringent regulations. DVs aim to lower harmful emissions, while EVs are favored for their minimal emissions and silent operation. However, EVs' lack of audible acceleration noise poses safety risks, as drivers may struggle to perceive speed changes. The study investigated how deviations in expected engine sounds impact perceived sound quality and vehicle performance assessment, focusing on DV and EV acceleration sounds. It explored the integration of certain sensations (rumbling, booming, humming) into EV sounds to enhance realism, assessing comfort levels among drivers with varying experience.

Decoupling method of self-gravity compensation based on spherical multipole expansion for space gravitational wave detectors

In space gravitational wave detection missions, the gravity and its gradients produced by the spacecraft on the two Test Masses (TMs) are commonly referred to as the Self-Gravity(SG). It is an important source of TM disturbances in gravitational wave detection and other drag-free space missions and will affect the TM acceleration noise in many ways. The SG can be reduced by adding Balance Masses (BMs). But for typical space gravitational wave detectors, in which the sensitive axes of the two TMs are at an angle of 60°, the couplings of different SG components of two TMs make the gravity compensation process complicated in practice, which is normally an iterative process. This paper analyses the correspondence between the SG components of the two TMs and the spherical harmonics of different orders, and proposes a compensation method based on spherical multipole expansion. This method allows independent design of the BMs for most of the main SG components, without couplings and iterations. To verify this method, a self-gravity compensation simulation is carried out by using a demonstrating spacecraft structural model for TianQin gravitational wave detection mission. Three sets of BMs are designed on the outer surface of the inertial sensor vacuum chamber, to compensate for the two linear accelerations and one linear gradient that exceed the requirements. The results show that the SG components after compensation are two orders of magnitude lower than the initial level, and all the components meet the preliminary requirements of TianQin mission. This study could provide reference for the engineering design and development of the spacecraft and inertial sensor payload for space gravitational wave detection missions.

Charging and Discharging Modeling of Inertial Sensors Based on Ultraviolet Charge Management

Inertial sensors act as inertial references in space gravitational wave detection missions, necessitating that their internal test mass (TM) maintains minimal residual acceleration noise. High-energy particles and cosmic rays in space, along with ion pumps in ground-based torsion pendulum experiments, can cause charge accumulation on the TM surface, leading to increased residual acceleration noise. Consequently, a charge management system was introduced to control the TM’s charge. The complex light path propagation within the electrode housing (EH) makes the TM’s charging and discharging process difficult to theoretically calculate and fully simulate. To address this issue, we propose a simulation method for charging and discharging inertial sensors within ultraviolet (UV) charge management systems. This method innovatively considers the impact of photoelectron emission angle and the TM’s position offset from symmetry on performance. The method also simulates charging and discharging rates over time under conditions of symmetry and preliminarily examines factors affecting the TM’s equilibrium potential. Simulation results indicate that this method effectively models the charge management system’s operation, providing a valuable reference for system design.

Magnetic field dynamics and noise analysis for space-based GW detector in far-earth orbits: A hybrid modeling approach

TianQin (TQ) mission, the sole proposed gravitational wave detection project in geocentric orbit at an altitude of approximately 105 km, traverses diverse geomagnetic regions. This paper employs a hybrid model to simulate the ambient magnetic field along the TQ orbit, investigating magnetically-induced acceleration noise under varying satellite-sun angles (SSA) and solar activity levels. The highest noise level, approximately 10−16ms−2Hz−1/2, occurs during transregional periods between the magnetosheath (MSH) and magnetotail (MTL). Noise within the MSH region is an order of magnitude lower than the former, with the MTL region exhibiting the lowest levels, although geomagnetic storms can equalize noise in both regions. Statistical analysis indicates that noise in the MTL region correlates with SSA and solar wind dynamic pressure, displaying a spectral characteristic of f−1.03±0.075, while the MSH region shows a Kolmogorov turbulence spectrum near the flank and f−0.5 at the subsolar region.

Removing spikes in TianQin-1 inertial sensor data using machine learning method

Abstract The spikes in the inertial sensor data have been found to impact on the retrieval of the non-gravitational signals and the evaluation of the inertial sensor performance. Removing the spikes in the inertial sensor is critical for studies of gravitational reference sensors in space-based gravitational wave detection missions and accelerometers in gravity satellite missions. Thanks to a long period of inertial sensor data without thruster spikes, we can conduct machine learning based on this data to remove spikes. In this paper, a machine learning model called bi-directional long short-term memory (Bi-LSTM) neural network was built based on the inertial sensor data of TianQin-1 (TQ-1) mission. We use the machine learning method to remove the spikes in the inertial sensor data. After removing the spikes in the inertial sensor data, acceleration noise is suppressed form 2.0×10-7ms-2Hz-1/2 to the 2.8×10-10ms-2 Hz-1/2 at 0.1 Hz, which is far better than the existing methods, including the linear interpolation, data substitution and mean value of adjacent data.

Integration of High-Rate GNSS and Strong Motion Record Based on Sage–Husa Kalman Filter with Adaptive Estimation of Strong Motion Acceleration Noise Uncertainty

A strong motion seismometer is a kind of inertial sensor, and it can record middle- to high-frequency ground accelerations. The double-integration from acceleration to displacement amplifies errors caused by tilt, rotation, hysteresis, non-linear instrument response, and noise. This leads to long-period, non-physical baseline drifts in the integrated displacements. GNSS enables the direct observation of the ground displacements, with an accuracy of several millimeters to centimeters and a sample rate of 1 Hz to 50 Hz. Combining GNSS and a strong motion seismometer, one can obtain an accurate displacement series. Typically, a Kalman filter is adopted to integrate GNSS displacements and strong motion accelerations, using the empirical values of noise uncertainty. Considering that there are significantly different errors introduced by the above-mentioned tilt, rotation, hysteresis, and non-linear instrument response at different stations or at different times at the same station, it is inappropriate to employ a fixed noise uncertainty for strong motion accelerations. In this paper, we present a Sage–Husa Kalman filter, where the noise uncertainty of strong motion acceleration is adaptively estimated, to integrate GNSS and strong motion acceleration for obtaining the displacement series. The performance of the proposed method was validated by a shake table simulation experiment and the GNSS/strong motion co-located stations collected during the 2023 Mw 7.8 and Mw 7.6 earthquake doublet in southeast Turkey. The experimental results show that the proposed method enhances the adaptability to the variation of strong motion accelerometer noise level and improves the precision of integrated displacement series. The displacement derived from the proposed method was up to 28% more accurate than those from the Kalman filter in the shake table test, and the correlation coefficient with respect to the references arrived at 0.99. The application to the earthquake event shows that the proposed method can capture seismic waveforms at a promotion of 46% and 23% in the horizontal and vertical directions, respectively, compared with the results of the Kalman filter.

The evaluation for plasma noise in arbitrary time-delay interferometry combinations

The laser interferometer space antenna (LISA) uses laser interferometry to measure gravitational wave-induced distance changes between freely falling test masses on separate spacecraft. In practice, the space-borne gravitational wave detector operates in a plasma medium, and subsequently, the variations in electron density affect the refractive index and add displacement noise to measurements. Geometric time-delay interferometry (TDI) is the TDI combinations searched by geometric method, which is employed to mitigate overwhelming laser phase noise. This study explores all forty-five second-generation geometric TDI combinations up to sixteen links, analyzing plasma noise effects via power spectral density and cross-spectral density calculations for different optical links. Our findings reveal that plasma noise can exceed the noise floor, which comprises optical metrology system and test mass acceleration noise, in certain low-frequency regions due to different noise transfer behaviors. Further, we establish electron density requirements for various TDI combinations, showing that densities below 100cm−3/Hz @ 10mHz satisfy LISA’s criteria across all forty-five combinations. This allows for optimized TDI selection based on specific plasma densities.

Time delay interferometry combination with zero-response

In space-based gravitational wave detection, gravitational wave signals are detected by measuring the Doppler frequency shift of laser exchange between three satellites. Although the laser is pre-stabilized, the laser phase noise is significantly higher than the gravitational wave signal, approximately 7–8 orders of magnitude higher. To reduce the otherwise-overwhelming laser phase noise, the time delay interferometry (TDI) technique is employed by properly time-shifting and linearly combining raw data. Different TDI combinations have various abilities in suppressing laser phase noise, and the response function of gravitational wave signal as well as the power spectral density of noise floor (including test mass acceleration noise and optical path noise) are also different. In this work, we present a unique class of TDI combinations, denoted as [ZX]116,[ZX]216,[ZX]316,[ZX]416, and [ZX]516, which exhibit a distinct geometric space–time diagrams composed of Michelson interferometers as the fundamental constituents. Specifically, when the detector arm lengths are assumed to be equal, these combinations yield response functions and noise power spectral densities of zero. To evaluate the detection performance of these combinations, we investigate their response functions and noise power spectral densities when the detector arm lengths are unequal, and furthermore, derive the analytical expressions for their sensitivity functions. Through our analysis, we have discovered some intriguing results. When the detector arm lengths are unequal, both the response functions and noise spectral densities of these combinations are correlated with the difference in arm lengths L3−L2. However, the sensitivity functions of these TDI combinations remain unaffected by the specific values of the arm length difference, and are consistent with the sensitivity functions of widely-used TDI combinations. For instance, the sensitivity function of [ZX]116 combination is the same as that of the Michelson combination, while the sensitivity functions of [ZX]216 and [ZX]416 combinations match with that of the Sagnac combination. Furthermore, the [ZX]316 and [ZX]516 combinations share the same sensitivity function as the fully symmetric Sagnac combination, enabling the identification of instrument noise and stochastic gravitational wave backgrounds. The discovery of this class of combinations provides support for the diversity of data processing.

A Multi-Agent Driving-Simulation Approach for Characterizing Hazardous Vehicle Interactions between Autonomous Vehicles and Manual Vehicles

The advent of autonomous vehicles (AVs) in the traffic stream is expected to innovatively prevent crashes resulting from human errors in manually driven vehicles (MVs). However, substantial safety benefits due to AVs are not achievable quickly because the mixed-traffic conditions in which AVs and MVs coexist in the current road infrastructure will continue for a considerably long period of time. The purpose of this study is to develop a methodology to evaluate the driving safety of mixed car-following situations between AVs and MVs on freeways based on a multi-agent driving-simulation (MADS) technique. Evaluation results were used to answer the question ‘What road condition would make the mixed car-following situations hazardous?’ Three safety indicators, including the acceleration noise, the standard deviation of the lane position, and the headway, were used to characterize the maneuvering behavior of the mixed car-following pairs in terms of driving safety. It was found that the inter-vehicle safety of mixed pairs was poor when they drove on a road section with a horizontal curve length of 1000 m and downhill slope of 1% or 3%. A set of road sections were identified, using the proposed evaluation method, as hazardous conditions for mixed car-following pairs consisting of AVs and MVs. The outcome of this study will be useful for supporting the establishment of safer road environments and developing novel V2X-based trafficsafetyinformation content that enables the enhancement of mixed-traffic safety.

High-Precision Inertial Sensor Charge Ground Measurement Method Based on Phase-Sensitive Demodulation

Inertial sensors are the key payloads in space gravitational wave detection missions, and they need to ensure that the test mass (TM), which serves as the inertial reference, freely floats in the spacecraft without contact, so that the TM is not disturbed by the satellite platform and the cosmic environment. Space gravitational wave detection missions require that the residual acceleration of the TM should be less than 3×10−15ms−2Hz−1/2. However, the TM with charges will interact with surrounding conductors and magnetic fields, introducing acceleration noise such as electrostatic force and Lorentz force. Therefore, it is necessary to carry out charge management on the TM, in which the high-precision measurement of charge is crucial. Space gravitational wave detection missions require a residual charge measurement accuracy of 3×10−13C for the TM. In this paper, we design a high-precision inertial sensor charge measurement method based on phase-sensitive demodulation (PSD). By establishing a torsion pendulum rotation model based on the force modulation method, the characteristics of the TM torsion angle signal are analyzed. The PSD is used to extract the amplitude of the specific frequency signal component containing the charge information, and then to calculate the value of the accumulated charges. The method is compared with the Butterworth band-pass filtering method, and the simulation results show that the method has a higher measurement accuracy, shorter settling time, and stronger anti-interference ability, meeting the TM residual charge measurement accuracy index requirement.

Application of ultraviolet light sources in charge management systems for space gravitational wave detection

Gravitational waves are a kind of matter wave, which is caused by the violent motion and changes of matter and energy. Detecting gravitational waves allows people to observe the universe from a new perspective. In the process of gravitational wave detection, high-energy particles and cosmic rays in space can penetrate the exterior of the spacecraft and reach the surface of the inertial sensor's test mass (TM), continuously accumulating charges. Once the charge on the TM exceeds a certain threshold, the electrostatic forces between the TM and surrounding conductors generate significant acceleration noise, which will affect the measurement accuracy of the inertial sensors and, consequently, the success of the gravitational wave detection mission. Therefore, controlling the charge on the TM surface, known as charge management, is essential. The most commonly used charge management method is based on the photoelectric effect, using ultraviolet (UV) light to control the potential between the surface of the TM and the surrounding conductors. In previous charge management systems (CMSs), UV mercury lamps and UV light-emitting diodes (LEDs) were used as light sources, achieving varying levels of success. This paper mainly reviews the research progress of UV light sources in CMS for space gravitational wave detection. Mercury lamps, as the first-generation system light source, can fulfill the mission but have some drawbacks such as slow startup, high power consumption and significant electromagnetic interference. UV LEDs, because of their advantages in size and weight, have gradually become the current light source for CMS. In recent years, with the development of UV micro-LED technology, UV LEDs have achieved higher external quantum efficiency and lower power consumption, demonstrating their potential applications in CMS, and becoming a promising UV light source for future charge management systems.

IMPROVING THE EFFICIENCY OF PROCESS MANAGEMENT IN THE FIELD OF TRAFFIC SAFETY ACCORDING TO ADDITIONAL CRITERIA

Known methods of assessing the level of traffic safety on highway sections are considered. When developing or improving road safety assessment methods, it is necessary to establish, among other things, the influence of variable road factors on traffic safety and to give a quantitative and qualitative assessment of the degree of their change. Factors that can significantly affect forecasting accuracy have been identified. All methods of detecting dangerous areas that are currently available are offered, based on traffic accident statistics. At different times, the following methods were proposed: analysis of statistical data by the methods of probability theory; use of multivariate correlation analysis data; analysis of traffic speed charts (methods of safety factors and "acceleration noise"); analysis using coefficients of relative influence of individual elements of the road (method of accident rates); method of conflict situations. It is proposed to improve the existing method by introducing additional parameters, which were obtained as a result of the formalization of accident statistics at the places of concentration of traffic accidents. It is proposed to evaluate traffic safety conditions by the final sum of points (on a 100-point scale), which takes into account a number of road construction characteristics. In our opinion, in conditions where the assessment of road safety conditions is entrusted to the representatives of the highway owner, this method looks more effective, since the road owner does not always or does not fully possess reliable statistical information about road accidents in the area being evaluated. The proposed method of evaluating the level of traffic safety is an undoubted step forward on the path of simplification and clarification existing methods. In the future, work on the construction of a simulation model of the interaction of the driver and the road as a subsystem of the general system "driver-car-road-environment" looks promising, by relying on criteria that were previously neglected - technical means of traffic management. This will make it possible to calibrate the proposed method and transfer its action to the software environment. In this way, the research will receive a significant platform for the involvement of additional variables - taking into account the road category, time of day, informativeness of technical means, their deformability, etc.

Evaluating residual acceleration noise for the TianQin gravitational waves observatory with an empirical magnetic field model

Evaluating residual acceleration noise for the TianQin gravitational waves observatory with an empirical magnetic field model

Дослідження показників якості організації дорожнього руху в умовах міста методом GPS-треків

The choice of rational quality criteria for the organization of road traffic in cities is an urgent task for scientists in the field of road transport, as it directly affects the effectiveness of activities in the field of ensuring the safety and comfort of car traffic in urban conditions. Depending on the goals of the analysis, the complexity of the network, and technical capabilities, the quality of traffic management can be assessed by indicators of the economic efficiency of the transport process, the level of accidents, environmental safety, social attractiveness, etc. The modern level of development of geo-information technologies allows for constant monitoring of the vehicle's speed mode. To obtain characteristics of the quality of traffic organization, experimental studies were conducted on a section of the street-road network of the city of Kharkiv, which corresponds to a typical route of personal transport from a remote sleeping area to the central part of the city.
 As a result of data processing of the GPS track, a histogram of the distribution of instantaneous speed and graphs of the car’s movement in the coordinates “time-distance”, “time-speed”, "distance-speed” were built, which allow you to visually assess the mode of movement along the entire route and determine potential "bottlenecks". Such spatio-temporal characteristics as average technical speed, specific time in motion, specific idle time, as well as energy indicators of the quality of traffic management were also calculated: acceleration noise, speed gradient, energy gradient. After dividing the experimental route into separate kilometer sections, changes in the characteristics of the quality of traffic organization, as it approached the city center, were analyzed. On the first half of the route, when moving along the main street, the instability of the speed regime was observed due to stops and idling in the zone of regulated intersections. The presence of a trend towards a decrease in the average technical speed when approaching the city center is explained by an increase in the loading of VDM within the central business part of the city and, as a result, the appearance of additional traffic delays. As we approached the city center, the specific time in motion increased with a slight increase in the specific idle time, and an increase in the speed gradient was also observed with a slight decrease in the energy gradient.

Analysis of the calculation method and evaluation of the magnetic acceleration noise of space inertial sensor

Accurately calculating the magnetic acceleration noise is essential to designing the space inertial sensor and constructing its evaluation system. In view of the shortcomings of the magnetic acceleration noise calculation model, which considers the test mass (TM) as an ideal magnetic dipole rather than an entity, the Maxwell stress tensor method (MSTM) and virtual work principle method (VWPM), which consider the influence of the shape and size of the TM into account are adopted in this study. Through comparison, it is concluded that the non-uniformities of the internal magnetic field and magnetization intensity of the TM are the reasons for the calculation error of the model, and when the magnetic susceptibility is <1 × 10−2, the model can satisfy the requirement of the calculation accuracy. Finally, two specific signals of the near-interplanetary magnetic field and the magnetic field of a circuit board were measured in a magnetic shielding room (MSR), and the magnetic acceleration noises induced by the two magnetic environments were calculated. These can act as significant reference values for magnetic acceleration noise experiments in orbit and the layout of electronic devices in satellite engineering.

Magnetic field recovery technique based on distance weighting multipole expansion method

A space-borne gravitational wave detector requires the test mass (TM) to be in an ultra-low disturbance state. However, magnetic field fluctuations will disturb the TM and produce acceleration noise. To assess the influence of the magnetic field on the TM, it is necessary to monitor and reconstruct the magnetic field near the TM in real time. In this paper, a distance weighting multipole expansion (DWME) method was proposed, and its magnetic field reconstruction accuracy was analyzed. The results demonstrated that the proposed DWME method significantly improved the reconstruction precision compared to traditional methods. It reduced the average reconstruction error of the sensitive axial magnetic field from 1.2% to 0.8% and the maximum error from 16% to 8%. In the in-orbit situation, the DWME method also outperforms traditional methods.

High-Sensitivity Seismometer Development for Lunar Applications.

Lunar seismology is a critical area of research, providing insights into the Moon's internal structure, composition, and thermal history, as well as informing the design of safe and resilient habitats for future human settlements. This paper presents the development of a state-of-the-art, three-axis broadband seismometer with a low-frequency range of 0.001-1 Hz and a target sensitivity over one order of magnitude greater than previous Apollo-era instruments. The paper details the design, assembly, methodology, and test results. We compare the acceleration noise of our prototype and commercial seismometers across all three axes. Increasing the test mass and reducing its natural frequency may further improve performance. These advancements in seismometer technology hold promise for enhancing our understanding of the Moon's and other celestial bodies' internal structures and for informing the design of future landed missions to ocean worlds.