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Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.


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Journal ArticleDOI
TL;DR: In this article, the authors proposed a semianalytical method for evaluating the near-zone field of a very low frequency (VLF) electric dipole in a homogeneous and anisotropic plasma.
Abstract: In this paper, we proposed a semianalytical method for evaluating the near-zone field of a very low frequency (VLF) electric dipole in a homogeneous and anisotropic plasma. Due to the different attenuation properties for the ordinary wave (O-wave) and the extraordinary wave (E-wave), the integrals corresponding to their contributions should be truncated at different locations of the real axis and need to be separately treated. By applying the complex function theory and a speed-up convergence algorithm, the original oscillating integral for the near-field is transformed into two fast convergent integrals plus an analytical solution. Computations show that, in the near zone, the O-wave still has comparable amplitudes with the E-wave, and its influence on the total field should not be neglected. It is also observed from the radiation pattern that there exists a pronounced “cohesion effect” for the E-wave along the direction of the geomagnetic field, while the phase mutations of the O-wave exactly coincide with the minima of its field strength. Moreover, it is found that the radiation ability of a VLF electric dipole in an anisotropic plasma will increase with the operating frequency.

16 citations

Journal ArticleDOI
TL;DR: In this paper, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76 deg S, 84 deg W), during a geomagnetically disturbed period (Kp = 6-) with intense X-ray and VLF chorus activity.
Abstract: On January 4, 1978, at 1140 UT, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76 deg S, 84 deg W), during a geomagnetically disturbed period (Kp = 6-) with intense X-ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10-minute duration. These data have been correlated with measurements of FLF chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis fo the data did indicate a significant correlation between the Siple X-ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 + or 0.3.

16 citations

Book ChapterDOI
01 Jan 2014
TL;DR: The very low-frequency (VLF) electromagnetic (EM) method is the simplest EM method to delineate shallow subsurface conducting structures, and it is suitable to depict conducting structures up to 200 m depth in highly resistive terrain this article.
Abstract: The very low-frequency (VLF) electromagnetic (EM) method is the simplest EM method to delineate shallow subsurface conducting structures. Since the approach utilizes signals transmitted from worldwide transmitters located in coastal areas in the 5–30 kHz frequency band, it is suitable to depict conducting structures up to 200 m depth in highly resistive terrain. Freely and readily available primary field signals anywhere around the Earth make the VLF method very convenient and efficient for field data collection. Further, VLF data processing using digital linear filtering is quite accurate and very efficient in depicting the qualitative information about subsurface conductors, even though quantitative interpretation of VLF data is as complex as other EM data interpretation. In the present study, various aspects of the VLF method such as basic theory, worldwide VLF transmitters, quantities measured, and interpretation procedures are discussed in detail. Finally, the efficacy of the VLF method for groundwater investigation, mineral investigation, and landslide and subsurface pollution monitoring studies has been demonstrated. Even though the VLF method is a rapid technique for subsurface investigation, use of complementary geophysical methods such as gravity, direct current (DC) resistivity, self-potential, radiometric, etc., reduces the ambiguity in the interpretation and yields reliable subsurface information.

16 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported the VLF sub-ionospheric perturbations observed on transmitter 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.
Abstract: . The present study reports the VLF (very low frequency) sub-ionospheric perturbations observed on transmitter 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 gravity 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.

15 citations

Patent
13 Jul 1973
TL;DR: In this paper, a super short pulse, VLF/LF ionosounder transmits signals which arrive at a distant receiver both by traveling over the earth's surface and by reflection from the ionosphere.
Abstract: A high resolution, super short pulse, VLF/LF ionosounder transmits signals which arrive at a distant receiver both by traveling over the earth's surface and by reflection from the ionosphere. There is radiated such short pulses that the groundwave, which arrives at the receiver first, has past before the arrival of the skywave signal, giving a clean separation between the ground and skywave signals thus making it possible to study uncontaminated individual skywave reflections and also making possible very high resolution. Amplitude and phase information may be recovered by frequency or time domain processing.

15 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202232
202156
202048
201942
201852