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Showing papers on "Very low frequency published in 1969"


Journal ArticleDOI
01 Jan 1969-Nature
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


Journal ArticleDOI
TL;DR: Poynting flux direction for proton whistlers determined from Injun 5 observations, obtaining data on source region and propagation in ionosphere as discussed by the authors, using Injun 4 observations.
Abstract: Poynting flux direction for proton whistlers determined from Injun 5 observations, obtaining data on source region and propagation in ionosphere

93 citations


Journal ArticleDOI
TL;DR: Injun 5 satellite VLF electric and magnetic fields observations, discussing antenna operation, Poynting flux and noise band measurements are discussed in this paper, where the antenna operation is discussed.
Abstract: Injun 5 satellite VLF electric and magnetic fields observations, discussing antenna operation, Poynting flux and noise band measurements

85 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of polar cap absorption events on the phase and amplitude of VLF transmissions were studied for the first time, and it was shown that normalization of (Δφ) with respect to frequency and affected length leads to two distinct linear relationships between (Ά) and (log log F/F0), where F is the proton flux as measured by satellites.

51 citations


Journal ArticleDOI
TL;DR: In this article, the authors conducted VLF walking trace whistlers and Doppler shifts in fixed frequency transmissions identified on OGO midlatitude spectrographic records, and found that they were correlated with the DoP shifts.
Abstract: Nonducted VLF walking trace whistlers and Doppler shifts in fixed frequency transmissions identified on OGO midlatitude spectrographic records

50 citations


Journal ArticleDOI
R. L. Smith1
25 Oct 1969-Nature
TL;DR: In this paper, the authors describe the auroral V-emission (AVE) phenomenon, which is a very low frequency (VLF) phenomenon that occurs in very high altitude (3,000 km) and with a low frequency minimum.
Abstract: AN interesting very low frequency (VLF) phenomenon which I shall call auroral V-emissions (AVEs) has been known for a number of years, although few reports have been published. The phenomenon has also been known informally as “short saucers” and “splashes”. The dynamic spectra of a collection of AVEs are shown in Fig. 1a. The AVEs shown here have a fairly low frequency minimum, near 0.5 kHz, and have time scales of the order of 10 s. The broader form at the upper part of the record may perhaps be an example of an AVE, but in this paper it will not be considered as an AVE. The name auroral V-emission is based on the region of observation and the V-shaped or hyperbolic spectral appearance. The hyperbolic shape is often quite symmetrical, particularly for the AVEs with shorter time scales. AVEs have only been observed in satellites, usually near the auroral zone. Noise bands with distinct intensity minima at harmonics of the local proton frequency are often observed at the centre of an AVE, especially for observations at relatively high altitude (3,000 km) and for AVEs with a low frequency minimum. The phenomena reported here have a much shorter time scale and a more well defined spectral appearance than the “V-type VLF hiss”1,2.

48 citations


Journal ArticleDOI
TL;DR: Ion depletion in high latitude exosphere, considering OGO 2 simultaneous observations of positive ion concentration, VLF signal propagation and whistlers, was reported in this paper, where it was shown that positive ion depletion in the exosphere is correlated with the number of whistlers.
Abstract: Ion depletion in high latitude exosphere, considering OGO 2 simultaneous observations of positive ion concentration, VLF signal propagation and whistlers

45 citations


01 Oct 1969
TL;DR: Very low frequency signals observed by OGO-4 measured and interpreted, and global ionospheric propagation study as mentioned in this paper, were used for the global ionosphere propagation study, which was conducted by the International Journal of Astronautics.
Abstract: Very low frequency signals observed by OGO-4 measured and interpreted, and global ionospheric propagation study

42 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the emissions are generated in the vicinity of the geomagnetic equator and exhibit a maximum or saturation intensity close to that predicted by Kennel and Petschek (1966).

34 citations


Journal ArticleDOI
TL;DR: In this article, the VLF phase disturbances and HF absorption observed during the proton events of August 28 and September 2, 1966, were quantitatively connected to the Proton intensities, energies, and cutoff latitudes observed by satellite 1963-38C, at 1100 km in a polar orbit.
Abstract: The VLF phase disturbances and HF absorption observed during the proton events of August 28 and September 2, 1966, were quantitatively connected to the proton intensities, energies, and cutoff latitudes observed by satellite 1963-38C, at 1100 km in a polar orbit. The connection is achieved through considerations that include a model of the ionospheric D region described in terms of an effective recombination coefficient related to the four generalized ionic reactions. The complementary use of the VLF and HF observations tends to reduce ambiguities often present in the formation of D-region models. The VLF is the more sensitive indicator of ionization effects due to solar protons in comparison to the HF absorption (especially at night) because the VLF responds to ionization enhancements over a relatively narrow altitude range varying with the proton energies and intensities.

32 citations


Journal ArticleDOI
TL;DR: In this paper, a case study is presented of the concurrent and apparently related behavior of four magnetospheric phenomena: whistler ‘ducts,’ cross-L drifts of tubes of ionization, an abrupt upper intensity cutoff of ducted whistlers at ƒHo/2.
Abstract: A case study is presented of the concurrent and apparently related behavior of four magnetospheric phenomena: (1) whistler ‘ducts,’ (2) cross-L drifts of tubes of ionization, (3) an abrupt upper intensity cutoff of ducted whistlers at ƒHo/2, where ƒHo is the minimum electron gyrofrequency along the path, and (4) artificial triggering of VLF whistler-mode noise at ƒ ∼ ƒHo/2. The event occurred on June 17, 1965, near local midnight, and involved the inward drift of a whistler duct through ∼0.2 L near L = 3. Triggering of magnetospheric noise by NAA transmissions at 17.8 kHz occurred when the minimum gyrofrequency on the drifting path became twice the NAA frequency.

Journal ArticleDOI
TL;DR: In this article, SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0-3 A, 0-8 A and 8-20 A bands were discussed.
Abstract: This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0–3 A, 0–8 A and 8–20 A bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3×10−5 ergs cm−2 sec−1 in the main ionizing band of 0–3 A. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 km, this beingα r≈6×10−6 cm3 sec−1; furthermore ion production rates were estimated during SPA's at heights below the reference level.

Book
01 Jan 1969
TL;DR: In this article, very low frequency propagation in magnetosphere from broadband VLF receivers on OGO 2 and OGO 4 polar satellites was conducted by using a very low-frequency (VLF) receiver.
Abstract: Nonducted very low frequency propagation in magnetosphere from broadband VLF receivers on OGO 2 and OGO 4 polar satellites

Journal ArticleDOI
TL;DR: In this article, Latitudinal cutoff of manmade VLF signals in short path through ionosphere to OGO 2 satellite, noting strong noise following signal cut-off.
Abstract: Latitudinal cut-off of manmade VLF signals in short path through ionosphere to OGO 2 satellite, noting strong noise following signal cut-off

Journal ArticleDOI
TL;DR: In this article, the cyclotron resonance interaction of a packet of finite amplitude "whistler" mode waves, travelling in the direction of the ambient magnetic field, with a collection of high energy electrons spiralling along the field is examined.

Journal ArticleDOI
01 Jan 1969
TL;DR: In this paper, the ion composition of the ionosphere is derived from two sources: noise bands with a lower frequency cutoff at the lower hybrid resonance (LHR) frequency, and ion whistlers.
Abstract: VLF observations from the Alouette satellites have provided information on the ion composition of the ionosphere. This is derived from two sources: noise bands with a lower frequency cutoff at the lower hybrid resonance (LHR) frequency, and ion whistlers. The LHR frequency depends on the harmonic mean mass of the ionic constituents. Ion whistlers provide good measurements of the relative abundances of protons and helium ions, as well as the proton density and on occasion, proton temperatures.

Journal ArticleDOI
TL;DR: In this paper, a synoptic study of the worldwide distribution and occurrence of v. l. f. electromagnetic wavefields above the ionosphere using a multi-channel receiver with a loop aerial is presented.
Abstract: The v. l. f. experiment on Ariel III is designed to make a synoptic study of the worldwide distribution and occurrence of v. l. f. electromagnetic wavefields above the ionosphere using a multi-channel receiver with a loop aerial. This report is based on a preliminary examination of data obtained during some 200 satellite revolutions. It has been found convenient to divide the observed phenomena into four main classes. ( a ) Man made transmissions . These are signals transmitted at 16 kHz from GBR (Rugby), U. K. and at 15⋅5 kHz from NWC (Australia). ( b ) Medium and low latitude emissions . These usually have a well-defined high latitude boundary—probably the plasma pause. ( c ) High latitude ‘hiss9 . This well-defined zone of broad band noise occurs at invariant latitudes, Ʌ, greater than 60° ( L = 4) and is observed on the majority of revolutions. It is probably associated with the inner zone of soft electron (few keV) precipitation located outside the trapping boundary. ( d ) Thunderstorm emissions . The sferic impulses of large signal amplitude, generated in lightning discharges, are a powerful probe for the study of D-region phenomena and of geomagnetic field-alined structure in the ionosphere and magnetosphere. The occurrence and behaviour of these phenomena are discussed in relation to the structure of the magnetosphere and to magnetic storm effects. The equatorial arch of enhanced ionization is also found to have a marked effect on the v. l. f. wavefields.

Journal ArticleDOI
TL;DR: In this article, the effects of heavy ions on the propagation of electromagnetic waves of frequency 10 Hz to 30 kHz incident at angles of 30° and 80° on the lower ionosphere were investigated.


Journal ArticleDOI
TL;DR: VLF emissions intensity and spectra variations compared with energetic electron fluxes variations during magnetosphere storm periods were compared in this article, showing that VLF emissions are more sensitive to magnetosphere storms.
Abstract: VLF emissions intensity and spectra variations compared with energetic electron fluxes variations during magnetosphere storm periods

Journal ArticleDOI
TL;DR: In this paper, the spectral distribution in the 0.3 − 3 region of the solar radiation during a flare was evaluated by means of amplitude and phase variations induced in a VLF radio link.

Journal ArticleDOI
TL;DR: In this paper, a phase radar technique is used to determine an accurate phase height of reflection for a propagation path near vertical incidence, and the analysis of these data has yielded the average phase height behavior during periods of total darkness, continuous sunlight, and day-night, night-day transition.
Abstract: The lower ionosphere above Byrd Station, Antarctica, is probed using radio waves over the frequency range 3.0 kHz to 30 kHz. A new phase radar technique is used to determine an accurate phase height of reflection for a propagation path near vertical incidence. The results of the first seven months of synoptic sounding of the polar D region are presented. The analysis of these data has yielded the average phase height behavior during periods of total darkness, continuous sunlight, and day-night, night-day transition, under both quiet and disturbed magnetic conditions. The dominant ionization production mechanism is related to energetic particle precipitation and is only slightly affected by solar ultraviolet radiation. Phase height measurements obtained during a large polar cap absorption event are also shown.

04 Mar 1969
TL;DR: In this paper, the results of these investigations have been reanalyzed in light of theoretical waveguide results to yield revisions to a vlf effective ground conductivity map of those areas developed through a correlation of geological and climatological data with conductivity.
Abstract: : Several airborne and ground-based experiments were conducted between 1959 and 1961 to investigate the propagation of very-low-frequency (vlf) radio waves over a large portion of Canada and Greenland. The results of these investigations have been reanalyzed in light of theoretical waveguide results to yield revisions to a vlf effective ground conductivity map of those areas developed through a correlation of geological and climatological data with conductivity. The experimental data confirm the theoretical attenuation rates for a daytime ionosphere with a height of 70 km and a gradient of 0.3/km for several effective ground conductivities from very high, such as seawater, down to as low as 0.00001 mho/m. There were also many indications that the theoretically determined excitation factors were substantiated by the experimental data for several values of receiving terminal foreground conductivity. A comparison of experimental propagation data with calculated values based on the theoretical model was used to modify the conductivity map. The confidence level of the original map was low in all areas where the conductivity was revised. Other propagation data, obtained over relatively long periods of time, were then used to demonstrate the accuracy of field-strength calculations based on the theoretical model and the modified conductivity map. These data also show that the daytime ionospheric gradient for the northern latitude paths investigated changes from 0.3/km around equinox to about 0.5/km in midsummer. (Author)

01 Jul 1969
TL;DR: In this paper, the authors describe a device that simulates HF atmospheric radio noise and is modeled after the available published characteristics of such noise, computer-analyzed samples, and empirical observations.
Abstract: : Generally it is not feasible, or it is too costly, to conduct performance tests of a radio-communication system under the influence of actual atmospheric radio noise because of its nonstationarity and because of the difficulty in obtaining the desired noise conditions. Accurate simulation of desired conditions solves both difficulties. The device described here simulates HF atmospheric radio noise and is modeled after the available published characteristics of such noise, computer-analyzed samples, and empirical observations. The simulation is valid and accurate for the limited samples used. The basic concept of the device is sufficiently flexible that, with adequate statistical data, the several parameters could be adjusted so that the device could simulate any atmospheric radio noise condition likely to occur form ELF to VHF. (Author)

Journal ArticleDOI
TL;DR: Long range relative precise positioning was attempted with the use of existing very low frequency radio transmitters, shipboard receivers and precision frequency standards and a computer algorithm which converts the observed time delays to precise ships position was used.
Abstract: Long range relative precise positioning was attempted with the use of existing very low frequency (VLF) radio transmitters, shipboard receivers and precision frequency standards. The VLF receivers were initially set to a calculated time delay at the known geographic location. The change in range (determined from the transmission time delays and propagation velocities) combined with known transmitter locations was used to determine an updated ships position. A computer algorithm which converts the observed time delays to precise ships position was used and is described in this paper. The analytic approach uses the Andoyer-Lambert distance formula for computing propagation distances and azimuth angles relative to the transmitter locations by an iterative method. A shipboard digital computer was used to solve the algorithm which converges on the true ships position from an assumed ships position, even with large initial position errors. Computer simulation of the navigation system and actual shipboard results are presented. ( Author )


01 Mar 1969
TL;DR: In this article, power patterns for VLF radiation (500 Hz to 30 kHz) from magnetic and electric dipole sources in a two-component lossy magnetoplasma were presented.
Abstract: : Power patterns are presented for VLF radiation (500 Hz to 30 kHz) from magnetic and electric dipole sources in a two-component lossy magnetoplasma. The patterns show that energy tends to be transported primarily along the magnetic axis of a confinement cone for higher VLF frequencies, but that the inclusion of ion motion destroys the confinement cone for extremely low frequencies. (Author)

Journal ArticleDOI
01 Jan 1969-Nature
TL;DR: In this paper, Allcock showed that Martyn's absorption theorem is valid even at low (LF 30-300 kHz) and very low (VLF 10-30 kHz) frequencies.
Abstract: MARTYN1 proved theoretically that, provided the effect of the Earth's magnetic field was neglected, the absorption of a radiowave of frequency f incident obliquely on the ionosphere at an angle of incidence i was equal to the absorption of a vertically incident wave of frequency f cos i multiplied by the factor cos i (Martyn's absorption theorem). Experimental investigations of the theorem were undertaken by Beynon2 and Allcock3, both of whom concluded that its accuracy was considerably improved if the cos i multiplying factor was omitted. Later theoretical work4 supported the omission of the cos i term. The simple ray-theory on which Martyn's theorem is based breaks down at low frequencies because conditions in the ionosphere change appreciably within the distance of one wavelength. Allcock3 demonstrated experimentally, however, that to a first approximation the theorem was valid even at low (LF 30–300 kHz) and very low (VLF 10–30 kHz) frequencies. It has since become customary to express the reflexion coefficients of LF and VLF radiowaves propagated at oblique incidence in terms of vertical incidence propagation at an equivalent vertical frequency of f cos i and to assume that the reflexion coefficient will be the same for all paths having identical values of f cos i. Furthermore, effects resulting from changes of path direction relative to the Earth's magnetic field have also been neglected and no distinction drawn between the reflexion coefficient (∥R∥) and the conversion coefficient (∥R⊥) for angles of incidence less than 50°.

Patent
07 May 1969
TL;DR: A phase-setting device for very low, low and high frequencies, comprising phase-shifters, scaling circuits, very low frequency and low frequency mixers, and a variable-frequency oscillator, securing high accuracy of phase-shift setting over a broad range of frequencies from very low to high as discussed by the authors.
Abstract: A phase-setting device for very low, low and high frequencies, comprising phase-shifters, scaling circuits, very low frequency and low frequency mixers, and a variable-frequency oscillator, securing high accuracy of phase-shift setting over a broad range of frequencies from very low to high.

01 Dec 1969
TL;DR: In this article, the variability in phase and amplitude of propagated VLF/LF radio waves is examined as a function of frequency for a variety of environmental parameters by two methods.
Abstract: : Technological development in VLF/LF engineering has progressed sufficiently so that a practical interest in the design and construction of wide-band communication systems has developed. The report demonstrates that the variability in phase and amplitude of propagated VLF/LF radio waves needs careful evaluation when wide-band modulation schemes are considered. This variability is examined as a function of frequency for a variety of environmental parameters by two methods. The first method is by an analytical study using a theoretical wave hop propagation model for establishing general concepts of conditions which may be encountered, and the second is an examination of propagation data acquired with a VLF/LF multifrequency sounder. (Author)