Showing papers on "Radio wave published in 1972"

High frequency induced enhancements of the incoherent scatter spectrum at Arecibo

Abstract: Observations are reported of enhancements of the incoherent scatter spectrum excited by strong high frequency (HF) radio waves. A number of enhancement characteristics, observed during an ionospheric heating experiment in January at Arecibo, are described. The enhancement spectrum includes: a strong narrow line displaced below the HF (5.62 MHz) by the frequency of the ion acoustic waves fi in the plasma (about 4 kHz); a broader line (about 30-kc width) and other weak lines near the HF; and a line near fi. Enhancements above thermal levels range above a factor of 104 and may be taken as verification of the HF excitation of parametric instabilities in the ionosphere. Significant time variations over scales of tens of µsec through hours were seen. Upshifted and downshifted enhanced plasma lines display asymmetries in intensity, width, power dependence, and decay rates (of the order of msec). The O-mode (but not the X-mode) excitation of these enhancements is of significance to heating experiments.

Radio Tracking of Solar Energetic Particles through Interplanetary Space.

Abstract: Energetic particles ejected from the sun generate radio waves as they travel out through the interplanetary medium Satellite observations of this emission at long radio wavelengths provide a means of investigating properties of the interplanetary medium, including the gross magnetic field configuration over distances of 1 astronomical unit Results of such observations are illustrated

Radio echo sounding: absorption and scattering by water inclusion and ice lenses

Abstract: The absorption of radio waves propagating through naturally occurring waters varies greatly with the electrical conductivity. Glacier melt water is very transparent and the attenuation by melt water layers is due to reflexion of power, whereas the attenuation of sea-water layers is due to absorption. The attenuation of soaked firn is usually prohibitive if the liquid is brine but it should not be a serious obstacle to radio echo strength if the liquid is rain-water or melt water. However, the magnitude of the scattered power can become greater than that from continuous (bedrock) reflectors if the size of the irregularities in the medium is large (approaching the radio wavelength in ice). Echo power formulae show that ice lenses may have the most serious effect and that low radio frequencies will be necessary to combat this.

Diffraction of Radio Waves Around the Earth's Surface

Abstract: : ;Contents: Statement of the problem and its solution in series form; Summation formula; Calculation of the Hertz function for the illuminated regions; Asymptotic expressions for the Hankel function; Expression of the Hertz function applicable to the twilight regions(penumbrae); Study of the expression for the Hertz function. Summary of results.

Detection of several new interstellar molecules.

Abstract: We have detected radio emission from several new interstellar molecules and the preliminary results of our observations will be discussed. These observations were made in April and May, 1971, with the 36-foot radio telescope of the National Radio Astronomy Observatory at wavelengths of 3 mm and 1.4 cm. The radiometer used for the 3 mm observations was constructed by the National Radio Astronomy Observatory with a local-oscillator system developed by S. Weinreb of the NRAO in conjunction with A. A. Penzias, R. W. Wilson, K. B. Jefferts and C. A. Burrus of the Bell Telephone Laboratories. This receiver could be used to observe spectral lines between 85 and 95 GHz with a single-sideband noise temperature which was nominally 4,000'K. A parametric amplifier, inserted between the antenna feed and the 1.4 cm mixer radiometer, permitted a greatly improved system noise temperature of approximately 600'K for the 1.4 cm observations. This receiver system was designed and developed at the National Radio Astronomy Observatory under the direction of J. Edrich, who subsequently collaborated with us in the centimeter wavelength observations which are reported herein. A small on-line computer was adapted to the 36 ft telescope by C. Moore of the NRAO Computer Division and was utilized successfully to process spectral line data from both sets of observations. The antenna temperatures for both sets of observations were measured with respect to a calibrated noise tube; additional checks were made by means of Jupiter observations. Unexplained variations in the system temperature of the 3 mm radiometer caused some uncertainty in the antenna temperatures which we are reporting for the mm wavelength observations, but the receiver used for the 1.4 cm observations remained relatively stable. At 3 mm the 36 ft telescope has a nominal half-power beam width of 70 arc sec; this increases to approximately 5 arc min at 1.4 cm. Solar heating causes broadening of the main beam, but the observations reported herein were made al night and, accordingly, were only slightly affected by small changes in the nocturnal ambient temperature. Two filter bank spectrometers were used for these observations: the wider utilized forty filters spaced 1 MHz apart; the other one consisted of fifty filters spaced 250 kHz apart. We have identified the new interstellar molecules on the basis of pure rotational transitions as isocyanic acid (HNCO) , methylacetylene (CH&zH), and hydrogen isocyanide (HNC) . It must be recognized that the positive identification of a new molecular species requires the detection of more than one spectral line. This requirement can be satisfied for the above molecules in the following ways: ( 1 ) Detection of other rotational transitions of the same molecular isotope. (2) Resolution and identification of hyperfine structure or some other unique feature of a given rotational transition. (3) Detection of the frequency-shifted rotational transition of a less common molecular isotope.

A satellite survey of vector electric fields in the ionosphere at frequencies of 10 to 500 hertz: 3. Low‐frequency equatorial emissions and their relationship to ionospheric turbulence

Abstract: Occasional observations of intense low-frequency electric field fluctuations have been made near the magnetic equator by the vector ac electric field experiment performed on the OV1-17 satellite, which was in a circular polar orbit at an altitude of about 400 km. The observed fluctuations are correlated with spread F at an equatorial ground station located near the projection of the vehicle trajectory onto the surface of the earth. This correlation suggests that the ionospheric electric field turbulence is related to the modification of the propagation of radio waves and that this relationship results in scattering of the radio signals from irregularities of the medium. The polarization, intensity, and spectral characteristics of the signal are similar to the high-latitude low-frequency electric fields that were detected on every orbit of OV1-17 and that were described in paper 1 of this series. This similarity suggests that the instability responsible for the turbulence is the same in two regions.

Excitation of Parametric Instabilities by Radio Waves in the Ionosphere

Abstract: The excitation of parametric instabilities by radio waves in a magnetoplasma is discussed. A uniform medium is assumed and linear approximations are used. Excitation by a pump wave of ordinary polarization is hardly affected by the magnetic field. Low or zero frequency ion waves and high frequency Langmuir waves are excited simultaneously. For an extraordinary pump wave, the excited high frequency electrostatic waves are in the Bernstein mode. The threshold is slightly higher and excitation can occur only within certain 'allowed' frequency bands. A new type of parametric instability in which the excited waves are electromagnetic in nature and which is more strongly affected by the inhomogeneous nature of the medium is discussed qualitatively.

The Structure of Sporadic E From a Radio Experiment

Abstract: An ionosonde has been used to measure the ordinary and extraordinary critical and blanketing frequencies separately. While the results support the idea that transparent sporadic-E reflections occur from small volumes within the E region, it is likely that the plasma density even in these volumes is often less than that required to cause total reflection. The structure of sporadic E is probably as follows: The peak plasma frequency varies by roughly equal amounts above and below a mean value often by a megahertz or so, within a few kilometers. Some intense blobs cause total reflection; other small volumes of increased plasma frequency strongly scatter radio waves of somewhat greater frequency.

Glacier Movement measured with a Radio Echo Technique

Abstract: IN the radio echo sounding method for measuring the thickness of polar ice masses, the sounder transmits regular pulses each containing several cycles of VHF radio waves into the ice. Usually the glacier bed is rough so the echo is a distorted version of the transmitted pulse: it is lengthened and the amplitude and phase of the carrier wave vary within its length (Fig. 1). The echoes also vary rapidly with horizontal displacement of the radio echo sounder1, and this variation is known as the spatial fading pattern.

Simultaneous radio communication system between two stations

Abstract: A simultaneous radio communication system comprising first and second radio stations adapted to transmit first and second radio waves of the same radio channel and receive the transmitted second and first radio waves, in which the first and second radio waves are interrupted waves interrupted in opposite phases at the same period; the on-state periods of the transmitted first radio waves include time compressed third information of first information to be transmitted; the on-state periods of the transmitted second radio waves include time compressed fourth information of second information to be transmitted; and the first and second radio stations have means for time expansion of the time compressed fourth and third information from the second and first transmitted radio waves to obtain sixth and fifth information corresponding to the second and first information respectively.

Propagation and application of waves in the ionosphere

Abstract: This review deals with the propagation of waves, especially radio waves in the ionosphere. In the macroscopic electromagnetic theory, the mathematical structure of wave propagation problems depends entirely on the properties of the dielectric operator in a magnetically nonpermeable medium. These properties can be deduced from general discussions of symmetry and considerations of physical principles. When the medium is specifically the ionosphere, various physical phenomena may occur. Because of a large number of parameters, it is desirable to define a parameter space. A point in the parameter space corresponds to a specific plasma. The parameter space is subdivided into regions whose boundaries correspond to conditions of resonance and cutoff. As the point crosses these boundaries, the refractive index surface transforms continuously.

ELF communication system design

Abstract: Radio waves of frequency below about 1 kHz propagate around the earth-ionosphere cavity with very little attenuation. These waves also can propagate useful distances down into the ocean. They are attractive therefore, for providing long-range communication to submarines from a single site. By considering the various components of the communication channel in turn, the paper develops the design principles for such a system. Significant features are the use of insulated horizontal dipoles, grounded at each end, as the antennas, an optimum operating frequency below 150 Hz, non-linear processing in the receiver to reduce the effective atmospheric noise, and the large size but sparse installation density of the transmitting antenna.

Variability of plasma‐line enhancement in ionospheric modification experiments

Abstract: A simple explanation for the variations of plasma-line intensity is suggested. The explanation is based on the fact that the plasma waves responsible for scattering the radar waves occur over a very limited range of heights. The explanation further makes use of the fact that the position of these height ranges of generation depends primarily on the gradient of the number density and to a lesser extent on the temperature and the orientation of the diagnostic radar beam.

Faraday rotation of linearly polarized radio waves from the Crab Nebula by the solar corona

Abstract: Position angles of linearly polarized radio waves from the Crab Nebula (Tau A) were measured at wavelength lambda = 7.2 cm, in the middle of June 1971, at which time the source was occulted by the outer solar corona. The observed variation in the rotation measure suggests that there exist local structures in the magnetic field and electron density of the corona. The local structures have two typical scale lengths of the order of 0.1 and 1 R/sub sub solar /, respectively, at a distance of 5 to 10 R/sub sub solar / from the Sun. The field strength and electron density in the local structures are larger than the averaged values by a factor of 15 for the structures of scale length 0.1 R/ sup sub solar / and 4 for those of scale length 1 R/ sub solar /. Observed values of the electron density and scale length of the local structures are the same, in order of magnitude, as those for coronal streamers. The direction of the magnetic field reverses in the large scale local structure, which is identified with a radial extension of a helment streamer. (auth)

Amplitude Probability Distribution of Radio Waves Reflected From Traveling Ionospheric Disturbances

Abstract: In this paper, the amplitude distributions of the reflected radio waves, from various portions of the traveling ionospheric disturbances (TID) superimposed on small-scale irregularities, have been studied with the help of simultaneous records of amplitude and phase patterns of vertically reflected echoes. Amplitude distributions of reflected waves, related to different small portions of TID are found to exhibit different types of well-known distributions, like Rayleigh, Rice, and displaced Gaussian, while resultant distributions corresponding to two successive small portions of the TID may have different shapes, including the familiar M shape reported by many workers. Further, in some events, even three-peaked amplitude distributions are observed depending upon the ratio of steady component to random component present in the received echo and the nature of the reflecting surface.

Mode coupling in partial reflections from the ionosphere at vertical incidence.

Abstract: The effect of mode coupling has been calculated for radio waves partially reflected from the lower ionosphere at vertical incidence. Calculations were made for parameters appropriate to the partial reflection experiments (Belrose, 1970). The four reflection coefficients (two direct and two coupled) are calculated for a plane discontinuity using a matrix perturbation analysis. The ratios of coupled to direct reflection coefficients are calculated for a general one-dimensional reflecting layer using the coupled equations of Clemmow and Heading (1954). At the highest electron density considered, 10,000 per cu cm, about 10% of the reflected extraordinary wave amplitude might be due to coupling from the incident ordinary wave. The effect is smaller at lower electron density.

Radio navigation system

Abstract: The radio navigation system provides simple instrumentation for transmitting omnidirectional radio waves from a reference location and for determining the azimuth and elevation angles of arrival of the transmitted waves at a remote receiver An array of paired receiver antennas is employed for the measurement of differences in time of arrival of the transmitted waves at the paired antennas and these values are manipulated by a simple analog computer to yield the desired azimuth and elevation data

Anomalous absorption of radio waves by electrojet irregularities

Abstract: The enhanced absorption of radio waves (with a frequency close to the upper hybrid frequency) in the equatorial electrojet by resonant coupling to electrojet irregularities and damped upper hybrid modes is investigated. It is found that, under normal ionospheric conditions, the absorption coefficient for such radio waves may be increased by a factor of as large as 100.