A majority of above papers are based on the data over rel- atively short distance (distance is from 1 Mm to a few Mm) propagation. We have presented a very convincing evidence on ionospheric perturbations associated with the Kobe EQ (Hayakawa et al., 1996), and this finding was based on the daily trace of the terminator times (TTs) by using the Omega VLF transmitter located at Tsushima and by receiving this signal at Inubo. The TT is defined as a time when the diurnal variation of amplitude (or phase) shows a minimum around the local sunset or sunrise. The distance between the VLF transmitter and receiver for the Kobe case is only 1 Mm, and we have interpreted the shift in TTs in term of the lowering of the lower ionosphere before the EQ (Hayakawa et al., 1996; Molchanov and Hayakawa et al., 1998; Yoshida et al., 2008). The shift of this TT effect has been investigated by Clilverd et al. (1999) for an extremely long (more than 10 Mm) NS prop- agation path, and concluded that there existed no seismo- ionospheric perturbation and that the TT method is not useful in finding out seismo-ionospheric perturbations. It is rather easy for us to consider that it is reasonable for them to have detected no TT anomaly on their long propagation path on
Near surface sources causing large vertical displacement of the earth surface during strong earthquakes are often known to excite the atmospheric infrasonic waves (e.g. Blanc, 1985) that propagate upward with increasing am- plitude. Ionospheric disturbances induced by severe earth- quakes have been reported by, Yuen et al. (1969), Blanc (1985), Tanaka et al. (1984) and Wolcott et al. (1984), Calais and Minister, (1995), Hobara and Parrot, (2005), Artru et al. (2005). The measurement of ionospheric To- tal Electronic Content (TEC) by using Global Positioning System (GPS) transmission have been used by Calais and Minister, (1995) to show the ionospheric response to the Northridge earthquake (Southern California) on January 17, 1994 (M w = 6.7). The present paper reports a preliminary study on ionospheric perturbations observed subsequent to
these conditions being extremely favourable for inducing ionospheric perturbations (e.g., Hayakawa et al., 2010a). The epicentre was located about 15 km west-south-west of the capital of Port-France of the Republic of Haiti. This area is characterised by the proximity to the collisional boundary between the North American and Caribbean plates, where we expect very often shallow, inland EQs. The fault responsible for this EQ is considered to be one in the Enriquillo-Plaintain Garden fault system. Two significant aftershocks took place; the first one occurred at 17:00 on 12 January (LT) just after the main shock and another at 06:03 LT on 20 January (about 8 days after the main shock). Both aftershocks had a magnitude of 5.9. There were reports of many casualties caused by this EQ; 220 000 people died and 320 000 people were injured.
As is shown in Fig. 1, a VLF/LF transmitter emits elec- tromagnetic waves at a particular frequency mainly in the subionospheric waveguide, which are used to infer the seismo-ionospheric perturbations as mentioned above (e.g., Hayakawa et al., 1996; Molchanov and Hayakawa, 1998). While, another part of VLF/LF transmitter signals is known to penetrate upward into the ionosphere/magnetosphere in whistler mode (Hayakawa, 1995). This kind of whistler- mode VLF transmitter signal is also expected to provide us with further information on the seismo-ionospheric per- turbation because of their penetration through this region. In fact, Molchanov et al. (2006) have recently found sig- nificant seismo-ionospheric effects associated with a huge Sumatra EQ in December, 2004 by using the VLF data ob- served on board the French satellite, DEMETER. And, this satellite finding is found to be in good consistence with our ground-based VLF observation for the same EQ by Horie et al. (2007a, b). This paper is a further extension of the paper by Molchanov et al. (2006), which deals with further event studies for Japanese EQs by using the same DEME- TER VLF/LF wave data. The satellite, DEMETER was launched on 29 June 2004, and it is working well with the aim of studying seismo-electromagnetic effects (Parrot et al., 2006). In this paper we have chosen several large Japanese EQs including the Miyagi-oki EQ (16 August 2005; M=7.2, depth=36 km), and the target transmitter is a Japanese LF transmitter (JJY) whose transmitter frequency is 40 kHz and which is located in Fukushima prefecture (Hayakawa, 2004).
Abstract. As the target earthquake we have taken a huge earthquake (EQ) named Miyagi-oki earthquake on 16 Au- gust 2005 (with magnitude of 7.2) and we have analyzed the 4 month period including the date of this EQ. In addition to our previous analysis on the nighttime average amplitude (trend) and nighttime fluctuation, we have proposed the use of fluctuation power spectra in the frequency rage of atmo- spheric gravity waves (period=10 min to 100 min) as a third parameter of subionospheric VLF/LF propagation character- istics. Then it is found that this third parameter would be of additional importance in confirming the presence of seismo- ionospheric perturbations. Finally, we have discovered an important role of lunar tidal effect in the VLF/LF data, which appears one and two months before this large EQ.
Here, the reception on board the DEMETER satellite of the VLF signals radiated by ground transmitters is analyzed. In the past, the reception of such signals was undertaken on many satellites for the investigation of the VLF wave prop- agation and of the interaction with the ionospheric plasma (Aubrey, 1968; Inan and Helliwell, 1982; Molchanov, 1985). The present analysis can be considered as a new method of ionospheric sounding in association with the seismic activity. It was suggested among the perspectives of the DEMETER satellite, whose major scientific objectives are the study of
The fluctuation spectra of the different kinds of seismo- electromagnetic phenomena would provide essential in- formation on the modulation taken place at different regions (including the lithosphere, atmosphere, iono- sphere/magnetosphere and sun). The presence (or existence) of seismogenic electromagnetic phenomena, itself is still controversial, so that the modulation in the lithosphere and atmosphere would provide an additional confirmation that those effects are really seismogenic. Also, such modulation effects would be of extreme importance in obtaining further hints on the generation mechanisms of seismo- electromagnetic effects (ULF emissions, seismo-ionospheric perturbations, etc.). Apart from the previous conspicuous modulation periodicities, some other useful information embedded in the time-series data can be extracted from the slope of fluctuation spectra or fractal analysis, which would be useful for the study of self-organized criticality in the lithosphere and its effects even onto the ionosphere.
measurement of the electric field, IMSC for the measurement of the magnetic field, IAP a plasma analyzer, IDP a particle detector, and ISL, a set of two Langmuir probes. In primary studies, many anomalous phenomena have been recorded by the DEMETER satellite (Parrot et al., 2006; Sarkar et al., 2007; Bhattacharya et al., 2007), which illustrated that strong earthquakes could induce ionospheric perturbations. The Wenchuan 8.0 earthquake, located at 30.97 ◦ N, 103.57 ◦ E, took place on 12 May 2008, and, in this paper, we used the DEMETER data to search for a precursor of this earthquake in the ionosphere.
The sole method to monitor the former lower ionosphere perturbation is the use of VLF/LF (very low frequency/low frequency) sounding. The amplitude (and/or phase) of subionospheric signals from any VLF/LF transmitters are con- tinuously monitored, and the observed signal parameters are mainly determined by the position of reflection height which depends on the value and gradient of electron density. It is typically 80 km in daytime and is about 90 km at night. This VLF/LF method can provide us with the information on the perturbation in the lower ionosphere, which has been found to be very promising for the short-term EQ prediction , because such VLF propagation anomalies tend to appear about one week before an EQ. Since the pioneering works by Russian and Japanese   , there have been published many papers on the use of VLF/LF method for the study of the seismo-ionospheric perturbations (see, our latest review ), and this VLF method is becoming a world trend for short-term EQ prediction as understood from the establishments of VLF net- works in different countries    being stimulated by our Japanese network  .
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Abstract. The present study reports the VLF (very low fre- quency) sub-ionospheric perturbations observed on transmit- ter JJI (22.1 kHz), Japan, received at the Indian low-latitude station, Allahabad ( geographic lat. 25.41 ◦ N, long 81.93 ◦ E), due to Wenchuan earthquake (EQ) that occurred on 12 May 2008 with the magnitude 7.9 and at the depth of 19 km in Sichuan province of Southwest China, located at 31.0 ◦ N, 103.4 ◦ E. The nighttime amplitude fluctuation analysis gives a significant increase in fluctuation and dispersion two days before EQ, when it crosses 2σ criterion. However, there was no significant change observed in the amplitude trend. The diurnal amplitude variation shows a significant increase in the amplitude of JJI signal on 11 and 12 May 2008. The grav- ity wave channel and changes in the electric field associated with this EQ seem to be the potential factors of the observed nighttime amplitude fluctuation, dispersion, and significant increase in the signal strength.
currently in need of GPS for many applications, but India is located near the equatorial ionospheric belt so it is necessary to improve the accuracy of GPS over the Indian region . In order to improve the positional accuracy of GPS, the ISRO along with Airport Authority of India has implemented the space based augmentation system called GAGAN . The positional accuracy of GPS is continuously monitored and corrected by the Indian ground reference stations. The GAGAN ensures the good positional accuracy, continuity, availability of GPS signal over the Indian region. The receiver manufacturer’s from India prefers the GAGAN augmentation system in order to provide the good positional accuracy to the civilians in India. The certification process of GAGAN is under progress and in future, the GAGAN enabled receiver will ensures a good positional accuracy over the Indian region .
The present work been carried out under the project titled ‘Development of Single Frequency Ionospheric correction & plasma bubble detection algorithms using GPS Aided GEO Augmented Navigation (GAGAN) & Navigation Indian Constellation (NavIC) TEC observations’ sponsored by NavIC– GAGAN Utilization Programme at Space Applications Centre, Ahmedabad, India, Project ID: NGP- 10.
The most important and influential ionospheric pioneer in Germany was certainly Jonathan Zenneck (1871–1959), Karl Rawer called him the “father of the German ionospheric physics”. Zenneck first studied theology and natural sci- ences at the University of Tübingen from 1889 to 1894 and received a PhD in zoology. He almost decided to be- come a zoologist, but discussions with the above mentioned K. F. Braun aroused his interest in HF techniques and he be- came an assistant of Braun at the University of Straßburg from 1895–1905. During this time he performed his first ex- periments in wireless telegraphy in order to establish a mar- itime radio service at the shore of the North Sea in Cuxhaven. In 1905 he published a textbook on wireless telegraphy, the first of this kind in Germany.
In recent years, the Department of Lands (DOL) in Thailand has been establishing the Virtual Reference Station (VRS) - NRTK system mainly to support cadastral surveying applications. The DOL VRS network comprises of 11 reference stations located in the Central Plain region with spacing ranging from 27.8 to 125.6 km, the average spacing is around 60 km. The performance of the DOL VRS network was tested using a static mode for rover antennas . The test results revealed that in general the horizontal positioning accuracy could be achieved within 4 cm when the ambiguity-fixed solutions were available. However, many large positioning jumps were observed in the local pre-midnight period even with the ambiguity-fixed solutions. It is also important to note that the ambiguity-fixed solutions could be obtained only 80% of the time. This percentage is relatively low compared to other NRTK services. Since Thailand is in a low-latitude region, atmospheric bias is especially problematic. This is due to the fact that ionospheric activity is much higher in a low-latitude region than in a mid-latitude region . Previous studies  and  have shown the variation of ionospheric activity in Thailand region and confirmed that ionospheric irregularities usually occur at night time.  found that the ionospheric height varies anomaly in the night time with the occurrence of the spread F, they seems to be related.  stated that the pre-midnight scintillation occurrence is inhibited by magnetic activity. Considering the high variation of ionospheric effect in this region, mitigating ionospheric bias through the use of 60-km reference station spacing may not provide reliable and accurate positioning solutions. This paper aims to test the performance of NRTK in Thai region on the basis of reference station spacing by incorporating the use of all available Continuous GPS (CGPS) stations in the central part of Thailand. In the following sections, the GPS data and software used are briefly described. The data processing is explained, followed by a discussion of the test results. Finally, some concluding remarks are given.
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tives of both metric and Galileon field. The DPSV approach makes use of the Einstein equations (7) in order to get rid of the second derivatives of metric perturbations, so that there is only one scalar degree of freedom left (with second derivatives) in the resulting Galileon equation. It is easy to see, that in eqs. (6) and (7) all the second derivatives of metric got contracted into gravitational tensors. In what follows, we assume that the Ricci tensor and scalar are transformed into the Riemann tensor in both eqs. (6) and (7), which simplifies our argument.
inclination. The special perturbations analysis therefore assumes that the normal component of acceleration direction varies as a step, moving from positive to negative every half orbit, while the tangential component of acceleration direction remains constant and the radial component of acceleration direction is always equal to zero. This special perturbations technique numerically propagates the spacecraft position by integration of the modified equinoctial equations of motion in the Gauss’ form [14, 15]. This is done using an explicit, variable step-size Runge-Kutta (4, 5) formula, the Dormand-Prince pair (a single step method) .
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structure of density should be observed because the elec- tric field prefers to transport along the magnetic field. In this paper, we simulated the electron density structure of nighttime MSTID by Otsuka et al. (2013) and suc- cessfully reconstructed the MSTID density structure by the GPS tomography. It indicates the capability of GPS tomography for the studies of disturbed ionosphere, such as the MSTID. In the future, the developed algorithm of GPS tomography in this paper will be used to reconstruct the three-dimensional electron density structure by the real GPS-TEC observations from GEONET and further provide the near-real-time ionospheric density structure over Japan. In the present version of GPS tomography process, it needs around 30 min (including the GPS-TEC calculation and the reconstruction times) to reproduce the 3D structure of electron density. A Python version of GPS tomography is ongoing to develop to speed up the whole processes. The first result shows the time can be reduced to around 5 min, which could make the “near real time” possible after the program being completed.
A low level of noise is initially added to the system to accelerate the pattern-forming process. The reason for filtering the noise is to accommodate (as closely as possible) the periodic bound- ary conditions required by FFTs. Filtering is achieved by multiplying a white noise profile by a Gaussian function in Fourier space. Attenuating the highest frequencies produces coloured noise which is then implemented in the simulation. We note that patterns would still emerge without this random component to the initial solution (with finite numerical accuracy providing symmetry-breaking perturbations), but many tens (or hundreds) of thousands of transits may be required. Pattern formation in the bulk ring cavity is qualitatively similar to that in the FP problem, with allowed spatial frequencies competing for growth. Eventually, however, the most-unstable frequency K 0 will dominate since it has the lowest threshold and therefore the
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In conclusion, we have shown that the electrostatic profile of ionized donors strongly affects the interference of electron waves in semiconductor billiards. By demon- strating this effect for two material systems and different fabrication methods, we propose this is a generic limita- tion of semiconductor billiards. This contradicts previ- ous models in which the quantum dynamics was inter- preted as being determined purely by the billiard walls [22–27, 51] and which predict that the MCF should be robust to thermal cycling. In contrast to this traditional billiard picture, our experiments show that the modu- lation doping technique does not reduce the donor elec- trostatic perturbations sufficiently to ignore their pres- ence. In particular, we have demonstrated experimen- tally that the sensitivity of the AB effect, highlighted by semi-classical theory developed for diffusive regime , extends to billiards even though the size of the electro- static perturbations in billiards is reduced significantly compared to diffusive systems.
From the above discussion, we can conclude that the ionospheric effect which is entrenched at a height of 80-400km from the earth surface is more influences the GPS precision when compared with the other parameters. It is illustrated in table 5 along with which parameters that influence the existing methods. We can observe that the Kalman filter method has been able to soothe four parameters influencing the GPS precision from table 5. Recursive Least Squares and Map matching algorithm do not affect the parameters mentioned that influence GPS precision. However, in other aspects such as efficient interface on map applications, both of these techniques could enhance GPS monitoring operations. Reference station network enhances GPS precision can only decrease two parameters affecting GPS precision. Lastly, only three GPS inaccuracy parameters can be corrected by the PGPS method  . Consequently, the best approach which can improve the precision of GPS is the Kalman Filter and Reference Stations Network can be recommended as an elective approach to enhance GPS precision too. As per the Kalman filter, it is a direct recursive approach used for both linear and nonlinear estimations. It can be used to smoothen the positioning errors occurred by various parameters which influence the GPS precision.