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Radio waves are significant for operating in an underground tunnel or a cave, such as two-way radio systems or emergency communication during rescue operations. Most applications used in the tunnels require wired connections because of the high attenuation of the wireless propagation. In particular, the attenuation in caves is higher than in tunnels because of the non-uniform nature of the walls. Therefore, this paper presents a study of the radio wave propagation within a cave. The experiment covers the low-frequency (LF) to ultra-high frequency (UHF) bands that aim to analyze the attenuation and behavior of waves in caves. Study results show that the low frequency and medium frequency (MF) bands can penetrate cave walls due to the deeper skin depth. At the same time, higher frequencies perform well in line-of-sight (LOS) propagation over short distances, albeit encountering significant attenuation in non-uniform cave environments. The skin depth condition obtained in the propagation result led to the Through-the-Earth (TTE) experiment by making two hand-made transceivers in the beginning band of MF at 350 kHz for transmitting and receiving waves between the mountain surface and the cave passage directly through the rock layer. The results of the TTE experiment show that the transceivers can transmit to 571 meters with a received power of -85.0 dBm before encountering an obstacle that makes it impossible to continue. Finally, the results are significant for developing the application of radio frequency within caves or tunnels and improving the application of the TTE technique with more versatility and efficiency. [ABSTRACT FROM AUTHOR]

In this paper, the propagation of electromagnetic rays in a tropospheric waveguide and spatial processing using digital antenna arrays are studied. The beam traveling through the layers of the atmosphere depends on the refractive index and its vertical change. In this regard, conditions may arise when radio rays propagate in a waveguide manner at low altitudes. In this case, attenuation takes place, and the effect of multipath fading may also occur, when several rays reflected from different layers of the troposphere and with various spatial coordinates in elevation arrive at the receiver. It is proposed to apply digital antenna arrays to increase the range and reliability of radio communication through the tropospheric waveguide. Parabolic equations are utilized to estimate the path loses of radio waves of the centimeter wavelength. A ray-tracing algorithm via a tropospheric waveguide is used to estimate the mutual phases in the aperture of the receiving array. Bit error rate curves were obtained depending on the geometry of the antenna arrays after the signal passed through the tropospheric waveguide. [ABSTRACT FROM AUTHOR]

One of the major challenges in designing a wireless indoor–outdoor communication network operating in tunnels and long corridors is to identify the optimal location of the outside station for attaining a proper coverage. It is required to formulate a combined model, describing the propagation along the tunnel and the resulting diffracted outdoor pattern from its exit. An integrated model enables estimations of the radiation patterns at the rectangular tunnel exit, as well as in the free space outside of the tunnel. The tunnel propagation model is based on a ray-tracing image model, while the free-space diffraction model is based on applying the far-field Fraunhofer diffraction equation. The model predictions of sensing the radiation intensity at the tunnel end and at a plane located at a distance ahead were compared with experimental data obtained using a down-scaled tunnel model and shorter radiation wavelength correspondingly. This down-scaling enabled detailed measurements of the radiation patterns at the tunnel exit and at the far field. The experimental measurements for the scaled tunnel case fit the theoretical model predictions. The presented model accurately described the multi-path effects emerging from inside the tunnel and the resulting outdoor diffracted pattern at a distance from the tunnel exit. [ABSTRACT FROM AUTHOR]

Large‐scale ionospheric gradients associated with the solar terminator can deflect high frequency (HF) radio waves to off‐great circle paths during the morning and evening, negatively impacting technologies reliant on HF radio wave propagation. For example, geolocation algorithms used by scientific and military over‐the‐horizon radars (OTHRs) generally assume on‐great circle propagation, and thus lateral deviations from the great‐circle path can lead to positioning errors. In this study, radio wave propagation is simulated via 3D numerical ray traces though an empirical, high‐latitude model ionosphere initialized for a variety of times of the day and year to explore and quantify high‐latitude off‐great circle propagation associated with the solar terminator. Analysis of these simulations show large scale east‐west ionospheric gradients due to the solar terminator can cause lateral deviations in north‐directed propagation paths exceeding 20° at sunrise and sunset depending on radio wave frequency, though the largest portion of received signal power tends to experience maximum deflections of 5°. An exploration of the dependence of propagation direction on deflection shows that propagation paths parallel to the solar terminator tend to experience the largest deflections. Since the solar terminator at high latitudes is at an angle with respect to north in the winter and summer, propagation paths oriented west or east of north can experience larger deflections than north oriented paths at sunrise and sunset during these times of year. Impacts of these diurnal deflections on the operation of OTHR and scientific radar are discussed, as well as possible strategies for mitigating them. Plain Language Summary: High frequency (HF) radio waves are able to travel long distances by bouncing between the ionosphere (an upper layer of the Earth's atmosphere) and the ground. HF radio waves transmitted north can have their paths deflected east or west by changes in the ionosphere that happen at sunrise and sunset. In this paper, simulations of radio waves are used to explore how large these deflections can be and how they change over the course of the day and year. It is found that north pointing radio signals at certain frequencies can be deflected by more than 20° at sunrise and sunset. These simulations are also used to explore how radio waves transmitted in different directions are deflected at sunrise and sunset. It is found that radio waves transmitted along the dividing line between day and night tend to experience the largest deflections. The Earth is tilted with respect to its rotation, meaning this dividing line is not always aligned with North. The deviation from north is largest in the winter and summer. This means that radio waves transmitted west or east of north at these times of year can experience larger deflections than northward transmissions. Key Points: The lateral deflection of high frequency radio waves caused by the solar terminator is investigated with ray tracing simulationsNorth‐south propagation paths can experience significant (>20°) deflections in the morning and eveningEast‐west paths can also see significant deflections at high latitudes, at times when the solar terminator is also oriented east‐west [ABSTRACT FROM AUTHOR]

The Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 monostatic high‐frequency (HF, 8–20 MHz) radars to study dynamic processes in the ionosphere. SuperDARN provides maps of global‐scale ionospheric plasma drift circulation from the mid‐latitudes to the poles. The conventional SuperDARN radars consecutively scan through 16 beam directions with a lower limit of 1 minute to sample the entire field of view. In this work, we use the advanced capabilities of the recently developed Borealis digital SuperDARN radar system. Combining a wide transmission beam with multiple narrow reception beams allows us to sample all conventional beam directions simultaneously and to speed up scanning of the entire field‐of‐view by up to 16 times without noticeable deterioration of the data quality. The wide‐beam emission also enabled the implementation of multistatic operations, where ionospheric scatter signals from one radar are received by other radars with overlapping viewing areas. These novel operations required the development of a new model to determine the geographic location of the source of the multistatic radar echoes. Our preliminary studies showed that, in comparison with the conventional monostatic operations, the multistatic operations provide a significant increase in geographic coverage, in some cases nearly doubling it. The multistatic data also provide additional velocity vector components, increasing the likelihood of reconstructing full plasma drift velocity vectors. The developed operational modes can be readily implemented at other fully digital SuperDARN radars. Plain Language Summary: The Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 high‐frequency (HF, 8–20 MHz) radars that observe the ionized part of the Earth's atmosphere to study Space Weather phenomena, like magnetic storms and the aurora. Each SuperDARN radar transmits a radio wave at a particular frequency and receives the returns scattering from ionized structures. The returns are analyzed to extract information about processes in near‐Earth space. Conventionally, these radars scan 16 azimuthal directions consecutively, dwelling for 3.5 s in each direction, which restricts a scan of the field‐of‐view to 1 minute. In this work, we use a recently developed digital SuperDARN radar system called Borealis to shorten the scan duration by an order of magnitude by illuminating the whole field of view with a broad transmitter beam and receiving radar returns from all 16 directions simultaneously using narrow receiver beams. We also implemented a technique to receive signals sent from one radar by other radars with overlapping viewing areas. This provides a significant increase (nearly doubles) the geographic area of coverage, compared with using the same radar for both transmission and reception. Key Points: We developed wide‐beam transmission to probe an entire Super Dual Auroral Radar Network (SuperDARN) field of view simultaneously and to enable bistatic operationsNew multistatic operation of SuperDARN radars provides additional measured velocity vector componentsNew wide‐beam and multistatic operations significantly improve temporal resolution and spatial coverage by SuperDARN [ABSTRACT FROM AUTHOR]

High latitude ionospheric density structures such as polar cap patches and arcs are capable of deflecting high frequency (HF) radio waves to off‐great circle paths, and are likely detrimental to technologies dependent on HF radio propagation. In this study, nearly 2.5 years of 4.6–14.4 MHz data from a multi‐frequency HF radio link between Qaanaaq, Greenland and Alert, Canada are used to investigate high‐latitude off‐great circle propagation in the polar cap. After an example of HF radio propagation affected by polar cap patches is shown in detail, a statistical analysis of the occurrence and impacts of off‐great circle deflections in the polar cap is presented. Off‐great circle propagation is shown to be increasingly common with increasing frequency up to 11.1 MHz, such that averaged over 1 year, received 11.1 MHz signals experienced deflections >30° from the great circle direction 65.6% of the time. The occurrence of these deflections across the year is shown to be at a maximum in the winter, while occurrence across the day varies with season. Trends across both time of day and time of year for 11.1 and 14.4 MHz deflections are consistent with polar cap patch occurrence trends. Off‐great circle deflections are shown to be associated with increased time‐of‐flights, a larger range of positive and negative Doppler shifts, increased Doppler spreads, and lower signal‐to‐noise ratios. These results are discussed in the context of ionospheric phenomena in the polar cap, and implications for over‐the‐horizon radars operating at high latitudes. Plain Language Summary: High frequency (HF) radio waves can travel long distances by bouncing between the ground and the ionosphere; an upper layer of the Earth's atmosphere, allowing them to be used for communications and surveillance in remote locations. However, strong space weather can change the paths these radio waves take, causing problems for HF radio technologies. In this paper, radio transmissions sent between Qaanaaq, Greenland and Alert, Canada are studied in order to better understand how often HF radio waves are deflected by space weather at high latitudes, and what effect these deflections have on the signals themselves. After a brief example of what space weather deflections look like, transmissions sent over a whole year are studied to determine how deflections depend on radio frequency, time of day, and time of year. Then, the effects these deflections have on other signal properties is studied. It is found that deflections are very common at high latitudes, especially in the winter. Deflections tend to increase the travel time of signals, change their frequency, and reduce their signal strength. These results are shown to be connected to polar cap patches and arcs; which are common space weather phenomena near the poles. Key Points: Off‐great circle propagation occurring in the polar cap is studied using years of data from an HF radio link in the polar capLarge (greater than 30°) deflections from the great circle are shown to be very common, especially in the winterThese deflections are shown to affect HF radio signals in ways that are consistent with interactions with polar cap patches and arcs [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for extracting the structure of an indoor environment using radar. When using the radar in an indoor environment, ghost targets are observed through the multipath propagation of radio waves. The presence of these ghost targets obstructs accurate mapping in the indoor environment, consequently hindering the extraction of the indoor environment. Therefore, we propose a deep learning-based method that uses image-to-image translation to extract the structure of the indoor environment by removing ghost targets from the indoor environment map. In this paper, the proposed method employs a conditional generative adversarial network (CGAN), which includes a U-Net-based generator and a patch-generative adversarial network-based discriminator. By repeating the process of determining whether the structure of the generated indoor environment is real or fake, CGAN ultimately returns a structure similar to the real environment. First, we generate a map of the indoor environment using radar, which includes ghost targets. Next, the structure of the indoor environment is extracted from the map using the proposed method. Then, we compare the proposed method, which is based on the structural similarity index and structural content, with the k-nearest neighbors algorithm, Hough transform, and density-based spatial clustering of applications with noise-based environment extraction method. When comparing the methods, our proposed method offers the advantage of extracting a more accurate environment without requiring parameter adjustments, even when the environment is changed. [ABSTRACT FROM AUTHOR]

Vertical radio refractivity gradients are essential for monitoring propagation conditions when designing and planning terrestrial radio links for communications in the lower atmosphere. Average data gathered from meteorological factors such as temperature, pressure, and relative humidity was used from 1980 to 2020 n this study. This study focuses on the vertical gradient of radio refractivity within the lower atmospheric layer, investigating its influence on factors like signal propagation, route clearance, and line-of-sight communication. The analysis encompasses three cities - Abuja, Makurdi, and Jos. In Figure 2 monthly average changes in the refractivity gradient are presented for Abuja. In addition, the seasonal radio refractivity gradient shows mean values of -110.000N/km for Abuja which shows that the refractivity condition is Super-Refraction, -77.553N/km for Jos which shows that the refractivity condition is Normal-Refraction and - 97.209N/km for Makurdi which shows that the refractivity condition is Normal-Refraction respectively. Higher gradient values, G1, G2, and G3 were observed during the dry season (December-February) which could be attributed to dry air and steeper refractivity gradients. In contrast, lower gradient values were observed during the wet season (June-October) due to increased atmospheric moisture. Similarly, measured vertical radio refractivity gradient data, G1 N/km, G2 N/km, and G3 N/km for Jos displayed consistent fluctuations throughout the year. Similarly, measured vertical radio refractivity gradient data, G1 N/km, G2 N/km, and G3 N/km for Jos displayed consistent fluctuations throughout the year. Notably, wetter months exhibit higher refractivity gradient values, while drier months show lower values. G2 consistently records the highest gradient values, and despite varying magnitudes, the trends remain consistent. Finally, measured vertical radio refractivity gradient data, G1 N/km, G2 N/km, and G3 N/km for Makurdi indicate distinct fluctuations with the most negative values observed in November and December. The Dry Season witnesses relatively lower gradient values, while the Transition and Wet Seasons experience rising values, influenced by atmospheric shifts. The Higher negative values during the wet season suggest pronounced variations in the refractive index, affecting radio wave propagation. These findings emphasize the significance of refractivity gradient variations and their implications for radio wave behaviour particularly during different seasons. [ABSTRACT FROM AUTHOR]

The random amplitude and phase fluctuations observed in trans‐ionospheric radio signals are caused by the presence of electron density irregularities in the ionosphere. Ground‐based measurements of radio wave signals provide information about the medium through which these signals propagate. The Canadian High Arctic Ionospheric Network (CHAIN) Global Position System (GPS) receivers record radio signals emitted by the GPS satellites, enabling the study of their spectral characteristics. This study presents examples of phase spectra with two power‐law components. These components exhibit steeper spectral slopes at higher frequencies and shallower ones at lower frequencies. To be more specific, we conducted a spectral characterization of sixty one (61) events recorded by the CHAIN Churchill GPS receiver, which is located in the auroral oval. When fluctuations above the background level are only observed in the phase, the spectra tend to be systematically steeper. Conversely, the power increase in higher frequency fluctuations accompanying amplitude scintillation tends to result in shallower spectra. A basic yet powerful model of radio wave propagation through a turbulent ionosphere, characterized by a power law electron density spectrum, can help to explain the two power laws observed in the scintillation events presented in this study by identifying the role played by small‐scale ionospheric irregularities in diffraction. Plain Language Summary: This study discusses the impact electron density irregularities in the ionosphere have on radio wave propagation. Ground‐based measurements of Global Navigation Satellite System signals provide insights into their spectral characteristics. The study presents examples of phase spectra with two power‐law components, showing steeper slopes at higher frequencies and shallower ones at lower frequencies. Phase fluctuations tend to result in steeper spectra, while amplitude scintillations lead to shallower spectra. The study suggests a simple model of radio wave propagation through a turbulent ionosphere to explain these observations. Key Points: Dual power‐law spectra observed in phase scintillation in the auroral regionResolving the distinction between refractive and diffractive effects on dual power‐law phase spectraIonospheric irregularities and their connection to amplitude and phase scintillation [ABSTRACT FROM AUTHOR]

The characteristics of a polarized radio wave detected by an antenna onboard a spacecraft depend on the relative positions of the transmitting source and the spacecraft, the orientation of the satellite antenna with respect to the wave propagation direction, the electric field of the incident wave, and the properties of the medium traversed by the wave. Precise knowledge of the radio wave propagation direction and the receiver antenna orientation is needed for resolving the received signal properties. In this work, the focus is on the coordinated experiments between the Radio Receiver Instrument (RRI) on Swarm-E and the Natural Resources Canada Ottawa transmitter (45.4°N, 75.6°W). Three experiments, in which the RRI boresight was along the ram (13 December 2017), nadir (20 December 2017) and slew-to-target (21 December 2017) directions were selected for detailed investigations and comparisons. The deviation of the RRI boresight direction from the propagation direction of the wave vector was up to 10° in the slewed pass and varied between 0° and 180° in the two other passes. The effects of the antenna pointing direction were pronounced in the observed powers on each dipole and affected the observed (apparent) polarization characteristics. The observations were not sufficient for describing the polarization state of the original signal during one third of the RRI-ram experiment when only one dipole was receiving the signal with optimal geometry. The methods developed lay the foundation for mitigating the attitude effects to determine the true polarization characteristics of the radio wave. [ABSTRACT FROM AUTHOR]

This paper focuses on the decomposition of different modes of Loran-C resultant waves, including ground waves and onehop/two-hop sky waves, propagating in the Earth-ionosphere waveguide obtained from direct finite-difference time-domain (FDTD) modeling in the presence of the natural magnetic field. After providing the FDTD iterative formulas for the ionosphere affected by the natural magnetic field, the Loran-C resultant waves propagating in the anisotropic Earth-ionosphere waveguide are estimated using the FDTD algorithm. In both the daytime and nighttime ionosphere models, different orientations of the natural magnetic field are taken into account. The arrival times of the different propagation modes for the resultant waves were then determined using a multipath time-delay estimation method. With the above delays, the amplitudes of the different modes are acquired by solving overdetermined equations. Finally, the decomposition results are compared with those obtained in the absence of the natural magnetic field. The numerical experimental results indicate that, with a radiation power of 1 kW and a natural magnetic field of 0.5 Gs, the influence of the direction of the natural magnetic field on the field strength of one-hop sky waves is significant when the propagation distance of LF radio waves is less than 1000 km. Radio waves have multipath effects such as convergence, divergence, and diffraction due to the curvature of the Earth and the ionosphere. This results in significant interference phenomena when the propagation distance of two-hop sky waves is greater than 500 km. [ABSTRACT FROM AUTHOR]

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The Very Low Frequency (VLF) radio wave propagation characteristics play a very important role in understanding the behaviour of the D-region. The earth-ionosphere wave guide theory has been used to evaluate the reflection height of VLF radio waves using the electron density profiles obtained from the International Reference Ionosphere (IRI) 2012 and 2016 models. For calculating the conductivity parameter, two different collision frequency models have been used. The diurnal shift in reflection height of 16-kHz VLF waves is evaluated for the midpoint of Visakhapatnam-Rugby path using the two IRI models and the results are compared with those values derived from VLF phase measurements made at Visakhapatnam. The theoretically evaluated values using the FT-2001 option for the D-region electron density profile in the IRI-2012 and IRI–2016 models are in good agreement with those obtained from phase measurements, especially in summer. The day to night shift in reflection height obtained using exponential collision critical frequency model are in good agreement with those derived from VLF phase measurements. The diurnal shift in reflection height of VLF radio waves during winter months derived from IRI models are much lower than those obtained from measurements. [ABSTRACT FROM AUTHOR]

It has long been known that field-aligned irregularities within equatorial plasma bubbles (EPBs) can cause long-range propagation of radio waves in the VHF frequencies such as those used for TV broadcasting through the so-called forward scattering process. However, no attempt has been made to use such anomalous propagations of VHF radio waves for wide-area monitoring of EPBs. In this study, we investigated the feasibility of monitoring of EPBs using VHF radio waves used for aeronautical navigation systems such as VHF Omnidirectional radio Range (VOR). There are 370 VOR stations in the Eastern and Southeastern Asian region that can be potentially used as Tx stations for the observations of anomalous propagation. We have examined the forward scattering conditions of VHF waves using the magnetic field model and confirmed that it is possible to observe the EPB-related anomalous propagation if we set up Rx stations in Okinawa (Japan), Taiwan, and Thailand. During test observations conducted in Okinawa since 2021, no signal has been received that was clearly caused by anomalous propagation due to EPBs. This is simply because EPBs have not developed to high latitudes during the observation period due to the low solar activity. In March 2023, however, possible indications of EPB-related scattering were detected in Okinawa which implies the feasibility of observing EPBs with the current observation system. We plan to conduct pilot observations in Taiwan and Thailand in future to further evaluate the feasibility of this monitoring technique. [ABSTRACT FROM AUTHOR]

Currently in Ukraine, taking into account the development of the latest mobile Internet standards (3G/4G), it is possible to access the Internet even in remote places. There are no wired Internet due to the high cost of installation and maintenance. At the same time, a huge amount of equipment appeared on the market, which allows you to assemble systems for obtaining high-quality Internet over a wireless communication line. This refers to various types of antennas in the 900–2700MHz range, modems and routers with 3G/4G support. The locations of 3G/4G Internet base stations are in district centers predominantly. So, there is a situation that remote villages, settlements do not have the opportunity to get access to high-speed Internet. This especially harms the work of biological stations and rural medical clinics, which are spread over the territory of Ukraine and are often connected in a network. The purpose of the work is to describe briefly some practical results of our own development of providing high-quality mobile communication in some remote places of the territory of the state. To provide this service in remote areas of Ukraine, signal amplification is necessary. In addition, there is a problem with the propagation of radio waves over the rough terrains for the ultra short wave and microwave ranges. To solve this problem, it is proposed to use an external antenna with a high amplification factor, which will be installed at a height of at least 6 meters above the ground to reduce the impact of interference on the path of radio waves. [ABSTRACT FROM AUTHOR]

The frequency dependence of transmitted information qualitative indicators is analyzed on the example of two meridional radio links: single-hop (~2600 km) and dominant two-hop (~5100 km) for basic modes of radio wave propagation in the ionosphere. It is shown that the presence of highly efficient receiving-transmitting antennas in a radio communication system leads to the need to take the existence of a priori energetically extremely weak modes into account in the problem of radio path specification statement. In this case, we consider those formed exclusively by the mechanism of radiation transfer along the upper-angles ray trajectories in the ionospheric propagation of radio waves. If the angles of departure and arrival for such modes and the directions of the main lobes of the antenna patterns at the end points of the radio path coincide, the signal-to-noise ratio for the wave field can reach the required threshold value and ensure the successful operation of the radio communication system. This may expand the upper frequency limit for the passage of radio waves in the transition regions of jump propagation of radio waves in the ionosphere; it should be taken into account in forecasting the operation of ionospheric radio links. [ABSTRACT FROM AUTHOR]

Radio propagation in the millimeter wave and subterahertz domain is heavily affected by shadowing conditions. The communication link is blocked without any additional technical means being used. Coverage improvements can be provided by using reflectors, RIS arrays, and repeaters to direct radio waves around corners or obstacles. These concepts show different performance and complexity levels affecting their network deployment. This paper investigates the achievable radio range or the received power to compare specific deployment concepts under realistic propagation conditions. Overall, the repeater solution provides either the largest radio range or the lowest necessary total transmit power compared to reflectors or RIS arrays and, thereby, is the most sustainable approach. A RIS array requires an additional centralized signal processing capacity for calculating optimized RIS settings and results in the highest level of network deployment complexity. [ABSTRACT FROM AUTHOR]

Dramatic irregularities in the plasma density of the ionosphere, first discovered by their effects on radio wave propagation in 1938, despite decades of investigation, still remain puzzling. Their deleterious effects on radio wave communication, satellite command and control, and GPS navigation strongly motivate better understanding of their nature. Many aspects of such irregularities are now understood, but the mechanism(s) of their formation and their detailed nature remain a topic of great interest. In this work, detailed time resolved measurements of lightning generated waves sometimes show dispersionless, strongly attenuated propagation with substantial propagation delays. These characteristics of the electromagnetic wave propagation in the hypothetical two‐phase bubble/non‐bubble lower ionosphere parallel the characteristics of acoustic wave propagation through two‐phase liquid/vapor foams. This motivates the suggestion that the bottomside layer of the ionosphere may sometimes be foamy. Plain Language Summary: Just as ocean waves breaking at the interface between sea and land produce copious bubbles and foam, recent satellite data suggests a similar phenomenon at the interface between neutral atmosphere and the charged plasma of the ionosphere. Lightning generated electromagnetic waves passing through the lower ionosphere observed by low altitude satellites are found to have the same characteristics as acoustic waves passing through foamy water. This hypothetical foam in the lower ionosphere apparently strongly absorbs some radio wave frequencies and seems to prevent most such waves from escaping the foam to pass through to the upper ionosphere. Key Points: Dispersionless, highly attenuated, lightning generated electromagnetic waves are observed in the lower ionosphereThe propagation of these electromagnetic waves has characteristics of acoustic wave propagation through two‐phase foamsSuch foamy plasma bubbles may cover approximately 85% of the bottomside of the equatorial nightside ionosphere [ABSTRACT FROM AUTHOR]

A special analytical method is developed to describe the propagation of high-frequency electromagnetic waves emitted by a vertical point dipole from the surface of perfectly conducting Earth in a regular spherically layered background ionosphere. The basic representation of the wave field employs an integral over the set of wave components, each of which is related to a specific ray trajectory. Such an approach makes it possible to analytically take into account the effect of medium-scale 3D inclusions in the background ionosphere as an additional phase shift of the wave component with allowance for the distortion of its ray trajectory and to numerically calculate the effect of wave-field focusing. [ABSTRACT FROM AUTHOR]

The method of bicharacteristics is used to study the propagation of decameter radio waves in the ionosphere containing the E, F1, and F2 layers and a traveling ionospheric disturbance (TID) upon slightly oblique sounding with frequency-modulated signals. The propagation of both ordinary and extraordinary waves is considered, the ionograms are compared, and their relative shift is studied. The structure of ionograms in the vicinity of caustics, which appear at the reception point at frequencies reflected in the vicinity of the E layer and TID, is studied. The divergence of the ray flux at the point of radiation reception, which determines a decrease in the amplitude, is calculated. [ABSTRACT FROM AUTHOR]

Conventional forecasting of high‐frequency (HF, 3–30 MHz) radio wave propagation is based on a combination of ionospheric and propagation models. However, at very high latitudes this approach is seriously undermined by the intrinsically dynamic ionospheric conditions regularly perturbed by energetic particle precipitations and strong electric fields. From this perspective, the multi‐year observations of HF propagation characteristics by Super Dual Auroral Radar Network (SuperDARN) radars across auroral and polar cap regions represent a unique opportunity for systematic validation of the conventional approach, as well as for creating an empirical propagation model directly from the radar observations. Qualitative identification and quantitative characterization of the propagation modes requires an accurate knowledge of the vertical angle of arrival (elevation angle) across the high‐latitude part of the radar network. This information has become available only in recent years, facilitated by the development of reliable data‐based calibration techniques for SuperDARN interferometry. We present the solar‐cycle/seasonal/diurnal climatology of HF propagation characteristics at very high latitudes derived from two‐frequency observations by the Rankin Inlet SuperDARN radar. Plain Language Summary: High‐frequency (HF, 3–30 MHz) radio waves are used for long‐distance communication, navigation and surveillance purposes, as they can propagate over the horizon due to consecutive reflections from the ionosphere and the ground surface. The conventional forecast of HF propagation at mid and low latitudes relies on ionospheric models that are used to derive HF propagation characteristics. However, this approach becomes less reliable at auroral and polar cap latitudes due to the intrinsically high variability of the high‐latitude ionosphere. In this work we lay an experimental foundation for an alternative propagation model based on direct observations of the HF propagation characteristics by Super Dual Auroral Radar Network (SuperDARN). This approach eliminates the necessity of using an ionospheric model by utilizing accurate SuperDARN angle‐of‐arrival information obtained for a full solar cycle. Key Points: Modeling high‐frequency (HF) propagation at very high latitudes is complicated by highly dynamic processes in the ionospheric plasmaSuperDARN represents a convenient tool for direct observations of HF propagation characteristicsSuperDARN interferometry data are utilized to build a climatological model of HF propagation [ABSTRACT FROM AUTHOR]

Using data from the Van Allen Probe and Swarm‐Bravo satellites, evidence for a persistent population of slow magnetosonic waves in the ionosphere is presented. Dispersion relations from two‐fluid analyses of waves in warm plasma are used to interpret and explicate these observations. These waves appear to be continuously present and globally distributed. Their amplitudes systematically decrease with increasing altitude. The amplitudes are also correlated with longitude in a manner consistent with the global distribution of lightning strikes. Evidence for narrow resonances in the Swarm data consistent with doppler shifted Schumann resonance frequencies is presented. In addition, nearly dispersionless fast magnetosonic waves are sometimes also seen. A new method for the analysis of these waves suggests they show the existence of "foamy" plasma bubble "roots" at the base of the ionosphere. Plain Language Summary: Using satellite data, just as the acoustic noise from distant lightning is heard to rumble, sometimes a considerable time later, for a much longer duration than the visible flashes, an even more greatly delayed and spread‐out series of plasma‐sound waves are found in the earth's ionosphere after every lightning bolt. The noise of these plasma‐sound waves comes in two forms. One set of plasma‐sound waves is slow and is found to be always present over the entire globe. Properly accounting for this noise in satellite electromagnetic field measurements could improve the quality of measurements of the earth's magnetic field from space, and lead to a better understanding of our earth's magnetic field and its ionosphere. A second set of plasma‐sound waves is fast, and more sporadic in appearance. These fast plasma‐sound waves are associated with plasma bubbles that can interfere with radio wave communications around the globe. Better understanding these fast waves and bubbles could possibly allow for better radio communication processes. Key Points: Globally distributed slow magnetosonic waves in the ionosphere have been found with amplitudes decreasing versus altitudeIt is suggested that these are produced by lightning generated waves impacting the Earth Ionosphere waveguide upper boundaryUnusual low dispersion whistlers suggest the existence of plasma depletion "roots" extending to the base of the ionosphere [ABSTRACT FROM AUTHOR]

In order to improve the identification effect of vehicle key performance parameters, this paper applies the PSO algorithm to the identification of vehicle key performance parameters and focuses on analyzing the parameters of the vehicle key performance parameter monitoring equipment and the propagation environment. The improvement of sensitivity of the monitoring receiver can effectively extend the coverage distance. NLOS is a ubiquitous transmission environment and changing NLOS to LOS propagation further extends the coverage distance. In order to ensure the communication quality of radio communication users, ensure that the service area covered by radio waves and the reliability of radio wave propagation, this paper calculates the propagation loss from the receiving antenna to the transmitting antenna in detail. The experimental results show that the identification method of vehicle key performance parameters based on PSO algorithm proposed in this paper can play an important role in the identification of vehicle key performance parameters. [ABSTRACT FROM AUTHOR]

Gravity waves, which are considered omnipresent in the Earth's upper atmosphere, are generally investigated by monitoring the fluctuations in different atmospheric parameters. Here, we report the propagation characteristics of thermospheric gravity waves both in horizontal and vertical directions obtained using collocated optical and radio measurements from Ahmedabad, India for February 2021. The measurements of OI 630.0 nm dayglow emission rates over zenith are used to derive time periods of gravity waves. Wave number analyses of variations in the emission over a large field‐of‐view have been performed to derive gravity wave scale sizes and propagation characteristics in the horizontal direction. Time periods, horizontal scale sizes, and propagation directions are found to be in the range of 31–125 min, 78–243 km, and 203°–248° from east, respectively. Vertical wavelengths of the gravity waves are obtained from radio measurements and are in the range of 26–247 km. As the gravity wave characteristics are influenced by the ambient neutral winds, the measured gravity wave propagation characteristics in three dimensions have been used as inputs into the gravity wave dispersion relation to estimate the magnitudes of thermospheric horizontal neutral winds. These estimated daytime winds in the direction of wave propagation are found to be in the range of 1–105 ms−1, and they compare well with those measured independently from MIGHTI added HWM14 model‐derived winds. The daytime winds estimated by this approach are possibly the first of their kind as obtained from ground‐based measurements. Plain Language Summary: Atmospheric gravity waves are mostly generated in the lower atmosphere due to different processes, and they carry energy away from their source regions. Therefore, these waves play a crucial role in the coupling and energetics of the atmosphere. As the neutral density decreases exponentially with height, amplitudes of these waves grow in order to conserve energy. At high altitudes, when the amplitudes become very large, these waves break due to non‐linear wave‐wave interactions and deposit their energy. Such energy deposition can further give rise to secondary and tertiary gravity waves. In favorable background conditions, these waves can propagate deep into the upper atmosphere and alter the prevailing dynamics. Therefore, the characterization of their spatial and temporal scales in the upper atmosphere is extremely important for a comprehensive understanding of atmospheric dynamics. As neutrals and plasma share the same space in the upper atmosphere, we have used simultaneous observations of both the neutrals and plasma, using ground‐based optical and radio measurements, to derive the propagation characteristics of the atmospheric gravity waves in all three dimensions. Further, we have used these parameters to estimate the magnitudes of daytime thermospheric horizontal winds, which are otherwise difficult to obtain from ground‐based platforms in daytime. Key Points: Three‐dimensional characterization of daytime thermospheric gravity waves has been made using collocated optical and radio measurementsEstimated vertical wavelengths of gravity waves from their horizontal characteristics reasonably match with those measured from digisondeThermospheric neutral winds estimated using measured 3‐D gravity wave information show a good match with those measured by MIGHTI [ABSTRACT FROM AUTHOR]

Plasma bubbles are large‐scale irregular structures that often occur at equatorial latitudes, equatorial plasma bubbles (EPBs) affect the propagation of high‐frequency (HF) radio waves. Based on their main observational characteristics, a three‐dimensional (3D) model of EPBs was established, and a preliminary simulation of EPBs was performed. Three‐dimensional ray tracing can be used to simulate HF radio wave propagation. In this study, we consider EPBs at different scales, appearing at different times and different heights, and investigate the influence of EPBs on the propagation path of radio waves at low latitudes. The simulation results show that when they propagate through EPBs of different scales, the propagation paths of radio waves are completely different. Radio waves at 6, 8, and 10 MHz show obvious refraction; With an increase in EPB scale, the focusing effect of radio waves will diminish, and the focusing height will increase. The propagation of HF radio waves through EPB change with time as follows: partial penetration, partial reflection, and total penetration, the refraction effect of EPB on radio waves gradually decreases over time. When radio waves propagate through EPB at different heights, the simulation results show that EPB at an altitude of 200 km makes little impact on the radio waves. As the height of EPB increases, the radio waves will exhibit significant refraction, showing an obvious focusing effect. Key Points: The influence of plasma bubbles on radio wave propagation can be simulated by three‐dimensional ray tracingRadio waves propagating through plasma bubbles exhibit significant refraction, showing an obvious focusing effectWith the increase in radio frequency, the focusing effect of radio waves will diminish, and the focusing height will increase [ABSTRACT FROM AUTHOR]

One of the technologies used for localization is GNSS (Global Navigation Satellite Systems), which is exposed to many phenomena, i.e., the occurrence of terrain covers, reflections of the radio waves, and the multipath nature of the radio waves in the propagation environment. To increase the resistance to environmental phenomena, special types of antennas are used, which include, among others, choke ring antennas. The article describes the design and construction of the choke ring antenna and the impact of the mentioned device on the quality of GNSS positioning. The accuracy of the constructed antenna (based on selected accuracy measures: DRMS, 2DRMS, SEP, MRSE, SAE) is calculated together with positioning errors determined for two types of antennas: choke ring antenna and the dedicated antenna supplied by the manufacturer in RTK mode. The results confirm that the designed choke ring antenna can be used for positioning without significantly losing accuracy in the RTK mode. [ABSTRACT FROM AUTHOR]

The production of crops in greenhouses will ensure the demand for food for the world's population in the coming decades. Precision agriculture is an important tool for this purpose, supported among other things, by the technology of wireless sensor networks (WSN) in the monitoring of agronomic parameters. Therefore, prior planning of the deployment of WSN nodes is relevant because their coverage decreases when the radio waves are attenuated by the foliage of the plantation. In that sense, the method proposed in this study applies Deep Learning to develop an empirical model of radio wave attenuation when it crosses vegetation that includes height and distance between the transceivers of the WSN nodes. The model quality is expressed via the parameters cross-validation, R2 of 0.966, while its generalized error is 0.920 verifying the reliability of the empirical model. [ABSTRACT FROM AUTHOR]

Due to the inhomogeneity of the atmosphere, radio waves are subjected to refraction during the propagation process, which reduces its propagation speed and bends the propagation path. If the influence is not considered, a large error will be caused by using time difference of arrival (TDOA). The influence of atmospheric refraction on the TDOA localization under the known elevation constraint is analyzed, a subsection iterative method is proposed to correct the localization error caused by atmospheric refraction, the Cramer-Rao lower bound (CRLB) for location estimation under atmospheric refraction is deduced. The effectiveness of the proposed method is validated through simulation results and analysis. [ABSTRACT FROM AUTHOR]

The group velocity of lightning electromagnetic signals plays an important role in lightning location systems using the time difference of arrival (TDOA) method. Accurate estimation of group velocity is difficult due to the space- and time-varying properties of the Earth-ionosphere waveguide. Besides, the analytical solution of the group velocity is difficult to obtain from the classic mode theory, especially when higher-order modes, anisotropic geomagnetic background, diffuse ionosphere profile, and propagation path segmentation are all taken into consideration. To overcome these challenges, a novel numerical method is proposed in this paper to estimate the group velocity of the lightning signal during ionospheric quiet periods. The well-known Long Wavelength Propagation Capability (LWPC) code is used to model the propagation of VLF/LF radio waves. Since LWPC uses a simplified ionospheric model which is unable to describe the subtle variations of ionospheric parameters over time and space, the IRI-2016 model is incorporated into the numerical modeling process to provide more accurate ionosphere parameters. Experimental results of a VLF/LF lightning location network are demonstrated and analyzed to show the effectiveness of our method. The proposed method is also applicable when there is a sudden ionospheric disturbance as long as the parameters of the ionosphere are obtained in real time by remote sensing methods. [ABSTRACT FROM AUTHOR]

The dust‐laden and predominantly water ice south polar layered deposits (SPLD) exhibit unique radar behavior at Shallow Radar (SHARAD) frequencies that is not seen in the NPLD. A vertically extensive scattering phenomenon leads to diffuse echoes that obscure radar stratigraphy within the SPLD, referred to as "fog." Here, we use 2‐D and 3‐D SHARAD data to measure the areal extent in which the SPLD basal interface can be identified. We also measure reflected power of SPLD basal reflectors and compare those values to ice thickness, regional geomorphology, and the presence of radar echo scattering, to constrain any influence these factors may have on the propagation of radio waves and detectability of the base. Approximately 33% of the area in which the basal interface is observed in Mars Advanced Radar for Subsurface and Ionosphere Sounding data is also detected in SHARAD data. As expected, basal power shows a negative correlation with ice thickness, but the effects of radar fog are less clear. Areas of "column" radar fog patterns exhibit higher average basal power values than regions without radar fog, and areas with only near‐surface radar fog have the lowest average basal power values. Our study results suggest that these diffuse echoes may not be associated with radio wave attenuation. Average loss tangent for the SPLD (0.0019 ± 0.0012) indicates no distinguishable difference from previously reported NPLD values in terms of bulk loss properties. We speculate that the SPLD's infrequent reflections compared to the NPLD may be due to the former's dust being less densely packed together to facilitate radar detection. Plain Language Summary: The interior structure of Mars' dusty, water ice polar caps can be observed using radar instruments currently in Martian orbit. We use cross section images called radargrams to observe the strength (brightness) of the signal reflected from cap's surface and interior layers. One of these instruments exhibits different behavior in radargrams between the two caps: the southern cap produces a mysterious fog‐like radar signal that is not seen in the north. We use the relative brightness between layers within the caps to determine if the radar fog is associated with a greater amount of signal loss. We do see more loss as ice thickness increases, but we don't find the same association with the presence of radar fog. Additionally, our inability to see the base of the cap in our data also does not appear to be related to radar fog. We find that both polar caps as wholes exhibit similar radar properties, despite looking very different in radargrams. We suggest that the southern cap may have less densely packed dust within its layering. Key Points: The occurrence of a fog‐like phenomenon in radargrams is not associated with diminished reflector detectability or enhanced signal lossBulk loss tangents between the south polar layered deposits (SPLD) and NPLD are similar, indicating similar bulk radar propertiesLess frequent reflections in the SPLD might be due to dust being less densely packed relative to the NPLD [ABSTRACT FROM AUTHOR]

A communication blackout is one of the major problems that occurs during the reentry of a satellite into the Earth's atmosphere, which is caused by the reentry plasma blocking electromagnetic waves near the satellite for telecommunication. Moreover, it prevents tracking and data transmission, resulting in inaccurate prediction of landing sites and data loss. Therefore, there is a necessity to evaluate the propagation of electromagnetic waves in the reentry plasma and to mitigate the communication blackout. An inflatable aeroshell technology with lightweight and large-area features enables aerodynamic drag at high altitudes to reduce aerodynamic heating and to mitigate communication blackouts. Thus, a nanosatellite mission using such an inflatable aeroshell has been proposed. For the purpose of telecommunication possibilities during the reentry in future nanosatellite missions, a detailed investigation of communication blackout mitigation by inflatable aeroshell is required. In the present article, the plasma flow and electromagnetic wave propagation near the nanosatellite during atmospheric reentry were revealed by using a computational science approach. A low-temperature and low-density wake is formed behind the nanosatellite. Moreover, an electromagnetic wave propagation path is formed in the wake, indicating that this path is maintained during the reentry, and no communication blackout occurs when using the deployable nanosatellite. [ABSTRACT FROM AUTHOR]

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs. [ABSTRACT FROM AUTHOR]

The Harbin Engineering University, the People's Republic of China, multifrequency multiple‐path coherent radio system operates continuously and provides data for post analysis. The data collected during the solar eclipse of 21 June 2020 have been chosen for this study with the objectives to interpret the variations in the Doppler spectra, Doppler shift, and in the reflected radio wave amplitudes that are associated with the solar eclipse, establish the magnitude and find physical significance of these variations, determine the reduction in the electron density caused by the solar eclipse, and to estimate an increase in wave activity in the ionosphere. The eclipse was accompanied by Doppler spectrum diffuseness resulting from an increase in the number of rays, the temporal variations in the Doppler shift were observed to be bi‐polar, asymmetrical, and anomalously small, with extreme Doppler shift magnitudes varying from −11 to −40 mHz and from 22 to 56 mHz. The duration of processes with negative Doppler shifts varied from 50 to 80 min, and the duration of processes with positive Doppler shifts changed from 30 to 80 min. The multi‐hop propagation (from two to five hops) took place along all propagation paths, with a 360 to 560‐km one‐hop length, due to the anomalous radio wave propagation via the sporadic‐E layer present about 80% of the time on 21 June 2020. The Doppler shift exhibited 4–18‐min period quasi‐sinusoidal variations with 20–10‐mHz amplitudes. Plain Language Summary: In the past, the study of the influence of eclipses on the ionosphere seemed to be a rather simple subject because a solar eclipse seemed to be just mimicking night, although over a shorter time interval. Subsequently, the movement of the solar terminators has been discovered to generate atmospheric gravity waves, which is also true for eclipses. Recent advances in instrumentation and measurement techniques have facilitated the revelation of unusual and interesting phenomena that do not necessarily belong to nighttime conditions. For example, in this study, we have discovered, along with the determination of specific changes in the atmospheric and radio wave parameters, that temporal variations in the Doppler shift were bi‐polar, asymmetrical, and anomalously small. Key Points: Doppler shift variations were bi‐polar, asymmetrical, and anomalously small, with extremes varying from −11 to −40 MHz and from 22 to 56 MHzMulti‐hop propagation (from two to five hops) took place along all propagation paths, with a length of one hop varying from 360 to 560 kmAn electron density decrease was determined to vary from –(12–16)% to –(20–26)% along different propagation paths [ABSTRACT FROM AUTHOR]

The demand for more radio spectrum bandwidths has risen as a result of recent developments in wireless technology from every field of the wireless industry. It's getting faster by the day, and we're on our way to greater mobility as the market for higher data rates grows. The growth of the internet has increase demand for wireless networks, causing the available radio spectrum to become increasingly congested. Various studies have found that the rising demand for spectrum is due to regulatory schemes put in place by authorities to protect the rapidly growing number of spectrum users. Researchers are putting in a lot of effort to establish a methodology for coping with the looming spectrum crisis. Several regulators have recently expressed interest in funding free radio channels to give unlicensed devices entry. Clouds, hail, dust, gases, and other troposphere phenomena are more vulnerable to frequencies above 10 GHz. The effect of these phenomena on radio wave propagation in the troposphere is discussed in this paper. The results of various studies in this area are examined in this review.We have indicated "Vivek Kumar" as corresponding author. Please check and confirm.ok confirmed [ABSTRACT FROM AUTHOR]

Given the massive rapid growth for capacity in wireless data telecommunications every year, wireless carriers must be planned for a thousand-fold increase in mobile traffic in 2020. It compels scientists to explore for new wireless airwaves that can accommodate large data rates. Next-generation technologies must address issues such as increased spectrum allocation in millimetre wave frequency bands, the installation of directional antennas beam forming antennas, better battery life, high data transmission rates with reduced outage probability, lower capital costs, and increased capacity for multiple simultaneous users. There are two types of telecommunication links: terrestrial and satellite. Terrestrial links are also known as radio relay links. This connects the troposphere, which is located between the earth's surface and the high atmosphere, to the propagation of radio waves. Gases, water vapour, and other weather phenomena such as rain, storms, snow, and hail all interfere with higher frequency radio signals in this region. Due to these difficulties, energy is absorbed and diffused, resulting in signal attenuation. Another form of obstruction generated by radio waves on terrestrial paths is buildings, trees, lampposts, grill, and other urban features. Under these conditions, reflection, diffraction, refraction, scattering, depolarization, and other phenomena are studied. This study discusses the effects of rain on satellite and terrestrial communications. [ABSTRACT FROM AUTHOR]

Using atmospheric data, which include pressure, temperature, relative humidity and water vapor pressure, the actual refractive index of a specific segment of the atmosphere has been modeled. Based on the refractive index, a numerical method is presented to quickly estimate the propagation path of the radio wave in the troposphere. Utilizing the terrain and the surface medium model of the propagation area and the parabolic equation (PE) method, an image of the electric field distribution of radio waves in the troposphere is obtained. A comparison of propagation paths between the numerical method and the PE model is presented. Additionally, the effects of the antenna's elevation angle have been studied. Physical measurements provide a reference for the accuracy of the simulation results obtained using the method presented in this work. [ABSTRACT FROM AUTHOR]

We acquired measurements of four observable parameters of refracted signals received from the ionosphere (Doppler shift, Doppler spectrum, number of rays, and signal amplitude) with the oblique HF Doppler technique in the city of Harbin during the super typhoon Lekima event of 4–12 August 2019. The ionospheric response was observed by the Harbin Engineering University multifrequency multiple path coherent radio system in the People's Republic of China. The maximum distortion of radio‐wave characteristics and ionospheric disturbances were observed to occur during the day when the super typhoon Lekima energy gained a maximum value and when the super typhoon approached close to the ionospheric part of the radio‐wave propagation paths. The magnitude of the ionospheric disturbances decreased with the distance between the super typhoon and propagation path midpoints. Both aperiodic (chaotic) and quasi‐sinusoidal disturbances were observed to accompany the action of the super typhoon in the ionosphere. The action of the typhoon was often accompanied by up to ±1.5 Hz broadening of the Doppler spectra, 10–30 dBV variations in the signal amplitude, and quasi‐sinusoidal variations in the Doppler shift with 0.10‐ to 0.40‐Hz amplitudes and periods of 20–30 to 70–80 min. The quasi‐sinusoidal variations in the signal amplitude with a ∼24‐min period, T, are due to focusing and defocusing of rays by wavelike disturbances in the electron density. The periods of the quasi‐sinusoidal disturbances were observed to be ∼12–24 min. Such periods pertain to atmospheric gravity waves. The atmospheric gravity waves generated by the super typhoon gave rise to quasi‐sinusoidal variations in the electron density with relative amplitudes of ∼3%–∼19%. Plain Language Summary: Typhoons pertain to high‐energy sources that are capable of giving rise to perturbations in all geospheres. The disturbances produced in the atmosphere and geospace make a significant contribution to the state of space weather, whereas the ionospheric perturbations have a drastic effect on the propagation of HF radio waves. We have used super typhoon Lekima, which took place during the 4–12 August 2019 period, to demonstrate some of the many disturbing influences that typhoons have on the state of space weather and the propagation of HF radio waves. The multifrequency multi path observations have been taken by the coherent radio system located at the city of Harbin (People's Republic of China). Key Points: Atmospheric gravity waves launched by the typhoon Lekima produced ∼3%–∼19% quasi‐sinusoidal electron density variationsSpectrum broadening attained ±1.5 Hz, and Doppler shift varied with 0.10–0.40‐Hz amplitudes and 20–30‐ to 70–80‐min periodsThe action of the super typhoon Lekima was accompanied by 10–30 dBV variations in the signal amplitude [ABSTRACT FROM AUTHOR]

In this paper, the ionospheric disturbances of CO2, which is released by rocket exhaust plumes, was simulated. The effect of this disturbance on the propagation of high-frequency (HF) radio waves at different incident frequencies was also simulated by using three-dimensional digital ray tracing technique. The results show that CO2 can effectively dissipate the background electrons and form ionospheric holes after being released in the ionosphere. At the peak height of ionospheric electron density (about 300 km), the electrons are dissipated fastest and the radius of ionospheric hole is also largest. This is due to the fact that the diffusion coefficient of CO2 usually increases with height while the electron density just increases before reaching its peak height and then decreases with height, and the chemical reaction rate between ions and CO2 also becomes largest at the peak height of electron density (about 300 km). Around 100 s after the release of CO2, when the radio waves at a frequency of 8 MHz pass through the ionosphere with an elevation range of 85~95°, the "secondary focusing effect" can occur, and we believe that this is due to the reflection of HF shortwaves on the walls of the ionospheric holes. With time going on, this phenomenon disappears at 300 s and only one focus is left at this time. For the HF shortwaves at same incident frequency, the focusing effect of waves displays a weakening trend with time increasing, and the height of focus center also ascends gradually. At the same time after CO2 releasing, with the increasing of radio waves frequency, the focusing effect also becomes weaker and the focus center displays an ascending trend. [ABSTRACT FROM AUTHOR]

This paper explained an adaptive ray tracing technique in modelling indoor radio wave propagation. As compared with conventional ray tracing approach, the presented ray tracing approach offers an optimized method to trace the travelling radio signal by introducing flexibility and adaptive features in ray launching algorithm in modelling the radio wave for indoor scenarios. The simulation result was compared with measurements data for verification. By analyzing the results, the proposed adaptive technique showed a better improvement in simulation time, power level and coverage in modelling the radio wave propagation for indoor scenario and may benefit in the development of signal propagation simulators for future technologies. [ABSTRACT FROM AUTHOR]

We have developed a model that simulates the Poynting flux profile of the Saskatoon Super Dual Auroral Radar Network (SuperDARN) radar at ionospheric altitudes. The model uses ray tracing software to project the radar system's vacuum Poynting flux profile through the ionosphere, taking into account the influence of the ionospheric medium on the propagation characteristics of the high frequency radio waves. Measurements of the radar's transmissions by the Radio Receiver Instrument (RRI) in low‐Earth orbit are used to validate the model during five experiments which occurred between 4 and 8 August 2017. Comparisons between simulated and measured RRI antenna voltages show good agreement, although there are clear instances in which the model underperforms. Nevertheless, the model demonstrates its utility as a tool for interpreting RRI measurements of SuperDARN radars. The model also helps address a lack of knowledge of a SuperDARN radar's Poynting flux profile at ionospheric altitudes. In particular, we assess the assumption that SuperDARN's scattering volume lies along the great‐circle path of the transmitting beam's bearing. Comparisons between the model and RRI's measurements show that this assumption is reasonable for the five experiments investigated in this work. The model presents a new way of carrying out SuperDARN and high frequency radio science investigations. Plain Language Summary: The Super Dual Auroral Radar Network (SuperDARN) radar system located in Saskatoon, Canada is a powerful tool for studying the high‐latitude ionosphere. Even though the system has been operating nearly continuously since 1993, there is very little understanding of what the radar's Poynting flux profile looks like at ionospheric altitudes where its radar echoes originate. This is simply due to a lack of available measurements. As a result, it is customary to simply assume that the radar's Poynting flux profile at ionospheric altitudes resembles that of its Poynting flux profile in a vacuum projected along great‐circle trajectories up to ionospheric altitudes. This assumption is limited because it does not adequately account for the fact that the radar's Poynting flux profile can be influenced by the ionospheric medium in which it is immersed. In this work, we have developed a model of Saskatoon SuperDARN's Poynting flux profile at ionospheric altitudes which properly accounts for the influence of the ionosphere. Furthermore, we have compared the model's output to several measurements of the Saskatoon radar made by a radio receiver in low‐Earth orbit to validate the model. Our results show that the model is accurate and can be used as a useful tool for studying SuperDARN's Poynting flux profile at ionospheric altitudes. Key Points: The Saskatoon Super Dual Auroral Radar Network radar's Poynting flux profile is modeled in an empirical ionosphereA simulated Poynting flux profile is validated with the Enhanced Polar Outflow Probe Radio Receiver InstrumentThe Poynting flux model is a useful tool for studying high frequency radio wave propagation [ABSTRACT FROM AUTHOR]

The interaction of radio frequency waves as it propagates through a plasma medium – has fascinated the plasma physicists for decades. The ionosphere is crucial for radio wave propagation. Short radio waves reflect from the F-layer and spread over long distances (up to two-three thousand kilometers) due to a high altitude of the layer. Long and medium radio waves propagate in the E- and D-layers. The anisotropy of ionospheric plasma due to the Earth's magnetic field accounts for the presence of two radio wave components, ordinary (O-mode) and extraordinary (X-mode). Powerful, high-frequency (HF) radio waves can be used to temporarily modify the ionosphere. These controlled, active experiments have proven useful both for studies of the natural upper atmosphere through observations of the ionospheric response to HF-induced perturbations, and for basic physics investigations exploiting the ionosphere as a large, natural plasma laboratory-without-walls. Here, we study these wonderful aspects through a student project. [ABSTRACT FROM AUTHOR]

With the given scope for new use cases and the demanding needs of future 6th generation (6G) wireless networks, the development of wireless communications looks exciting. The propagation medium has been viewed as a randomly behaving entity between the transmitter and the receiver since traditional wireless technology, degrading the quality of the received signal due to the unpredictable interactions of the broadcast radio waves with the surrounding objects. On the other hand, network operators could now manipulate electromagnetic radiation to remove the negative impacts of natural wireless propagation due to the recent arrival of reconfigurable intelligent surfaces (RIS) in wireless communications. According to recent findings, the RIS mechanism benefits nonorthogonal multiple access (NOMA), which can effectively deliver effective transmissions. For simple design, of RIS-NOMA system, fixed power allocation scheme for NOMA is required. The main system performance metric, i.e., outage probability, needs to be considered to look at the efficiency and capability of transmission mode relying on RIS and NOMA schemes, motivated by the potential of these developing technologies. As major performance metrics, we derive analytical representations of outage probability, and throughput and an accurate approximation is obtained for the outage probability. Numerical results are conducted to validate the exactness of the theoretical analysis. It is found that increasing the higher number of reflecting elements in the RIS can significantly boost the outage probability performance, and the scenario with only the RIS link is also beneficial. In addition, it is desirable to deploy the RIS-NOMA since it is indicated that better performance compared with the traditional multiple access technique. [ABSTRACT FROM AUTHOR]

The plasma sheath formed around a hypersonic vehicle traveling through the atmosphere will affect the quality of wireless signals. To fully grasp this effect, it is necessary to comprise the vehicle antennas in the investigations, which is considered in our work. Firstly, the discrete plasma sheath data is generated by using COMSOL. Then, combining the shift-operator Finite-Difference Time-Domain method and numerical methods such as the high-dimensional Lagrange interpolation, an electromagnetic algorithm designed for the discrete plasma sheath data is developed. Based on this, the influence of the plasma sheath on the radio wave propagation is studied under different flight condition. Results show that, due to the influence both of the plasma sheath and of the vehicle antenna, the radio waves exhibit rich propagation behaviors, such as the frequency-band shift and the tail diffraction, etc. Compared with other studies, the results in this paper more approximately reflect the propagation characteristics of radio waves in the hypersonic environment, and can provide a reference for the related applications. [ABSTRACT FROM AUTHOR]

Extremely low-frequency (ELF: below 30 Hz) wave penetration theory in the layered oceanic lithosphere is essential for studying submarine communications. In this article, we investigate the mode theory of ELF wave propagation in a layered oceanic lithosphere waveguide. Based on the real situation of the oceanic lithosphere approximated by the stratified prototype, in which a low-conductivity layer lies between two overlying and underlying high-conductivity regions, a theoretically sound physical model of oceanic lithosphere waveguide is built. The modal equations for transverse magnetic (TM) and transverse electric (TE) polarized guided modes are delivered using surface impedance boundary conditions. By evaluating the reflection coefficients of the upper and lower waveguide boundaries, formulas for the modal equation’s roots are derived. Analytical expressions for propagable mode parameters, such as the phase velocity, attenuation rate, excitation factor, and the field strength for different components, are obtained, and the cutoff frequency for high-order modes is given. Computations show that the field component curves exhibit typical peaks and nulls associated with multiple-mode propagation in the waveguide region, with each mode traveling at different phase velocities and attenuation rates. Moreover, it is found that all the high-order modes are evanescent below the cutoff frequency. [ABSTRACT FROM AUTHOR]

High frequency (HF; 3–30 MHz) radio wave propagation can be impacted by absorption that results from enhanced photoionization in the dayside D-region following a solar X-ray flare. A database of >25,000 solar X-ray flares was evaluated to characterize the relationship between flare duration and the peak of the 0.1–0.8 nm solar X-ray flux. Expressions describing the mean and 90th percentile duration were developed. Based on these models, mean durations of 13, 18, 27, and 39 min and 90th percentile durations of 30, 48, 77, and 123 min are expected for C1, M1, X 1 and X 10 solar X-ray flares, respectively. A probability distribution of flare durations was developed to describe the probability of flare duration lasting 0–15, 15–30, 30–45, 45–60, 60–90, >90 min. In addition to flare duration, the duration of the expected impact to HF radio waves was evaluated. By considering examples where HF radio wave propagation in the 5–15 MHz range was impacted by space weather, a 0.5 dB threshold at 30 MHz was observed in samples of riometer data. Absorption modelled at 1-min increments from 1986 to 2017 was evaluated to create a probability distribution of impact duration, defined as the length of time the modelled 30 MHz absorption exceeded 0.5 dB during a single event. Modelled absorption was further evaluated to demonstrate the geographic extent of enhanced absorption, and to determine the minimum solar X-ray flux required to exceed the 0.5 dB impact threshold at a given latitude as a function of solar zenith angle and time of year. The results of this paper provide a better understanding of the impact of solar X-ray flares on high frequency radio wave propagation and aid in the development of tools and services for mitigating space weather impacts to systems that rely on HF radio wave propagation. • HF radio wave propagation at 5–15 MHz is impacted when absorption at 30 MHz for a one-way vertical path is ≥ 0.5 dB. • Mean and 90th percentile solar X-ray flare duration were derived as a function of peak 0.1–0.8 nm solar X-ray flux. • The minimum solar X-ray flux expected to impact HF radio waves is evaluated throughout the year for various latitudes. [ABSTRACT FROM AUTHOR]

These studies will also reveal whether there is only a single FRB population, or if there are different FRB progenitors with various formation channels. INSIGHTS ASTRONOMY In just a tiny fraction of a second, a fast radio burst (FRB) in the distant cosmos can emit as much energy as the Sun does in several days. The 16.3-day periodicity observed in FRB 20180916B may also support a binary interaction model for repeating FRBs (11). [Extracted from the article]