The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Martin Füllekrug - One of the best experts on this subject based on the ideXlab platform.
-
multipath propagation of low frequency Radio Waves inferred from high resolution array analysis
Radio Science, 2015Co-Authors: Martin Füllekrug, N D Smith, Andrew Mezentsev, Robert J Watson, Ivan Astin, Stephane Gaffet, A N Evans, Michael J RycroftAbstract:The low frequency Radio sky shows the locations of electromagnetic Radio sources with a characteristic dilution of precision. Here we report a thorough high resolution analysis of Radio Waves from low frequency (∼20-150 kHz) Radio communication transmitters which are recorded with a small aperture array of Radio receivers during the day. It is found that the observed dilution of precision results from the array geometry of the Radio receivers, a birefringent wave propagation and the correlated multipath propagation of low frequency Radio Waves. The influence of the array geometry on the dilution of precision is reduced by taking into account the impulse response of the array. This procedure reveals for the very first time the splitting of one single Radio source into two distinct source locations separated by ∼0.2°-1.9° which result from a birefringent wave propagation. The two locations are yet more clearly identified by using the polarity of the modulated wave number vectors of the Radio Waves. This polarity is also used to quantify the dilution of precision arising from correlated multipath propagation which is discriminated against wave number fluctuations arising from the timing accuracy of the Radio receivers. It is found that ∼69% of the wave number variability is of natural origin and ∼31% originates from the timing accuracy of the receivers. The wave number variability from correlated multipath propagation results in a standard deviation ∼2-8% relative to the source location. This compact measurement of correlated multipath propagation is used to characterize the uncertainty of source locations in the Radio sky. The identification of correlated multipath propagation strongly suggests the existence of very fast processes acting on time scales <1 ms in the D-region ionosphere with physically meaningful effects on low frequency Radio wave propagation. This important result has implications for practical applications in that the observed multipath propagation enables the determination of natural limits for the accuracy of navigation and lightning location methods using low frequency Radio Waves.
-
Multipath propagation of low-frequency Radio Waves inferred from high-resolution array analysis
Journal of Nuclear and Radiochemical Sciences, 2015Co-Authors: Martin Füllekrug, Andrew Mezentsev, Ivan Astin, Stephane Gaffet, N. Smith, R. Watson, A. Evans, M. RycroftAbstract:The low-frequency Radio sky shows the locations of electromagnetic Radio sources with a characteristic dilution of precision. Here we report a thorough high-resolution analysis of Radio Waves from low-frequency (∼20–150 kHz) Radio communication transmitters which are recorded with a small aperture array of Radio receivers during the day. It is found that the observed dilution of precision results from the array geometry of the Radio receivers, a birefringent wave propagation, and the correlated multipath propagation of low-frequency Radio Waves. The influence of the array geometry on the dilution of precision is reduced by taking into account the impulse response of the array. This procedure reveals for the very first time the splitting of one single Radio source into two distinct source locations separated by ∼0.2°–1.9° which result from a birefringent wave propagation. The two locations are yet more clearly identified by using the polarity of the modulated wave number vectors of the Radio Waves. This polarity is also used to quantify the dilution of precision arising from correlated multipath propagation which is discriminated against wave number fluctuations arising from the timing accuracy of the Radio receivers. It is found that ∼69% of the wave number variability is of natural origin and ∼31% originates from the timing accuracy of the receivers. The wave number variability from correlated multipath propagation results in a standard deviation ∼2–8% relative to the source location. This compact measurement of correlated multipath propagation is used to characterize the uncertainty of source locations in the Radio sky. The identification of correlated multipath propagation strongly suggests the existence of very fast processes acting on time scales
-
experimental simulation of satellite observations of 100 khz Radio Waves from relativistic electron beams above thunderclouds
Atmospheric Chemistry and Physics, 2011Co-Authors: Martin Füllekrug, Christian Hanuise, Marc ParrotAbstract:Relativistic electron beams above thunderclouds emit 100 kHz Radio Waves which illuminate the Earth's at- mosphere and near-Earth space. This contribution aims to clarify the physical processes which are relevant for the spa- tial spreading of the Radio wave energy below and above the ionosphere and thereby enables an experimental simulation of satellite observations of 100 kHz Radio Waves from rel- ativistic electron beams above thunderclouds. The simula- tion uses the DEMETER satellite which observes 100 kHz Radio Waves from fifty terrestrial Long Range Aid to Naviga- tion (LORAN) transmitters. Their mean luminosity patch in the plasmasphere is a circular area with a radius of 300 km and a power density of 22 µW/Hz as observed at 660 km height above the ground. The luminosity patches exhibit a southward displacement of 450 km with respect to the lo- cations of the LORAN transmitters. The displacement is reduced to 150 km when an upward propagation of the Radio Waves along the geomagnetic field line is assumed. This residual displacement indicates that the Radio Waves undergo 150 km sub-ionospheric propagation prior to en- tering a magnetospheric duct and escaping into near-Earth space. The residual displacement at low (L 2.14) geomagnetic latitudes ranges from 100 km to 200 km which suggests that the smaller inclination of the geomagnetic field lines at low latitudes helps to trap the ra- dio Waves and to keep them in the magnetospheric duct. Dif- fuse luminosity areas are observed northward of the magnetic conjugate locations of LORAN transmitters at extremely low geomagnetic latitudes (L< 1.36) in Southeast Asia. This re- sult suggests that the propagation along the geomagnetic field lines results in a spatial spreading of the Radio wave energy over distances of 1 Mm. The summative assessment of the electric field intensities measured in space show that nadir observations of terrestrial 100 kHz Radio Waves, e.g., from relativistic electron beams above thunderclouds, are attenu- ated by at least 50 dB when taking into account a transiono- spheric attenuation of 40 dB.
-
Experimental simulation of satellite observations of 100 kHz Radio Waves from relativistic electron beams above thunderclouds
Atmospheric Chemistry and Physics, 2011Co-Authors: Martin Füllekrug, Christian Hanuise, Michel ParrotAbstract:Relativistic electron beams above thunderclouds emit 100 kHz Radio Waves which illuminate the Earth's atmosphere and near-Earth space. This contribution aims to clarify the physical processes which are relevant for the spatial spreading of the Radio wave energy below and above the ionosphere and thereby enables an experimental simulation of satellite observations of 100 kHz Radio Waves from rel-ativistic electron beams above thunderclouds. The simulation uses the DEMETER satellite which observes 100 kHz Radio Waves from fifty terrestrial Long Range Aid to Navigation (LORAN) transmitters. Their mean luminosity patch in the plasmasphere is a circular area with a radius of ∼300 km and a power density of ∼22 µW/Hz as observed at ∼660 km height above the ground. The luminosity patches exhibit a southward displacement of ∼450 km with respect to the locations of the LORAN transmitters. The displacement is reduced to ∼150 km when an upward propagation of the Radio Waves along the geomagnetic field line is assumed. This residual displacement indicates that the Radio Waves undergo ∼150 km sub-ionospheric propagation prior to entering a magnetospheric duct and escaping into near-Earth space. The residual displacement at low (L < 2.14) and high (L > 2.14) geomagnetic latitudes ranges from ∼100 km to ∼200 km which suggests that the smaller inclination of the geomagnetic field lines at low latitudes helps to trap the Radio Waves and to keep them in the magnetospheric duct. Diffuse luminosity areas are observed northward of the magnetic conjugate locations of LORAN transmitters at extremely low geomagnetic latitudes (L < 1.36) in Southeast Asia. This result suggests that the propagation along the geomagnetic field lines results in a spatial spreading of the Radio wave energy Correspondence to: M. Füllekrug (eesmf@bath.ac.uk) over distances of ∼1 Mm. The summative assessment of the electric field intensities measured in space show that nadir observations of terrestrial 100 kHz Radio Waves, e.g., from relativistic electron beams above thunderclouds, are attenuated by at least ∼50 dB when taking into account a transiono-spheric attenuation of ∼40 dB.
-
Transionospheric attenuation of 100 kHz Radio Waves inferred from satellite and ground based observations
Geophysical Research Letters, 2009Co-Authors: Martin Füllekrug, Ivan Astin, Michel Parrot, Matthew Ash, Paul Williams, R. TalhiAbstract:Around fifty LORAN (LOng RAnge Navigation) transmitters in the northern hemisphere currently launch continuously pulsed 100 kHz Radio Waves into the Earth's atmosphere for marine navigation. It is discovered that the 100 kHz Radio Waves from the LORAN transmissions can be detected by the DEMETER satellite at an altitude of $660 km above the transmitters. These novel electric field measurements in space enable the determination of the nocturnal transionospheric attenuation by comparison with ground based electric field measurements. The electric field measurements on the satellite indicate that the nocturnal transionospheric attenuation of 100 kHz Radio Waves from LORAN transmissions is equivalent to a nocturnal subionospheric attenuation of the 100 kHz Radio Waves at a distance of $7-9 Mm. The Radio Waves exhibit an average subionospheric attenuation of $5 dB/Mm and it is concluded that the nocturnal transionospheric attenuation of 100 kHz Radio Waves is $35-45 dB. This result enables future space missions to quantify the intensity of lightning discharges associated with transient luminous events and terrestrial gray flashes.
Joseph L Kirschvink - One of the best experts on this subject based on the ideXlab platform.
-
sensory biology Radio Waves zap the biomagnetic compass
Nature, 2014Co-Authors: Joseph L KirschvinkAbstract:Weak Radio Waves in the medium-wave band are sufficient to disrupt geomagnetic orientation in migratory birds, according to a particularly well-controlled study. But the underlying biophysics remains a puzzle.
-
Radio Waves zap the biomagnetic compass
Nature, 2014Co-Authors: Joseph L KirschvinkAbstract:Weak Radio Waves in the medium-wave band are sufficient to disrupt geomagnetic orientation in migratory birds, according to a particularly well-controlled study. But the underlying biophysics remains a puzzle. See Letter p.353 Many migrating birds rely on the Earth's magnetic field for their sense of direction, although what mechanism they use to detect this extraordinarily weak field is unknown. Following the surprise observation that night-migratory songbirds (European robins) tested between autumn 2004 and autumn 2006 in wooden huts on the University of Oldenburg campus seemed unable to orient in the appropriate migratory direction, Henrik Mouritsen and colleagues performed controlled experiments to establish what was happening. They find that robins lose the ability to use the Earth's magnetic field when exposed to low-level AM electromagnetic noise between around 20 kz and 20 MHz, the kind of noise routinely generated by consumer electrical and electronic equipment. Interestingly, the magnetic component of this electromagnetic noise is a thousand times weaker than the lower exposure limits adopted in current World Health Organization (WHO) guidelines, yet it can disrupt the function of an entire sensory system in a higher vertebrate. The birds regain the ability to orient to the Earth's magnetic field when they are shielded from electromagnetic noise in the frequency range from 2 kHz to 5 MHz or when tested in a rural setting.
Michel Parrot - One of the best experts on this subject based on the ideXlab platform.
-
Precipitation of Energetic Electrons from the Earth’s Radiation Belt Stimulated by High-Power HF Radio Waves for Modification of the Midlatitude Ionosphere
Radiophysics and Quantum Electronics, 2020Co-Authors: V. L. Frolov, A. D. Akchurin, I. A. Bolotin, A. O. Ryabov, Jean-jacques Berthelier, Michel ParrotAbstract:Based on the results of the experiments performed in 2005–2010 within the framework of the Sura—DEMETER program, we analyze the features of the precipitations of energetic electrons (with energies E ≈ 100 keV) from the Earth’s radiation belt. The modification of the ionospheric F2 region was conducted by means of high-power HF O-mode Radio Waves radiated in the CW regime. The precipitations were detected using the equipment onboard DEMETER, a French microsatellite. The conditions of precipitation appearance were determined, and it was found that the electron precipitation region was stretched along the geomagnetic meridian to a distance of 1300 km; the size of the region in the transverse direction is about 400 km. It was shown by ionosonde measurements that such precipitations lead to increased absorption of Radio Waves in the lower ionosphere. It is assumed that the mechanism for precipitation of electrons from the Earth’s radiation belt is determined by the interaction of energetic electrons with VLF Radio Waves, which are generated due to the interaction of the amplitude-unmodulated O-mode pump wave with the ionospheric plasma near the wave reflection height.
-
precipitation of energetic electrons from the earth s radiation belt stimulated by high power hf Radio Waves for modification of the midlatitude ionosphere
Radiophysics and Quantum Electronics, 2020Co-Authors: V. L. Frolov, A. D. Akchurin, I. A. Bolotin, A. O. Ryabov, Jean-jacques Berthelier, Michel ParrotAbstract:Based on the results of the experiments performed in 2005–2010 within the framework of the Sura—DEMETER program, we analyze the features of the precipitations of energetic electrons (with energies E ≈ 100 keV) from the Earth’s radiation belt. The modification of the ionospheric F2 region was conducted by means of high-power HF O-mode Radio Waves radiated in the CW regime. The precipitations were detected using the equipment onboard DEMETER, a French microsatellite. The conditions of precipitation appearance were determined, and it was found that the electron precipitation region was stretched along the geomagnetic meridian to a distance of 1300 km; the size of the region in the transverse direction is about 400 km. It was shown by ionosonde measurements that such precipitations lead to increased absorption of Radio Waves in the lower ionosphere. It is assumed that the mechanism for precipitation of electrons from the Earth’s radiation belt is determined by the interaction of energetic electrons with VLF Radio Waves, which are generated due to the interaction of the amplitude-unmodulated O-mode pump wave with the ionospheric plasma near the wave reflection height.
-
Experimental simulation of satellite observations of 100 kHz Radio Waves from relativistic electron beams above thunderclouds
Atmospheric Chemistry and Physics, 2011Co-Authors: Martin Füllekrug, Christian Hanuise, Michel ParrotAbstract:Relativistic electron beams above thunderclouds emit 100 kHz Radio Waves which illuminate the Earth's atmosphere and near-Earth space. This contribution aims to clarify the physical processes which are relevant for the spatial spreading of the Radio wave energy below and above the ionosphere and thereby enables an experimental simulation of satellite observations of 100 kHz Radio Waves from rel-ativistic electron beams above thunderclouds. The simulation uses the DEMETER satellite which observes 100 kHz Radio Waves from fifty terrestrial Long Range Aid to Navigation (LORAN) transmitters. Their mean luminosity patch in the plasmasphere is a circular area with a radius of ∼300 km and a power density of ∼22 µW/Hz as observed at ∼660 km height above the ground. The luminosity patches exhibit a southward displacement of ∼450 km with respect to the locations of the LORAN transmitters. The displacement is reduced to ∼150 km when an upward propagation of the Radio Waves along the geomagnetic field line is assumed. This residual displacement indicates that the Radio Waves undergo ∼150 km sub-ionospheric propagation prior to entering a magnetospheric duct and escaping into near-Earth space. The residual displacement at low (L < 2.14) and high (L > 2.14) geomagnetic latitudes ranges from ∼100 km to ∼200 km which suggests that the smaller inclination of the geomagnetic field lines at low latitudes helps to trap the Radio Waves and to keep them in the magnetospheric duct. Diffuse luminosity areas are observed northward of the magnetic conjugate locations of LORAN transmitters at extremely low geomagnetic latitudes (L < 1.36) in Southeast Asia. This result suggests that the propagation along the geomagnetic field lines results in a spatial spreading of the Radio wave energy Correspondence to: M. Füllekrug (eesmf@bath.ac.uk) over distances of ∼1 Mm. The summative assessment of the electric field intensities measured in space show that nadir observations of terrestrial 100 kHz Radio Waves, e.g., from relativistic electron beams above thunderclouds, are attenuated by at least ∼50 dB when taking into account a transiono-spheric attenuation of ∼40 dB.
-
Transionospheric attenuation of 100 kHz Radio Waves inferred from satellite and ground based observations
Geophysical Research Letters, 2009Co-Authors: Martin Füllekrug, Ivan Astin, Michel Parrot, Matthew Ash, Paul Williams, R. TalhiAbstract:Around fifty LORAN (LOng RAnge Navigation) transmitters in the northern hemisphere currently launch continuously pulsed 100 kHz Radio Waves into the Earth's atmosphere for marine navigation. It is discovered that the 100 kHz Radio Waves from the LORAN transmissions can be detected by the DEMETER satellite at an altitude of $660 km above the transmitters. These novel electric field measurements in space enable the determination of the nocturnal transionospheric attenuation by comparison with ground based electric field measurements. The electric field measurements on the satellite indicate that the nocturnal transionospheric attenuation of 100 kHz Radio Waves from LORAN transmissions is equivalent to a nocturnal subionospheric attenuation of the 100 kHz Radio Waves at a distance of $7-9 Mm. The Radio Waves exhibit an average subionospheric attenuation of $5 dB/Mm and it is concluded that the nocturnal transionospheric attenuation of 100 kHz Radio Waves is $35-45 dB. This result enables future space missions to quantify the intensity of lightning discharges associated with transient luminous events and terrestrial gray flashes.
Michiko Hayano - One of the best experts on this subject based on the ideXlab platform.
-
Measurement of atmospheric water vapour on the ground's surface by Radio Waves
Hydrological Processes, 2001Co-Authors: Tokuo Kishii, Yasuhisa Kuzuha, Fumi Sugita, Michiko HayanoAbstract:Water vapour in the atmosphere and various meteorological phenomena are essential to the understanding of the mechanism of the water cycle. However, it is very difficult to observe water vapour in the atmosphere because the quantities are usually observed at a single point not over long intervals or in a specific plane or volume. Accordingly, the use of Radio Waves is considered to be necessary to observe water vapour. Radio Waves can be transmitted over long intervals and across large areas, and generally speaking, the characteristics of Radio Waves change due to material in the atmosphere, especially water vapour. Usually absorption is used to observe the quantity of water vapour. But the relationship between absorption and the quantity of water vapour is not linear, so we try to utilize the phase difference between two Radio Waves as an alternative method. First, the relationship between the phase delay and the water vapour was induced by a physical equation and the resulting phase delay was found to be proportional to the quantity of water vapour. Furthermore, the phase difference between two separate points was observed by use of two Radio Waves in the field, specifically 84 GHz and 245 GHz. For reference and comparison, water vapour density in the atmosphere was simultaneously observed by meteorological observation. As a result, the density of the water vapour was found to be proportional to the phase difference between the two Radio Waves. The result also shows that this method is able to measure the diurnal changes in water vapour density in each season. Copyright © 2001 John Wiley & Sons, Ltd.
M Mccarrick - One of the best experts on this subject based on the ideXlab platform.
-
unprecedentedly strong and narrow electromagnetic emissions stimulated by high frequency Radio Waves in the ionosphere
Physical Review Letters, 2009Co-Authors: Lars Norin, T B Leyser, Erik Nordblad, Bo Thide, M MccarrickAbstract:Experimental results of secondary electromagnetic radiation, stimulated by high-frequency Radio Waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from Radio Waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.