Topic
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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TL;DR: In this paper, the authors proposed a possible use of VLF/LF (very low frequency (3-30 kHz) /low frequency (30-300 kHz)) radio sounding of the seismo-ionospheric perturbations.
Abstract: It is recently recognized that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes, seems to be very promising for short-term earthquake prediction. We have proposed a possible use of VLF/LF (very low frequency (3-30 kHz) /low frequency (30-300 kHz)) radio sounding of the seismo-ionospheric perturbations. A brief history of the use of subionospheric VLF/LF propagation for the short-term earthquake prediction is given, followed by a significant finding of ionospheric perturbation for the Kobe earthquake in 1995. After showing previous VLF/LF results, we present the latest VLF/LF findings; One is the statistical correlation of the ionospheric perturbation with earthquakes and the second is a case study for the Sumatra earthquake in December, 2004, indicating the spatical scale and dynamics of ionospheric perturbation for this earthquake.
135 citations
TL;DR: In this article, the authors present further experimental results on ionospheric current modulation, using powerful amplitude modulated HF waves produced by the new heating facility at Ramfjordmoen near Tromso, Norway.
128 citations
Patent•
24 Jan 2003
TL;DR: In this article, a radio-acoustic sounding system for providing wind measurements at altitudes of 100 meters or less is presented, where the frequency of the audio pulse is selected to have a wavelength that is one-half the wavelength of the electromagnetic energy transmitted by the antenna or antennas.
Abstract: The present invention is directed to a radio-acoustic sounding system for providing wind measurements at altitudes of 100 meters or less. Wind measurements are obtained by transmitting a pulse of audio frequency energy through one or more volumes corresponding to the coverage area of one or more radio frequency transceivers. The frequency of the audio pulse is selected to have a wavelength that is one-half the wavelength of the electromagnetic energy transmitted by the antenna or antennas. By monitoring a return radio frequency signal at selected times following the transmission of the audio pulse, wind data is obtained at selected altitudes. Wind speed and direction can be obtained by observing the Doppler frequency shift of return radio frequency signals, or by observing the amplitude of the return radio frequency signals. In accordance with an embodiment of the present invention, precipitation measurements may be made by transmitting a radio frequency signal at the same radio frequency as is used in connection with wind measurements, and observing return radio frequency signals.
128 citations
TL;DR: In this article, a geostationary satellite GEOS-2 above Africa (longitude 37°E) and the polar-orbiting satellite Aureol-3 (apogee 2012 km, perigee 408 km, inclination 82°5′, period 109.5 min).
126 citations
TL;DR: In this article, the phase delay suffered by VLF radio waves propagating over large distances in the Earth-ionosphere waveguide revealed the presence of ionization in the night-time lower ionosphere produced by X-rays from the strong X-ray source, Scorpius XR-1.
Abstract: A RECENT article by Edwards et al.1 suggested that observations of the phase delay suffered by VLF radio waves propagating over large distances in the Earth–ionosphere waveguide revealed the presence of ionization in the night-time lower ionosphere produced by X-rays from the strong X-ray source, Scorpius XR-1. and other weaker sources in the vicinity of the galactic centre. These observations were taken on the 20 kHz transmissions from WWVL, Boulder, recorded in New Zealand.
125 citations