Showing papers on "Radio wave published in 1969"
01 Jan 1969
TL;DR: In this paper, the potential usefulness of acoustic methods for the remote probing of the lower atmosphere is reviewed, starting with a comparison of the effects of temperature, wind, and humidity fluctuations upon the refractive index of air to electromagnetic and acoustic waves.
Abstract: The potential usefulness of acoustic methods for the remote probing of the lower atmosphere is reviewed. Starting with a comparison of the effects of temperature, wind, and humidity fluctuations upon the refractive index of air to electromagnetic and acoustic waves, it is shown that the fluctuations in acoustic refractive index may be expected to be about 1000 times stronger than in the radio case. The opportunities for passive and for line-of-sight remote acoustical sensing of the troposphere offered by this relatively strong interaction are briefly identified. Since the scattered power is proportional to the square of the refractive index fluctuations, the scatter of acoustic waves may be expected to be roughly one million times stronger than for radio waves. Based on the theoretical work of Kallistratova (but including the effects of atmospheric absorption), the system parameters required for effective acoustic echo-sounding of the lower atmosphere are deduced. It is concluded that the acoustic sounding technique could be developed to monitor, to heights of at least 1500 meters, 1) the vertical profile of wind speed and direction, 2) the vertical profile of humidity, 3) the location and intensity of temperature inversions, 4) the three-dimensional spectrum of mechanical turbulence, and 5) the three-dimensional spectrum of temperature inhomogeneity (i.e., of optical refractive index fluctuation). Typical time and height resolutions for the proposed acoustic echo-sounders could be of the order 10 seconds and 10 meters; the spatial wave number explored could range from about 10-2m-1to about 400 m-1.
176 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
01 Jan 1969
TL;DR: In the decade since the International Geophysical Year, information about the ionospheric absorption of radio waves during periods of auroral and magnetic disturbance has been greatly increased by the use of the riometer technique as mentioned in this paper.
Abstract: In the decade since the International Geophysical Year, information about the ionospheric absorption of radio waves during periods of auroral and magnetic disturbance has been greatly increased by the use of the riometer technique. Such studies are important for their geophysical implications as well as in direct applications to radio propagation. The purpose of this paper is to summarize the state of knowledge of auroral radio absorption at about the end of 1968, and at the same time to give the major references through which the reader may be enabled to study any particular questions in greater depth.
124 citations
TL;DR: LF wave propagation and emission in magnetosphere, discussing steady noise and discrete emissions as mentioned in this paper, discussed steady noise in the magnetosphere and its effect on the magnetospheric magnetosphere.
Abstract: LF wave propagation and emission in magnetosphere, discussing steady noise and discrete emissions
110 citations
TL;DR: In this article, the scintillation index was found to vary as (distance)−1.6 in the range 0.1-1.5 a.u.u and the scale of the plasma irregularities was derived in the ranges 0. 1 −1.0 a.
79 citations
TL;DR: In this paper, wind speeds at heights of about 95 km have been derived from observations of the fading of LF radio waves during the past 12 yr. Systematic changes in the "steady" and "12-hourly periodic" components are described.
62 citations
TL;DR: In this paper, a study was made of type III solar radio noise bursts that appear in the recordings of the swept-frequency receivers in the Alouettes I and II satellites.
57 citations
01 Jan 1969
TL;DR: In this article, the results obtained from the background noise experiment in the Alouette satellites are summarized and the various natural emissions, most of which can reach intensity levels as high as 80 dB above receiver threshold, are identified in the recordings with reference to the characteristic frequencies of the ionosphere local to the spacecraft and described in turn.
Abstract: The principal results obtained from the background noise experiment in the Alouette satellites are summarized. The various natural emissions, most of which can reach intensity levels as high as 80 dB above receiver threshold, are identified in the recordings with reference to the characteristic frequencies of the ionosphere local to the spacecraft and are described in turn. Galactic noise is the predominant signal above f T , with some occasional solar noise contributions; emissions are described and values are presented for the galactic spectrum between 0.6 and 12 MHz. Below f T , four distinct ionospheric emissions are recognized and tentatively associated with plasma processes. They are 1) a noise band below f H which is thought to result from cyclotron emission from energetic electrons, 2) a band that occurs mainly between f H and f z S and which probably results from a spacecraft interaction with the local plasma, 3) a noise band between f z S and f T which is believed to result from transverse electrostatic oscillations, and 4) a band at frequencies above f N which probably results from longitudinal electrostatic oscillations in the ionosphere. These ionospheric emissions show an association with ionization irregularities; at times, also, overtones and intermodulation products of such emissions can be clearly recognized at frequencies above f T .
TL;DR: In this paper, the largest reflectors give a resolution of 2 to 3 min of are, close to that of the unaided human eye, and this exceeds the resolution of Michelson's stellar interferometer by more than an order of magnitude.
Abstract: Recent developments have greatly increased the angular resolution attainable in radio astronomy. The largest reflectors give a resolution of 2 to 3 min of are, close to that of the unaided human eye. Interplanetary scintillations and interferometry give 10^(-3) sec of arc and higher; this exceeds the resolution of Michelson's stellar interferometer by more than an order of magnitude, and is comparable to the highest resolution attained by the optical intensity interferometer (1).
TL;DR: In this paper, the power density spectrum of ionospheric scintillation of a radio star and satellites, at a subauroral location, has revealed the following: (1) Scintillations generally display a "pink" noise spectrum, with almost uniform spectral density at frequencies below ∼ 0.01 Hz, and decreasing spectral density in frequencies above this value, with n being typically 2.7 (i.e., a decrease of 8 db per octave).
Abstract: A study of the power density spectrum of ionospheric scintillation of a radio star and satellites, at a subauroral location, has revealed the following: (1) Scintillations generally display a ‘pink’ noise spectrum, with almost uniform spectral density at frequencies below ∼0.01 Hz, and decreasing spectral density at frequencies above this value. (2) At frequencies ƒ ≳ 0.01 Hz, the power spectrum varies as ƒ−n, with n being typically 2.7 (i.e., a decrease of 8 db per octave). (3) The width of the spectrum displays a diurnal variation such that, on the average, higher scintillation frequencies are observed at night than during the day. These results have been examined in the context of existing theories involving electrodynamic or hydromagnetic processes, in an attempt to establish the source of the ionospheric irregularities. Although many theories suggest that hydromagnetic waves are responsible for the observed irregularities, they leave the precise nature of the interaction in doubt. It is noted that the spectrum of geomagnetic micropulsations is in substantial agreement with the scintillation power spectrum, and, therefore, a theory is developed tying the two phenomena together. A model is proposed in which horizontally ducted hydromagnetic waves produce irregularities in the F region and geomagnetic micropulsations, causing both to have the same power law spectrum.
01 Jan 1969
TL;DR: In this article, the plasmas observed by top-side sounder satellites appear as persistent ringing signals at the plasma frequency and at multiples of the electron-cyclotron and upper hybrid frequencies.
Abstract: The plasma resonances observed by topside sounder satellites appear as persistent ringing signals at the plasma frequency and at multiples of the electron-cyclotron and upper hybrid frequencies. They are attributed to slow, electrostatic waves which occur near these frequencies. Explanations have progressed from invoking stationary waves or waves moving with the satellite to invoking waves which are reflected back to the satellite by the vertical electron-density gradient. In addition to the principal resonances, plasma echoes, proton-period modulation, lower frequency resonant signals, and "floating" resonances are also observed.
01 Apr 1969
TL;DR: In this article, a coherent transponder between a pair of satellites at a frequency of 5 GHz was used to record changes of 3 cm in the phase path, giving a sensitivity to changes in atmospheric density of 1:18 000.
Abstract: A pair of satellites in the same earth orbit but separated by about 60° in phase will have a radio path between them that intersects the atmosphere continuously. With a coherent transponder between satellites at a frequency of 5 GHz, changes of 3 cm in the phase path can be recorded, giving a sensitivity to changes in atmospheric density of 1:18 000. With a set of six satellites to sense density at five levels, sufficient resolution is acquired to define the vertical density profile for weather prediction equations. Three such systems in polar orbit will give the necessary world-wide resolution every 12 hours. Actual motion of the satellites due to orbit perturbations can be corrected for, giving air pressure accuracy better than 3 mbars with existing knowledge of the earth's gravity and with long term averaging of data from the satellites' own transponders. Below about 7 km, correction must be made for water vapor effects on the radio waves. Several techniques are available to extend the desired precision down to 5 km and may be able to give the necessary corrections down to 3 km.
TL;DR: In this article, the authors derived two alternative models of active region streamers in the outer solar corona, assuming that the bursts correspond to radiation near the electron plasma frequency, which led to streamer Model I in which the streamer electron temperature derived from collision damping time falls off much more rapidly than in the ‘average’ corona and the electron density is as much as 25 times the average coronal density at heights of 10 to 50 solar radii.
Abstract: Type III solar radio bursts observed from 3.0 to 0.45 MHz with the ATS-II satellite over the period April–October 1967 have been analyzed to derive two alternative models of active region streamers in the outer solar corona. Assuming that the bursts correspond to radiation near the electron plasma frequency, ‘pressure equilibrium’ arguments lead to streamer Model I in which the streamer electron temperature derived from collision damping time falls off much more rapidly than in the ‘average’ corona and the electron density is as much as 25 times the average coronal density at heights of 10 to 50 solar radii (R⊙). In Model II the streamer electron temperature is assumed to equal the average coronal temperature, giving a density enhancement which decreases from a factor of 10 close to the Sun to less than a factor of two at large distances (> 1/4 AU). When the burst frequency drift is interpreted as resulting from the outward motion of a disturbance that stimulates the radio emission, Model I gives a constant velocity of about 0.35c for the exciting disturbance as it moves to large distances, while with Model II, there is a decrease in the velocity to less than 0.2c beyond 10 R⊙.
TL;DR: Cosmic radio background noise spectrum near the north galactic pole based on Radio Astronomy Explorer satellite experiments was used in this article to estimate the radio noise near the North Galactic Pole (NGP).
Abstract: Cosmic radio background noise spectrum near north galactic pole based on Radio Astronomy Explorer satellite experiments
TL;DR: In this paper, the authors have been recording at Ahmedabad the field strengths of radio waves of 164 kHz transmitted from Tashkent, and a pronounced minimum recurred night after night in the months April to July, the local time of the minimum shifting to earlier hours as the days advanced.
Abstract: SINCE early 1960 we have been recording at Ahmedabad the field strengths of radio waves of 164 kHz transmitted from Tashkent. A pronounced minimum recurred night after night in the months April to July, the local time of the minimum shifting to earlier hours as the days advanced from April to July.
TL;DR: Pulse by pulse observations of CP 0328 have revealed very high degrees of polarization.
Abstract: Pulse by pulse observations of CP 0328 have revealed very high degrees of polarization.
TL;DR: Isotropic cosmic X-rays in the I keV-I MeV range may be due to the Compton-blackbody process acting in remote radio galaxies or quasars as mentioned in this paper.
Abstract: Isotropic cosmic X-rays in the I keV–I MeV range may be due to the Compton-blackbody process acting in remote radio galaxies or quasars. The break in the X-ray spectrum then poses a stringent condition on theories of radio source evolution and distribution.
01 Jan 1969
TL;DR: In this paper, the problem of the reflection of a plane single-frequency electromagnetic wave from a statistically rough dielectric boundary with arbitrary e is solved in the perturbation approximation.
Abstract: The problem of the reflection of a plane single-frequency electromagnetic wave from a statistically rough dielectric boundary with arbitrary e is solved in the perturbation approximation. The statistical characteristics (scattering cross section, change of polarization, and frequency spectrum) of a radar signal reflected from a rough sea surface are investigated. The model used for the surface—a small ripple superimposed on large waves—enables the perturbation theory approach to be extended to the decimeter and centimeter wave band.
TL;DR: The discovery of strong light flashes from pulsar NP 0532 is confirmed in this paper from McDonald Observatory as discussed by the authors, which is the only work that we are aware of that is related to our work.
Abstract: The discovery of strong light flashes from pulsar NP 0532 is confirmed in this paper from McDonald Observatory
TL;DR: In this article, it was shown that the noise bands observed by the British satellite Ariel III are probably generated by Cerenkov radiation from auroral electrons with energies of a few keV.
Abstract: IN recent years a number of rocket and satellite observations have been made of intense radio noise in the topside ionosphere (refs. 1–5, 12, 15 and personal communication from D. Walsh). The noise occurs in frequency bands in the neighbourhood of the plasma and gyro frequency. Data received from the British satellite Ariel III show that some of the noise bands occur only when the satellite is within the range of invariant latitude which corresponds to the auroral zones. Until recently very little has been known about how noise bands are generated. Our results show that the noise bands observed by Ariel III are probably generated by Cerenkov radiation from auroral electrons with energies of a few keV.