共查询到20条相似文献，搜索用时 234 毫秒
1.
海平面的海啸波会产生大气重力波进而引发电离层扰动.本文利用日本GPS总电子含量数据来探测2011年3月11日Tohoku海啸引发的电离层扰动.观测结果表明,在日本上空的电离层中存在两种重力波信号,分别由海平面的海啸波以及地震破裂过程产生.地震产生的电离层重力波分布在震中周围（包括海洋上空以及远离海洋的区域）,而海啸引发的电离层重力波主要分布在海洋上空.地震产生的电离层重力波具有不同的水平速度,包括约210 m·s-1以及170 m·s-1,其频率为1.5 mHz;而海啸引发的电离层重力波水平速度快于前者,约为280 m·s-1,其频率为1.0 mHz.此外,海啸引发电离层重力波与海平面上的海啸波有相似的水平速度、方向、运行时间、波形以及频率等传播特征.本文的研究将电离层中的海啸信号与地震信号区分开来,进一步确认电离层对海啸波的敏感性. 相似文献
2.
本文分析了电离层的变化和运动引起多普勒频移的物理机制,假定了一个包含多种因素的电离层模型。在此基础上得到电离层反射信号的多普勒频移公式以及穿过电离层的信号的多普勒频移公式。这些公式把多普勒频移与电离层及不均匀团块的电子密度变化、层和团块的运动速度以及地球磁场强度变化等参数直接联系起来。 相似文献
3.
With the use of data from topside sounding on board the Interkosmos-19 (IK-19) satellite, the region of permanent generation of large-scale irregularities in the daytime winter ionosphere of the Southern Hemisphere is differentiated. This region is characterized by low values of foF2 and hmF2 and occupies a rather large latitudinal band, from the equatorial anomaly ridge to ~70° S within the longitudinal range from 180° to 360°. Irregularities with a dimension of hundreds kilometers are regularly observed in the period from 0700–0800 to 1800–1900 LT, i.e., mainly in the daytime. In the IK-19 ionograms, they normally appear in the form of an extra trace with a critical frequency higher than that of the main trace reflected from the ionosphere with lower density. The electron density in the irregularity maximum sometimes exceeds the density of the background ionosphere by nearly a factor of 3. A model of the ionosphere with allowance for its irregular structure was created, and it was shown on the basis of trajectory calculations how the IK-19 ionograms related to these irregularities are formed. A possible mechanism of the generation of large-scale irregularities of the ionospheric plasma is discussed. 相似文献
4.
A method for estimating absorption value on the basis on one ionogram of a vertical sounding dynasonde was proposed. The main idea is that averaging the amplitudes of the signals reflected from the ionosphere is replaced over time by frequency averaging of the amplitude factor introduced by the authors. The amplitude factor was determined. The regularities of daily variations in the amplitude factor are discussed. 相似文献
5.
The results of observations of quasi-periodic variations of horizontal components of the geomagnetic field, the Doppler frequency shift of the radio waves reflected from the ionosphere, and observations of anomalous traces in ionograms during a catastrophe at the largest European ammunition depot on March 23, 2017, are presented. It is shown that the catastrophe was accompanied by oscillations of the geomagnetic field level (with periods from 5–6 to 13–14 min and an amplitude of 2–3 nT) and the ionospheric electron density (with periods from 14–16 to 50–60 min and a relative amplitude of ～1–10%). A mechanism for the transfer of disturbances from the catastrophe site to the ionosphere altitudes is proposed. A key role in this mechanism is played by the acoustic gravity waves generated by widespread explosions and large-scale fire events. 相似文献
6.
《Journal of Atmospheric and Solar》2000,62(15):1361-1376
A homing-in method is presented for determining ionospheric reflected or transionospheric paths between fixed transmitter and receiver locations in the presence of ionospheric gradients or ripples. Both initial elevation and azimuth are automatically adjusted to find the path that arrives exactly at the receiver. The method can be used for any 3D ionospheric model to find precise ray paths and phase and group delays for both magneto-ionic modes. The method takes full account of path location, geomagnetic field orientation and the bending of the ray path resulting from horizontal as well as vertical gradients of electron density. It can also find multiple paths e.g. low and high angle, 1- and 2-hops for both ordinary and extraordinary modes. Examples of its use are given for both terrestrial HF links and Earth to Satellite paths. For paths reflected from the ionosphere, the effect of gradients of both critical frequency and height of maximum electron density are determined and the comparative effect of gradients on high and low angle and 1- and 2-hops paths for both magneto-ionic modes investigated. Path variation with frequency for a fixed link is also studied and the bandwidth of the ionospheric background channel (dispersive bandwidth) and its reciprocal (the pulse rise time), important for wideband digital HF broadcasting or spread spectrum HF communications, is estimated for a range of frequencies, for high- and low-angle rays and 1- and 2-hop paths. For Earth–satellite paths, the effect of the ionosphere and horizontal ionospheric gradients is determined for a range of frequencies and elevation angles. It is shown that the method can also enable the determination of second-order errors in satellite navigation methods, such as GPS, due to ionospheric gradients and the effect of the geomagnetic field. 相似文献
7.
用于低渗砂岩油气开发的压裂需要地层的纵横波时差参数;压裂形成的人工裂缝或砂泥岩中的自然裂缝是油气流入井中的主要通道.声波测井是测量地层的纵横波时差、探测连通裂缝的有效方法.本文给出了新设计的偶极子组合声波测井仪器在低渗砂泥岩地层所测量的波形.新仪器利用声波在井内传播的固有频率设计探头,利用探头阻抗随频率的变化曲线设计匹配电路,有效地提高了声发射功率,在井下采用16位A/D转换器提高了原始波形的采样精度.测量的波形比通常的声波测井波形所含的地层信息丰富.单极子长源距声波测井波形中除了通常的纵、横波和Stoneley波外,还发现了起始于纵波首波的反射波以及随深度改变其到达时间的后续波.通过与其它测井曲线综合对比发现:其反射波与井眼扩径有关,使测量的声波时差加大;后续波在显示地层特征的同时,与横波混叠在一起,使横波时差的提取变得困难.另外,在偶极子所测量的低频波形中也发现了明显的反映地层连通裂缝的反射波,该反射波可以用于指示低渗砂岩地层中的连通裂缝. 相似文献
8.
Physical mechanisms of man-made influences on the magnetosphere 总被引：3，自引：0，他引：3
Since the discovery of the Luxembourg effect in the 1930s, it is clear that man-made activities can perturb the ionosphere and the magnetosphere. The anthropogenic effects are mainly due to different kinds of waves coming from the Earth's surface. Acoustic-gravity waves are generated by large explosions, spacecraft launches, or flight of supersonic planes. Electromagnetic waves are active in different frequency ranges. Power line harmonic radiation which is radiated in the ELF range by electrical power systems can be observed over industrial areas. At VLF and HF, the ground-based transmitters used for communications or radio-navigation heat the ionosphere and change the natural parameters. A large variety of phenomena is observed: wave-particle interaction, precipitation of radiation belt electrons, parametric coupling of EM whistler waves, triggered emissions, frequency shift, and whistler spectrum broadening. This paper will review the different physical mechanisms which are relevant to such perturbations. The possibility of direct chemical pollution in the ionosphere due to gas releases is also discussed. 相似文献
9.
利用全波解算法模拟哨声波束在甚低纬地区黎明前低电离层透射的三维能量分布，依据波场能量和偏振分布及其对波参量和电子浓度剖面的依赖特征，分析了哨声透射、反射及与大地－电离层波导耦合过程．结果表明，哨声模波存在于９０ｋｍ以上高度，吸收、反射、波束扩展及波模转换主要发生于电离层底部８０－９０ｋｍ区间；到达地面的透射能量密度衰减２０ｄＢ以上，透射衰减随频率变化不大，但随波入射角呈不对称变化；距透射区１５０ｋｍ以外区域的测向方位角有很大偏差；入射波能量的很少一部分（对５ｋＨｚ约为－２５ｄＢ）被反射并激发起哨声模波，反射波束能量集中于入射波束附近，并随频率下降而迅速增强．计算也表明，地面接收到的甚低纬哨声回波可能与使回波向极侧偏移的电离纬向梯度有关． 相似文献
10.
S. I. Musatenko A. V. Agapitov E. V. Kurochka A. S. Slipchenko V. V. Fomichev A. K. Markeev S. M. Kutuzov 《Geomagnetism and Aeronomy》2006,46(5):667-675
Results of the spectral measurements of ionospheric noise in the meter band are presented. The events lasting several milliseconds (the emission maximum of which drifts upward (in frequency), is reflected (stops), and drifts downward) have been distinguished. Moreover, multiple harmonics are observed. The frequency-time structure of such events have been considered from the viewpoint of registration of the electron beam synchrotron emission harmonics at ionospheric altitudes in the geomagnetic field. The model calculations of the frequency-time structure of ionospheric radio noise bursts drifting in frequency have been performed taking into account the measurement conditions. It has been indicated that the model electron radio noise bursts agree with the measured bursts reflecting from the ionosphere at altitudes of 100–180 km. The model of the monoenergetic beam of electrons precipitating from the radiation belt (L ～ 2.0–2.8) into the ionosphere has been proposed. 相似文献
11.
S.S. De B.K. De B. Bandyopadhyay Suman Paul D.K. Haldar S. Barui 《Journal of Atmospheric and Solar》2010,72(11-12):829-836
The variation of the first Schumann resonance (SR) frequency spectra observed from the recorded data over Kolkata (22.56°N, 88.5°E) during a solar proton event (SPE) on July 14, 2000 has been presented. It shows increase in frequency during X-ray bursts and decrease during the period of occurrence of an SPE. The results from some other locations for the same event are also reported. The severe X-ray bursts recorded just before the proton event exhibit enhancement in frequency of the first mode due to enhancement of ionization in the D-region of the ionosphere. Some attempts are made to explain the observed variation during solar proton events in terms of the perturbations within the Earth–ionosphere waveguide on the basis of two-layer-model. 相似文献
12.
Lower portion of the ionosphere known as the D-layer has properties of Gaussian random plane affecting very low frequency waves. This is manifested by stochastic properties of reflected VLF waves as their auto-correlation function (ACF) in time is the Bessel function of the first kind and zero order. In this paper, we show that the properties of this Bessel function are connected with the seismic activity in the area near the great circle path of VLF waves. 相似文献
13.
根据波形形态和特性,分析爆破、压路机、夯锤造成的振动特征.结果显示,爆破波形显示瞬间脉冲形,具有较大幅值;压路机波形平稳,三分向主频范围区域较小;夯锤波形显示瞬间脉冲,但三分向主频基本相似. 相似文献
14.
Summary Wave diagnostics of several alternatives of a constructed model of the daytime and night ionosphere of the mid geomagnetic latitudes were carried out in the ULF range of electromagnetic waves. The altitude profiles of local wave parameters of the ionosphere, the wavelengths and wave attenuation, were analysed at a fixed frequency. The frequency dependence of the amplitude and polarization characteristics of the total wave at the Earth's surface were also analysed in dependence on the frequency-amplitude spectrum of geomagnetic pulsations. The effect of the low regions of the ionosphere (h<100 km) was tested on the damping of the propagating wave and on the frequency-amplitude and polarization characteristics of the wave at the Earth's surface. 相似文献
15.
B. G. Gavrilov Yu. I. Zetzer V. I. Kurkin I. E. Markovich Yu. V. Poklad M. Parrot I. A. Ryakhovskii V. V. Yakim 《Izvestiya Physics of the Solid Earth》2012,48(4):354-362
Variations in the geomagnetic and electric fields and variations of the total electron content (TEC) of the ionosphere recorded
in the Baikal Rift Zone (BRZ) during the expeditions in 2009 and 2010 are analyzed. Synchronous bursts in the geomagnetic
field on the ground and in the ionosphere, which are caused by propagation of electromagnetic disturbances (spherics) generated
by the remote lightning discharges, are revealed. The analysis of the occurrence frequency of the electromagnetic disturbances
at an altitude of ∼700 km shows that there is a preferred region of predominant propagation of these disturbances from the
Earth-ionosphere waveguide to the upper ionosphere. When the ionospheric penetration point moves through this preferred region,
the frequency spectrum of TEC variations changes, and the northern boundary of the region of spectral alteration is located
at ∼54°N. The bursts in TEC that map on the zones of the main faults in the Tunka valley are identified. The results probably
suggest a relation between the electromagnetic phenomena in the ionosphere and the structures in the lithosphere. 相似文献
16.
E. D. Tereshchenko A. E. Sidorenko V. F. Grigor’ev A. A. Zhamaletdinov 《Geomagnetism and Aeronomy》2010,50(5):655-660
The amplitudes of variations in the magnetic and electric fields at extremely low frequencies were studied on the Kola Peninsula
during a five-day-long experiment under different geophysical conditions. These studies demonstrated that the influence of
the ionosphere is distinguishable at frequencies of <10 Hz and the structure of field variations reflected by the ionosphere
is similar to that of the transverse wave. It is established that the ratio between semimajor axes of polarization ellipses
of the electric and magnetic fields is independent of the state of the ionosphere and is likely determined by the deep structure
of the crust beneath the site of the experiment. 相似文献
17.
Anisotropic elastic full‐waveform inversion of walkaway vertical seismic profiling data from the Arabian Gulf 
下载免费PDF全文
下载免费PDF全文 John C Owusu Marwan Charara Scott Leaney Allan Campbell Shujaat Ali Igor Borodin Les Nutt Henry Menkiti 《Geophysical Prospecting》2016,64(1):38-53
Borehole seismic addresses the need for high‐resolution images and elastic parameters of the subsurface. Full‐waveform inversion of vertical seismic profile data is a promising technology with the potential to recover quantitative information about elastic properties of the medium. Full‐waveform inversion has the capability to process the entire wavefield and to address the wave propagation effects contained in the borehole data—multi‐component measurements; anisotropic effects; compressional and shear waves; and transmitted, converted, and reflected waves and multiples. Full‐waveform inversion, therefore, has the potential to provide a more accurate result compared with conventional processing methods. We present a feasibility study with results of the application of high‐frequency (up to 60 Hz) anisotropic elastic full‐waveform inversion to a walkaway vertical seismic profile data from the Arabian Gulf. Full‐waveform inversion has reproduced the majority of the wave events and recovered a geologically plausible layered model with physically meaningful values of the medium. 相似文献
18.
This paper describes the results of a preliminary study to determine the effective heating and cooling time constants of ionospheric currents in a simulated modulated HF heating, ‘beam painting’ configuration. It has been found that even and odd harmonics of the fundamental ELF wave used to amplitude modulate the HF heater are sourced from different regions of the ionosphere which support significantly different heating and cooling time constants. The fundamental frequency and its odd harmonics are sourced in a region of the ionosphere where the heating and cooling time constants are about equal. The even harmonics on the other hand are sourced from regions of the ionosphere characterised by ratios of cooling to heating time constant greater than ten. It is thought that the even harmonics are sourced in the lower ionosphere (around 65 km) where the currents are much smaller than at the higher altitudes around 78 km where the currents at the fundamental frequency and odd harmonics maximise. 相似文献
19.
20.
Sufficient low‐frequency information is essential for full‐waveform inversion to get the global optimal solution. Multi‐scale envelope inversion was proposed using a new Fréchet derivative to invert the long‐wavelength component of the model by directly using the low‐frequency components contained in an envelope of seismic data. Although the new method can recover the main structure of the model, the inversion quality of the model bottom still needs to be improved. Reflection waveform inversion reduces the dependence of inversion on low‐frequency and long‐offset data by using travel‐time information in reflected waves. However, when the underground medium contains strong contrast or the initial model is far away from the true model, it is hard to get reliable reference reflectors for the generation of reflected waves. Here, we propose a combination inversion algorithm, i.e., reflection multi‐scale envelope inversion, to overcome the limitations of multi‐scale envelope inversion and reflection waveform inversion. First, wavefield decomposition was introduced into the multi‐scale envelope inversion to improve the inversion quality of the long‐wavelength components of the model. Then, after the initial model had been established to be accurate enough, migration and de‐migration were introduced to achieve multi‐scale reflection waveform inversion. The numerical results of the salt‐layer model and the SEG/EAGE salt model verified the validity of the proposed approach and its potential. 相似文献