Radio Wave Propagation Effects Research Articles

The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components

ABSTRACT Solar radio bursts generated through the plasma emission mechanism produce radiation near the local plasma frequency (fundamental emission) and double the plasma frequency (harmonic). While the theoretical ratio of these two frequencies is close to 2, simultaneous observations give ratios ranging from 1.6 to 2, suggesting either a ratio different from 2, a delay of the fundamental emission, or both. To address this long-standing question, we conducted high-frequency, high-time resolution imaging spectroscopy of type III and type J bursts with fine structures for both the fundamental and harmonic components with LOFAR between 30 and 80 MHz. The short-lived and narrow frequency-band fine structures observed simultaneously at fundamental and harmonic frequencies give a frequency ratio of 1.66 and 1.73, similar to previous observations. However, frequency-time cross-correlations suggest a frequency ratio of 1.99 and 1.95 with a time delay between the F and H emissions of 1.00 and 1.67 s, respectively for each event. Hence, simultaneous frequency ratio measurements different from 2 are caused by the delay of the fundamental emission. Among the processes causing fundamental emission delays, anisotropic radio-wave scattering is dominant. Moreover, the levels of anisotropy and density fluctuations reproducing the delay of fundamental emissions are consistent with those required to simulate the source size and duration of fundamental emissions. Using these simulations we are able to, for the first time, provide quantitative estimates of the delay time of the fundamental emissions caused by radio-wave propagation effects at multiple frequencies, which can be used in future studies.

Machine Learning Approaches for Radio Propagation Modeling in Urban Vehicular Channels

The use of vehicular communications is anticipated to improve safety in road traffic. The traditional radio channel models that describe the effects of radio wave propagation in dynamic vehicular environments have their own limitations. In this paper, machine learning techniques are applied for radio channel modeling in urban vehicular environments. A large data set of path loss and RMS delay spread is computed using ray-tracing for a Line-of-Sight (LOS) straight road and a Non Line-of-Sight (NLOS) intersection road scenario. Fourteen input features are used to train three machine learning models for vehicular channel prediction. The models considered in this work include Multi-layer perceptron (MLP), Convolutional neural network (CNN) and Random forest (RF). The results show that RF gives better performance than MLP and CNN models in prediction of path loss and RMS delay spread in urban vehicular channels.

The Transfer Function of a Boreholed Dipole Antenna

In this paper, a semiempirical model is presented to characterize the transfer function and scattering parameters of a vertical dipole antenna in the 164–174 MHz bandwidth. The antenna is either radiating in free space or it is inserted in an air-filled borehole in a salt mine. The model uses the signal flow graph for modeling of the antenna coupling with the environment and the effects of radio wave propagation in the layered medium. Analytical results are fit to measurements performed with a vector network analyzer, and the transfer functions are obtained by applying a least mean square algorithm. Experimental data acquired in free space allow also the determination of the intrinsic parameters of the antennas, providing a stand-alone method.

Imaging spectroscopy of solar radio burst fine structures

Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, the inhomogeneous turbulent corona strongly affects the propagation of the emitted radio waves, so decoupling the intrinsic properties of the emitting source from the effects of radio wave propagation has long been a major challenge in solar physics. Here we report quantitative spatial and frequency characterization of solar radio burst fine structures observed with the Low Frequency Array, an instrument with high-time resolution that also permits imaging at scales much shorter than those corresponding to radio wave propagation in the corona. The observations demonstrate that radio wave propagation effects, and not the properties of the intrinsic emission source, dominate the observed spatial characteristics of radio burst images. These results permit more accurate estimates of source brightness temperatures, and open opportunities for quantitative study of the mechanisms that create the turbulent coronal medium through which the emitted radiation propagates.

Solar type III bursts with high‐frequency cut‐off

BackgroundSolar activity often manifests in type III bursts. Some of them can have high‐frequency cut‐off. The origin of this phenomenon is unclear until now.Materials and MethodsNew results in the study of solar bursts with high‐frequency cut‐off observed with the UTR‐2 radio telescope are presented. The bursts were associated with the emergency of a new group of solar spots behind the solar limb relative to an observer on the Earth.ResultsWe have identified the radio events with type III by analyzing its frequency drift rate, duration and flux depending on frequency. The cut‐off feature is considered in the context of specific effects of radio wave propagation between the burst sources moving behind the solar limb and the ground‐based radio instruments.ConclusionsThe role of tunnel‐like cavities with low density in the solar corona can be crucial for the emergence of solar decameter bursts with high‐frequency cut‐off.

Frequency scaling of slant‐path atmospheric attenuation in the absence of rain for millimeter‐wave links

AbstractBroadband satellite communications systems, either used for broadcast or fixed satellite services, have grown continuously in recent years. This has led to the use of higher frequency bands, from the Ku (14/11 GHz) to the Ka band (30/20 GHz) in the last decade, and with the expectation of using the Q/V band (50/40 GHz) and even the W band (75–110 GHz) in the future. As frequency increases, radio wave propagation effects in the slant‐path within the troposphere are becoming more and more relevant. The objective of this research is the proposal of frequency scaling approximations for the total attenuation in the absence of rain, a condition that occurs during the highest percentages of time, usually more than 95% in temperate climates. There is a strong relationship between total attenuation at different frequencies, as it arises from the same physical phenomena, namely, the presence of oxygen, water vapor, and clouds in the slant path. This strong relationship allows frequency scaling estimations to be proposed. In particular, polynomials for instantaneous frequency scaling of total attenuation under these conditions have been calculated for a set of frequencies in the range 10–100 GHz, based on atmospheric profiles of 60 sites from all over the world and physical models of attenuation. Global polynomials are provided for the 72 combinations of nine significant frequencies, which can be used to estimate attenuation at a frequency band from its known value at a different one. Refined expressions have also been calculated for different climatic zones, providing more precise estimations.

DGPS 전파 신호의 안정도 측정 및 분석

The stability of DGPS signal in the DGPS service area was measured and the service availability according to the receiving signal strength was analyzed in this paper. Based on the effects of radio wave propagation in the seasons of winter and summer, daytime and night, the method to provide the DGPS service coverage was presented in this paper. The signal`s strength of DGPS radio wave were measured at a constant distance from the DGPS reference station during a constant period. The propagation of DGPS radio wave is affected by status of ground conductivity, so the DGPS service area is dependant on the ground conductivity. To provide the stable service coverage, it is necessary to apply the adaptive power control for receiving signal`s variations and the antenna design for alleviation of high elevation`s radiation.

A Simulation System of Radio Propagation Effect Evaluation Based on GIS

Construction of wave propagation effects assessment simulation system based on GIS, for enhancing the capabilities of our military radio environment awareness, forecasting, warning and assessment of the effect is significant.In this paper, the original geographic data and radio wave propagation data will be unified as vector and raster data into GIS system structure based on ArcObjects components, combined with the development of visual language Visual C++ 6.0, designed and constructed to assess the effect of radio wave propagation simulation system. designed and built a radio wave propagation effects assessment simulation system. The system has data management, scene visualization, effects assessment, graphics output function modules, Achieved wave propagation effects assessment simulation and visualization presentation.

Radio wave propagation effects produced by chemical releases in the ionosphere

As an effective means to actively modify the ionosphere, chemical release can produce artificial ionospheric holes as a consequence of ionization depletion, which can greatly impact on radio wave propagation. In this paper, on the basis of the pre-study results on ionospheric disturbances produced by some representative chemical releases, the radio waves propagation effects of ionospheric holes that are produced by two different release species, water (H2O) and sulfur hexafluoride (SF6), had been investigated and simulated by the three-dimensional (3-D) numerical ray tracing. The results show that ➀ the appearance of various artificial ionospheric holes can lead to certain decrease of critical frequency in the ionosphere, and ➁ when the wave frequency exceeds the critical frequency, the rays should be multiple reflections or penetrate through the ionospheric hole and focus afterwards with the focus altitude elevated for higher frequencies. This work may provide the necessary theoretical support for chemical release experiments and the evaluation of radio wave propagation effects.

Eikonal acceleration technique for studying of the Earth and planetary atmospheres by radio occultation method

[1] Lately introduced a phase (eikonal) acceleration technique extends an applicable domain of radio occultation (RO) method and can be applied for identification of the plasma layers in the lower ionosphere. This technique can also convert the eikonal excess or Doppler frequency changes measured in RO experiments into the refractive attenuation variations. From these derived refractive attenuation and amplitude data one can estimate the integral absorption of radio waves. This is important for study of the radio wave propagation effects in the atmospheric telecommunication links and for remote sensing of the atmosphere and ionosphere. The advantages of the eikonal acceleration technique are validated by analyzing the RO data from the Challenging Minisatellite Payload (CHAMP) and Venus missions.

Atmospheric Radiowave Propagation Effects on Spatial Resolution of Spaceborne Synthetic Aperture Radar

摘要: 利用合成孔径原理和大气折射理论推导了大气层给SAR方位向分辨率带来的误差公式,针对不同时间、地点、高低年的电离层电子浓度和低层大气折射率剖面,对不同频段进行了计算,并对计算结果进行了分析讨论.得出了大气层中星载SAR的方位向分辨率误差为毫米量级,其绝对值随频率增高而减小的结论. 关键词: SAR / 方位向分辨率 / 误差

Ionosphere plasma holes-modeling and diagnostic

The influence of ionosphere plasma holes on HF radio wave propagation in approximation of geometrical optics is studied. The results of HF radio wave propagation modeling on routes crossing ionosphere holes are presented. The natural and modeling ionosphere sections are used (we use experimental radiotomography sections on routes: Moscow-Arkhangelsk, Moscow-Murmansk (Russia) and Block Iland-Rabiwhol (USA)). It is shown that characteristics of HF radiowave trajectory (in coordinate: height-latitude) depend on geometrical sizes of hole and the direction, point, angle and frequencies of sounding. It is shown that the asymmetry of electron density distribution results in qualitative and quantitative distinctions of waves trajectories characteristics in dependencies on direction propagation. The characteristic modes of HF radio wave propagation through hole are emphasized — one hop, captured by channel E-F, captured by hole, trapezifrom and so on. The higher interest presents the family of trajectories captured by hole. On estimations, the longest time-delay for different conditions makes up to 23 ms (or range up to 7000 km!). It is possible to say, that the hole in ionosphere can be the trap of HF radiowave. It is discussed conditions of capture and keeping of radio wave by ionospheric hole. The fact, that holes in top ionosphere are long-living and large-scale formations, indicates that disregard of radiowave propagation effects, connected with holes, will result in data distortion or misunderstanding of ionosphere monitoring and control by radiosounding in HF radiowave range.

Multiple reflections of radio waves in a corridor

New results of radio wave propagation effects in indoor environments for mobile and personal communications are presented. Complex impulse responses and their spatial variations when shifting the mobile antenna were measured with a very high time dispersion resolution. Measured results are compared to results derived from model calculations, using the geometrical description of the environment. The high resolution of the measurement system allows via the scattering function a very detailed analysis of the wave propagation process. This is demonstrated for propagation in a regular corridor (simple cubic geometries). The influence of metallic scatterers in producing multiple reflections like in a large waveguide is shown. >

LF radiowave propagation effects of meteoric ionization

Ionization deposited by large meteors has been recently proposed as the agent directly responsible for apparent LF radiowave absorption events. A quantitative examination demonstrates that the proposal is untenable.

Heliographic longitude distribution of the flares associated with type III bursts observed at kilometric wavelengths

We have grouped observed type III solar bursts according to the discrete frequencies of observation in the kilometric wavelength range. For each group we have obtained the bursts' frequency of occurrence as a function of the heliographic longitude of the associated optical flares. We found that flares occurring east of a certain cutoff longitude do not produce bursts observable near the earth below a given frequency. The cutoff on the west is determined by observational limitation for flares beyond the limb. The mean longitude and the extreme eastern end of the longitude distribution both shift to the west as the radio frequency decreases. We interpret these findings in terms of radio wave propagation effects and curved trajectories of the bursts' exciter particles.

Direct Observations of Low-energy Electrons in the Disturbed Ionospheric E-region

DIFFERENTIAL spectra of electrons 20–3,000 eV in energy have been directly measured in the ionosphere for the first time. The spectrometer used an open electron multiplier as its detector, counting individual electrons. It was carried in Black Brant II rockets launched in 1963 at Churchill, Manitoba, in the presence of so-called auroral absorption (of very-high-frequency cosmic radio noise). Such absorption events usually last from a few minutes to about an hour, with rapid fluctuations, and occur in or near the auroral zone. Electrons of energy < 100 keV, precipitated into the ionosphere by processes not understood but closely related to magnetic activity, are considered to be the main cause of these events. A great deal of information exists on the upper part of this energy range, but below 10 keV there is very little1,2. Our experiment covered a large part of this unknown region. In order to provide a more complete spectrum, measurements on electrons above 10 keV were made aboard the same rockets by instruments from the National Research Council of Canada. In addition, experiments measuring electron density and radio-wave propagation effects were carried, the results from which will be discussed in future publications.

Effects of radio wave propagation through mid-latitude 6300 A auroral arcs

Effects of radio wave propagation through mid-latitude 6300 A auroral arcs