用快速傅氏变换作次声信号的动态谱分析

本文提出了应用小型数字计算机和快速傅氏变换作次声信号动态频谱的分析方法,实验证明这种方法行之有效,且容易实施,从而克服了模拟分析器难以克服的困难。本文介绍数字化频谱分析的一般原理,着重讨论记录在纸上的次声信号的采样和分析方面的有关问题,给出了用FORTRAN语言编写的动态谱分析计算程序和绘图程序,和一个实际例子的分析结果。     

Some effects of infrasound on task performance

Some effects of moderate levels of infrasound on the performance of a complex task have been investigated using two experimental designs. A comparison between these effects and those due to alcohol, audio frequency noise, and combinations of infrasound-alcohol and alcohol-audio frequency noise is also presented. The complex task adopted for these experiments consisted of (a) a centrally located high priority pointer following task which had to be performed continuously and (b) the response to the onset of any one of four lights two of which were situated in front of the subject and two on his periphery of vision. The task was performed over a period of 36 minutes. Our results indicate that although performance in the infrasound condition does not suffer significant decrements in either the primary task or the central and peripheral components of the secondary task, the effects through time, both within the infrasound condition and in relation to the control, produce changes which are of a different nature to those of audible noise. In audible noise performance is maintained through time, whereas with infrasound and alcohol it appears to be degraded.     

Some effects of infrasonic noise in transportation

Sound pressure level measurements in cars travelling at motorway speeds have shown that in many cases the overall level is very high in relation to the dB(A) and octave band levels, suggesting that much of the sound energy is in the low frequency and infrasonic regions. These levels have been measured down to the octave centred on 2 Hz. Experiments to investigate the effects of infrasound on balance and psychological awareness are described. The results show that levels of infrasound measured in moving vehicles can produce symptoms of balance disturbance, including vertical nystagmus, in normal observers, and also have profound effects on psychological awareness of normal human observers. Possible mechanisms for these effects are discussed.     

火箭发射的次声信号分析

在距离发射点20 km和230 km的两个阵列上,记录了我国一次火箭发射产生的次声波.从信号中识别出点火与声爆事件,观察到火箭在飞行中产生持续的次声波,以及声爆前后明显能量特征上的变化,观测到完整的火箭发射和飞行过程中系列次声波.为了验证采集信号中包含声爆事件,使用Fisher检测估计方位角和视速度,计算结果与火箭飞行...     

Uncertainties associated with parameter estimation in atmospheric infrasound arrays

This study describes a method for determining the statistical confidence in estimates of direction-of-arrival and trace velocity stemming from signals present in atmospheric infrasound data. It is assumed that the signal source is far enough removed from the infrasound sensor array that a plane-wave approximation holds, and that multipath and multiple source effects are not present. Propagation path and medium inhomogeneities are assumed not to be known at the time of signal detection, but the ensemble of time delays of signal arrivals between array sensor pairs is estimable and corrupted by uncorrelated Gaussian noise. The method results in a set of practical uncertainties that lend themselves to a geometric interpretation. Although quite general, this method is intended for use by analysts interpreting data from atmospheric acoustic arrays, or those interested in designing and deploying them. The method is applied to infrasound arrays typical of those deployed as a part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization.     

Noise in heavy goods vehicles

Data are given of noise spectra obtained in the cabs of new, and in-service, heavy goods vehicles having gross vehicle weights up to 40 tons. Comparisons are made between dB(A) and linear sound pressure levels under motorway conditions at 30, 40 and 50 mile/h.The emphasis has been on the collection of data, particularly in the infrasonic region, which lies in the octave bands between 2–20 Hz. The results confirm that high levels of infrasound exist in the cabs and these levels are, possibly, influenced by the ventilation of the cab and the road speed.The data obtained are discussed from the points of view of hearing hazard, impaired vigilance, and possible dangers arising from infrasound. It is concluded that in the noisier vehicles there is certainly a danger to hearing, and from available data on the effects of noise in the laboratory and in industry, there is probably some effect on vigilance. The extent of the possible hazard of infrasound is less well established and a need for further research is pointed out.     

Nonlinear synthesis of infrasound propagation through an inhomogeneous, absorbing atmosphere

An accurate and efficient method to predict infrasound amplitudes from large explosions in the atmosphere is required for diverse source types, including bolides, volcanic eruptions, and nuclear and chemical explosions. A finite-difference, time-domain approach is developed to solve a set of nonlinear fluid dynamic equations for total pressure, temperature, and density fields rather than acoustic perturbations. Three key features for the purpose of synthesizing nonlinear infrasound propagation in realistic media are that it includes gravitational terms, it allows for acoustic absorption, including molecular vibration losses at frequencies well below the molecular vibration frequencies, and the environmental models are constrained to have axial symmetry, allowing a three-dimensional simulation to be reduced to two dimensions. Numerical experiments are performed to assess the algorithm's accuracy and the effect of source amplitudes and atmospheric variability on infrasound waveforms and shock formation. Results show that infrasound waveforms steepen and their associated spectra are shifted to higher frequencies for nonlinear sources, leading to enhanced infrasound attenuation. Results also indicate that nonlinear infrasound amplitudes depend strongly on atmospheric temperature and pressure variations. The solution for total field variables and insertion of gravitational terms also allows for the computation of other disturbances generated by explosions, including gravity waves.     

Parametric acoustic antenna in the atmosphere

We consider the principles of development of a parametric antenna in the atmosphere. It is shown that to excite an infrasound at a frequency lower than 1 Hz in the atmosphere, one can use an acoustic system emitting simultaneously two waves whose frequencies differ by the infrasound frequency. In the pump-wave frequency range 20–500 Hz, the main contribution to infrasound emission is given by the region located at altitudes from 30 to 75 km, in which the oscillatory velocity in the pump wave is maximum. We propose an algorithm for calculation of the infrasound amplitude in the E and F layers of the ionosphere. Realization of a parametric antenna in the atmosphere makes it possible to broaden the capabilities of experiments based on the modification of the ionosphere by an infrasound. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 570–576, July 2006.     

The effects of low frequency noise on people—A review

During the fast few years, the existence of high levels of man-made low frequency noise (0–100 Hz), and in particular infrasonic noise, has been reported in many environments. An effort has been made over the last decade to discover whether such high levels of low frequency noise are significant. A review of the effects of low frequency noise indicates that the effects are similar to those of higher frequency noise, that noise in the 20–100 Hz range is much more significant than infrasound at similar sound pressure levels and that the possible danger due to infrasound has been much over-rated.     

Collective bubble oscillations as a component of surf infrasound

Plunging surf is a known generator of infrasound, though the mechanisms have not been clearly identified. A model based on collective bubble oscillations created by demise of the initially entrained air pocket is examined. Computed spectra are compared to infrasound data from the island of Kauai during periods of medium, large, and extreme surf. Model results suggest that bubble oscillations generated by plunging waves are plausible generators of infrasound, and that dynamic bubble plume evolution on a temporal scale comparable to the breaking wave period may contribute to the broad spectral lobe of dominant infrasonic energy observed in measured data. Application of an inverse model has potential to characterize breaking wave size distributions, energy, and temporal changes in seafloor morphology based on remotely sensed infrasound.     

基于一维卷积神经网络的化爆和地震次声分类

次声事件的分类识别方法应用广泛,传统分类方法在很多方面进行了尝试,但由于次声信号具备非线性的特点,致使分类难度较大,分类精度不高,这对次声事件的分类工作提出了挑战.针对次声事件中的化学爆炸与天然地震信号分类问题,文章构建了一种改进的深度卷积神经网络分类模型用于实现两类次声信号的分类.论文采用"全面禁止核试验条约组织"官...     

Low frequency and infrasonic noise in transportation

Recently, there has been much interest in infrasound and the possible effects it may have on people. Many industrial, office and home environments have been surveyed and some high levels of infrasound have been found. However, there has been very little spectral data reported at infrasonic frequencies for noise inside various modes of transportation, except for cars and trucks. This paper describes the results of an experimental programme in which infrasonic levels were established inside aircraft, ships, trains and road vehicles.     

The experimental research on response characteristics of coal samples under the uniaxial loading process

In order to study the response characteristics of infrasound in coal samples under the uniaxial loading process, coal samples were collected from GengCun mine. Coal rock stress loading device, acoustic emission tested system and infrasound tested system were used to test the infrasonic signal and acoustic emission signal under uniaxial loading process. The tested results were analyzed by the methods of wavelet filter, threshold denoise, time–frequency analysis and so on. The results showed that in the loading process, the change of the infrasonic wave displayed the characteristics of stage, and it could be divided into three stages: initial stage with a certain amount infrasound events, middle stage with few infrasound events, and late stage gradual decrease. It had a good consistency with changing characteristics of acoustic emission. At the same time, the frequency of infrasound was very low. It can propagate over a very long distance with little attenuation, and the characteristics of the infrasound before the destruction of the coal samples were obvious. A method of using the infrasound characteristics to predict the destruction of coal samples was proposed. This is of great significance to guide the prediction of geological hazards in coal mines.     

Topographic effects on infrasound propagation

Infrasound data were collected using portable arrays in a region of variable terrain elevation to quantify the effects of topography on observed signal amplitude and waveform features at distances less than 25 km from partially contained explosive sources during the Frozen Rock Experiment (FRE) in 2006. Observed infrasound signals varied in amplitude and waveform complexity, indicating propagation effects that are due in part to repeated local maxima and minima in the topography on the scale of the dominant wavelengths of the observed data. Numerical simulations using an empirically derived pressure source function combining published FRE accelerometer data and historical data from Project ESSEX, a time-domain parabolic equation model that accounted for local terrain elevation through terrain-masking, and local meteorological atmospheric profiles were able to explain some but not all of the observed signal features. Specifically, the simulations matched the timing of the observed infrasound signals but underestimated the waveform amplitude observed behind terrain features, suggesting complex scattering and absorption of energy associated with variable topography influences infrasonic energy more than previously observed.     

Tele-infrasonic studies of hard-rock mining explosions

The Lac-du-Bonnet infrasound station, IS-10, and the Minnesota iron mines 390 km to the southeast are ideally located to assess the accuracy of atmospheric profiles needed for infrasound modeling. Infrasonic data from 2003 associated with explosions at the iron mine were analyzed for effects of explosion size and atmospheric conditions on observations with well-constrained ground truth. Noise was the determining factor for observation; high noise conditions sometimes prevented unequivocal identification of infrasound arrivals. Observed arrivals had frequencies of 0.5 to 5 Hz, with a dominant frequency of 2 Hz, and generally had durations on the order of 10 s or less. There was no correlation between explosive amount and observability. Tele-infrasonic propagation distances (greater than 250 km) produce thermospheric ray paths. Modeling is based upon MSIS/HWM (Mass Spectrometer Incoherent Scatter/Horizontal Wind Model) and NRL-G2S (Naval Research Laboratory Ground to Space) datasets. The NRL-G2S dataset provided more accurate travel time predictions that the MSIS/HWM dataset. PE modeling for the NRL-G2S dataset indicates energy loss at higher frequencies (around 4 Hz). Additionally, applying the Sutherland/Bass model through the NRL-G2S realization of the atmosphere in InfraMAP results in predicted amplitudes too small to be observed.     

基于薄膜动圈式的次声波监测装置设计

基于薄膜动圈式声-电转换原理,利用次声波产生的空气微压波动带动薄膜上线圈受迫振动,引起线圈内磁通量的变化产生感应电动势,将声信号转换成电信号进行采集,设计便携式次声监测装置.在模拟简谐次声环境中的测量结果表明,该装置能够准确地测量出振动频率,并对其幅度进行监测.     

In situ calibration of atmospheric-infrasound sensors including the effects of wind-noise-reduction pipe systems

A worldwide network of more than 40 infrasound monitoring stations has been established as part of the effort to ensure compliance with the Comprehensive Nuclear Test Ban Treaty. Each station has four to eight individual infrasound elements in a kilometer-scale array for detection and bearing determination of acoustic events. The frequency range of interest covers a three-decade range-roughly from 0.01 to 10 Hz. A typical infrasound array element consists of a receiving transducer connected to a multiple-inlet pipe network to average spatially over the short-wavelength turbulence-associated "wind noise." Although the frequency response of the transducer itself may be known, the wind-noise reduction system modifies that response. In order to understand the system's impact on detection and identification of acoustical events, the overall frequency response must be determined. This paper describes a technique for measuring the absolute magnitude and phase of the frequency response of an infrasound element including the wind-noise-reduction piping by comparison calibration using ambient noise and a reference-microphone system. Measured coherence between the reference and the infrasound element and the consistency between the magnitude and the phase provide quality checks on the process.     

扬声器激励次声频校正器的设计和性能分析

为克服现有主流型活塞式次声校正器低频端漏气误差增大的缺点，该文提出基于扬声器激励、薄膜密封结构作为标准次声源，实现了一种新型次声校准装置。该装置采用成熟化技术方案和模块化设计，具有组装方便、体积小、重量轻和工作稳定等优点。目前在校准频率0.1～20 Hz范围内，合成标准不确定度在0.2 dB以内，扩展不确定度优于0.4 dB (k=2)。利用该装置分别对MB3a型和自研次声传感器进行了校准，前者的校准结果与产品技术参数一致，后者与中国计量科学研究院的校准结果相近(误差小于7.5%)，测试结果表明该装置可用于次声传感器的校准。值得注意的是，该校正器可能做到低端0.01 Hz或更低的频率的绝对校正，该文展望了扬声器激励次声校正器发展前景。     

Theoretical analysis of infrasound radiation from an oscillating bridge

As a typical example of the sound radiation caused by the oscillation of a large sized structure, the infrasound radiation from a highway bridge is theoretically analyzed by applying a lifting surface technique. The relation between the bridge oscillation and the corresponding infrasound radiation is made clear quantitatively. By using measured results of the bridge oscillation due to the passage of a vehicle, the infrasound radiated from the bridge is estimated analytically. The results are compared with the measurements, and good agreement is seen. Moreover, it is shown that the reflection of sound at the ground causes both the radiation impedance of the bridge and the radiation pattern of the sound pressure to vary considerably according to the height of the bridge from the ground. Hence the height of the bridge is an important factor which controls sound pressure level (SPL) near the ground, on which the noise is actually perceived.