Oblique Sounding Research Articles

Trapping of sensing radio waves in an artificial large-scale ionospheric cavity

The results of phenomenological analysis of data from oblique chirp sounding of the ionosphere in a 2007 heating experiment with possible recording of the effect of trapping sounding-radiation in an artificial ionospheric cavity and spotlighting it in the near (over the Earth’s surface) zone of the Sura facility are presented. The physical aspects of forming an additional trace on ionograms of oblique radio-sounding of the perturbed region of the ionosphere are discussed.

THE ELECTRON DENSITY PROFILE INVERSION FOR INCOMPLETELY DEVELOPED CASE OF F1 LAYER

AbstractThe electron density profile inversion from vertical incidence ionograms is essential for research in ionospheric structures and movements, wave propagation and space weather applications, hence has gathered very wide attention. The echo trace of incompletely developed F1 layer is common in vertical incidence ionograms, and it is usually expressed as smooth transition from F1 layer to F2 layer, not a cusp appeared at the critical frequency of F1 layer. However, the existing ionospheric models and inversion algorithms are generally intended for the completely developed F1 layer with the assumptions of a parabolic profile and an infinite slope at the peak of F1 layer, which are not suitable for the profile of incompletely developed F1 layer which achieves the maximum electron density of F1 layer and enters F2 layer at the peak of F1 layer and has a finite slope. Consequently, an F1 layer electron density profile model based on the shifted Chebyshev polynomial for incompletely developed case of F1 layer is introduced with a parameter named as the model setting critical frequency. Taking into account the profile smoothness, an electron density profile inversion algorithm with constrained optimization F1 and F2 layer parameters based on the model mentioned above is proposed. The validity of the model and the inversion algorithm is analyzed through the simulation, and the effectivity of the proposed algorithm is further verified by the comparison between the synthesized vertical sounding & oblique sounding traces and the measured data.

A Comparison Study of foF2 Derived from Oblique Sounding Network and Vertical Ionosonde in Northern China

A Comparison Study of <i>f</i>oF2 Derived from Oblique Sounding Network and Vertical Ionosonde in Northern China

Modeling of HF propagation at high latitudes on the basis of IRI

The paper presents the results of comparison between the modeling calculations and ionograms of oblique sounding for high-latitude HF radio paths of Arctic and Antarctic Research Institute (AARI), which was fulfilled for February 13–14, 2014 (quiet conditions). The International Reference Ionosphere 2012 model of the ionosphere (IRI-2012) was used for the study. The comparison results prove that without adaptation to current diagnostics the IRI model does not reflect the real state of high latitude ionosphere even for quiet conditions. It was found that in general the observed maximum usable frequency values (MUF) exceeded the same values obtained from the model. The adaptation of the model to current diagnostics makes the simulated MUF values significantly closer to the observed MUF. The following parameters were used for the study: critical frequencies foF2 measured by ionosondes located near the considered paths, frequencies calculated on the basis of observed TEC values and median values of the equivalent slab thickness of the ionosphere.The relative error of calculation of MUF values averaged for all the cases for one hop was 23.6% by the initial IRI model. This error was decreased by 4% for the calculations on the basis of observed ТЕС and by 6% for the adaptation to foF2. The higher the latitude of the studied radio path, the more the difference between the observed and simulated MUF values. The conclusion was made that a principal cause of this difference was the deviation of calculated maximum ionospheric height values (hmF2) from the observed hmF2. The additional model update using hmF2 values obtained from Tromso station let to better match between the calculated MUF values and the observed MUF values for all radio paths. The analysis of experimental data showed that the non-predicted events (like traveling ionospheric disturbances, M- and N-modes, lateral modes, triplets, unusual scatter effects, etc.) sometimes took place at high latitude paths even during the quiet conditions.

ЭФФЕКТЫ СОЛНЕЧНОГО ЗАТМЕНИЯ 20 МАРТА 2015 Г. В ИОНОСФЕРЕ НАД ЕВРОПОЙ: РЕЗУЛЬТАТЫ ИОНОЗОНДОВЫХ НАБЛЮДЕНИЙ

ЭФФЕКТЫ СОЛНЕЧНОГО ЗАТМЕНИЯ 20 МАРТА 2015 Г. В ИОНОСФЕРЕ НАД ЕВРОПОЙ: РЕЗУЛЬТАТЫ ИОНОЗОНДОВЫХ НАБЛЮДЕНИЙ

Прогноз характеристик распространения декаметровых радиоволн на основе глобальной модели ионосферы и плазмосферы

We present the forecast results of maximal usable frequencies for mid-latitude paths on the base of complex We present the results of forecasting maximum usable frequencies (MUF) on middle-latitude paths on the basis of complex algorithm including modules of the ionosphere and plasmasphere global model (IPGM) and the model of radio wave propagation. The computation of propagation characteristics for decameter radio waves is carried out within the framework of normal wave technique. IPGM developed in ISTP SB RAS enables to compute electron concentration profiles and effective frequency of collisions using minimum number of input data and taking into account physical processes in the Earth’s upper atmosphere. To estimate the efficiency of using IPGM in long-term forecast of radio wave propagation we computed MUF for radio communication in various heliogeophysical conditions. To obtain precision characteristics of MUF forecast we used experimental data of oblique sounding on Magadan–Irkutsk, Khabarovsk–Irkutsk, Norilsk–Irkutsk paths. The paths are equipped with modern ionosphere diagnostic hardware for oblique sounding by continuous chirp signal. We also compared results of MUF forecast using IPGM with computations carried out according IRI model.

Vertical and oblique ionospheric soundings over the long haul HF link between Antarctica and Spain

AbstractThis paper presents a comparative study between the oblique sounding results, the International Telecommunication Union Rec533 HF prediction model, and the vertical sounding results of a transequatorial long haul link. The long haul link is a 12,760 km link between the Spanish Antarctic Station, SAS, located in the Livingston Island and the Ebro Observatory (OE) in Spain. The data were collected during three consecutive surveys (2009/2010, 2010/2011, and 2011/2012). The ionospheric channel from the SAS to the OE is studied in terms of frequency availability as function of time using the measurements of an oblique incidence sounder (OIS) and measurements of several vertical incidence sounding stations (VIS) placed near the estimated radiopropagation path. The results obtained show promising correlations between VIS and OIS measurements and led us to think that the frequency of largest availability for this particular long haul radio link can be estimated from the VIS sounding measurements.

Real-time automatic scaling method of oblique ionogram parameters based on morphological operator and inversion technique

Automatic scaling ionogram can get the parameters of ionogram which are vital to ionosphere detecting. In this paper, a new method is proposed to scale F2 layer trace automatically from oblique ionogram based on morphological operator and inversion technique. This method is verified through the comparison of actual detecting data with statistical analysis. The results show that the proposed automatic scaling method has high acceptable rate and is suitable for scaling oblique ionogram with different high angle wave states. It is fast and precise to fit O-mode echoes in F2 layer without the influence from F1 layer. This method could be applied in real-time ionospheric oblique sounding research with high reliability and versatility.

Determination of sporadic E radio wave propagation parameters based on vertical and oblique sounding

Sporadic E layer is often determined for HF radio communication. We have to deal with oblique radiowave propagation in the radio practice. The limiting frequencies at oblique propagation depend heavily on the transmitter power and the receiver sensitivity. The reason for this, as in the case of vertical propagation, is the dependence of Es reflection coefficient, ρEs (reflection loss R(dB)), on Es operation frequencies. This paper describes the characteristics of HF Es propagation in relation to foEs obtained from ionospheric vertical observations. It was found that characteristics of Es propagation depend on the type and height of the Es layer. Also the foEs diurnal variation at definite R(dB) was detected. This investigation allows improving the prediction of limiting frequencies for HF radio propagation.

Signal absorption effects on HF radio paths near Sodankyla observatory (Finland)

Studies were performed on three oblique ionospheric sounding (OIS) paths: Gor’kovskaya-Lovozero (St. Petersburg) with a length of 890 km, Sodankyla-Gor’kovskaya (800 km), and Sodankyla-Lovozero (360 km). The data for March 17 and April 14, 2012, the days during the recovery phase of the corresponding magnetic storms, have been analyzed. According to the observations performed at Sodankyla, riometer absorption in the morning-daytime hours was high against a background of very weak magnetic disturbances registered with a magnetometer; a high absorption level was also typical of the second day but during a substantial magnetic disturbance. The signal propagation mode structure and intensity on different paths were compared for the indicated days. The main results achieved are as follows. The OIS signal mode structure at weak (for April 14, 2012) and strong (for March 17, 2012) absorption substantially differed when magnetic disturbances were weak at the same instant. Diffuse reflections from the F2 layer were observed on the first two paths during a magnetic disturbance at night of April 14, 2012. At the same time, diffusivity was absent on the same paths under quiet magnetic conditions in the morning and daytime hours on March 17, 2012. A short-term abrupt increase in the maximum observed frequency of the Es layer (MOF Es) by 30–80% was registered half an hour before a substantial absorption burst on the first path. Signal reflections from the sporadic Es layer were observed only on the first path on March 17, 2012, and April 14, 2012, during the absorption maximum (A = 6 dB) according to the Sodankyla data, and the signal characteristics differed on those days.

Automatic interpretation of oblique ionograms

We present an algorithm for the identification of trace characteristics of oblique ionograms allowing determination of the Maximum Usable Frequency (MUF) for communication between the transmitter and receiver. The algorithm automatically detects and rejects poor quality ionograms. We performed an exploratory test of the algorithm using data from a campaign of oblique soundings between Rome, Italy (41.90 N, 12.48 E) and Chania, Greece (35.51 N, 24.01 E) and also between Kalkarindji, Australia (17.43 S, 130.81 E) and Culgoora, Australia (30.30 S, 149.55 E). The success of these tests demonstrates the applicability of the method to ionograms recorded by different ionosondes in various helio and geophysical conditions.

Client-server system mobile experiment control and data analysis with oblique ionospheric sounding

We propose an approach to solving the problem of mobile management and the analysis of data of oblique sounding of an ionosphere and ionospheric HF radio channels on a network of radio links. On the basis of our research, we have shown the way to solve this problem, illustrated by diagrams of client-server architectures, mobile client interface and a mobile system to interaction with the receiving terminal.

Numerical Simulation of the Influence of the may 2–3, 2010 Geomagnetic Storm on HF Radio-Wave Propagation in the Ionosphere

This study is devoted to HF radio wave propagation in the ionosphere during the May 1–3, 2010 geomagnetic storm. The research results were obtained by using two models, namely, the GSM TIP environment model developed at WD IZMIRAN and the radio-wave propagation model developed at I. Kant BFU. For certain selected frequencies we show the effect of the geomagnetic storm on the radio wave propagation. We give examples of a HF radio-wave path in the channels between the F1 and F2 layers of a high-latitude ionosphere and the F2 and F3 layers of a lowlatitude ionosphere. Characteristics of these layers may significantly affect the interpretation of the oblique sounding ionograms.

Modeling of high frequency radio wave absorption on oblique soundings during a solar X-ray flare

High frequency radio wave absorption induced by Solar Ultra-Violet (UV) and X-ray flux is investigated. The influence of the solar flare observed on 11 April 2013 on the structure of oblique sounding ionograms in the Arctic region of Russia is considered. An adjustable model of the ionosphere developed for high frequency (HF) propagation problems was employed for this purpose. The simulation algorithm has been designed to accept a large variety of ionospheric conditions. On the basis of the SWPC D-region Absorption model the absorption effects in the ionosphere at sub-auroral latitudes of the Earth were calculated. This approach does not require knowledge of the electron density and electron collision frequency profiles of the D-region ionosphere. The oblique ionograms simulated with the absorption effect and ionograms provided by Russian network of ionospheric observations deployed in Arctic region exhibit quite a good resemblance.

Ionospheric Effects of the X-Ray Flares of September 24, 2011 According to Oblique Sounding Data

UDC 550.388.2 We present the results of observations of a sudden wideband attenuation of short radio waves and Doppler-shift variations of the signals from broadcast stations on oblique sounding paths in the Eurasian longitudinal sector during a series of X-ray flares that occurred on September 24, 2011. The results of modeling of the electron-density profiles in the lower ionosphere based on measurements of attenuation of short waves on the Moscow — Rostov-on-Don path at a frequency of 9996 kHz of the standard-time RWM station during the most powerful flare that occurred on September 24, 2011 at 09:40 UT are given.

Inversion of Oblique Ionograms Based on Hybrid Genetic Algorithm

AbstractThe oblique sounding is a powerful tool for acquiring ionospheric information, and we can get the structural parameters related to ionosphere by inversing the oblique ionogram. Genetic algorithm (GA) is a widely used inversion method which can reduce the non‐uniqueness of the inversion problems without depending on the initial estimation, but the accuracy and reliability of GA's inversion results may be decreased due to “premature convergence” and inferior local search ability. So an improved hybrid genetic algorithm (HGA) based on simulated annealing algorithm (SA) is proposed and firstly applied to inversion of oblique ionogram. HGA combines the advantages of GA and SA together and makes full use of them, so it has a strong global search ability and local search ability. To verify the reliability and stability of HGA's inversion results, we firstly use GA, SA, and HGA to inversion of the synthetic oblique ionogram and compare the inversion results of the three algorithms, find that HGA's results are nearest to the real values and its needed iterations are also much smaller than others. The inversion results include the critical frequency, the height of maximum electron density and half‐thickness. Then, comparing the influences on inversion results by changing the population size and the total iterations, we find that the HGA effectively reduces the influences. Lastly, we use the three algorithms to invert the real ionograms and compare the inversion results with the vertical data in the midpoint of transmitting and receiving site. The results show that the stability and the searching optimal solution ability of HGA are obviously better than the GA and SA, and its inversion results are reliable, so HGA has strong referential significance and practical value for the inversion of real ionograms.

Method for determining the critical frequency and propagation factor at the path midpoint from maximum usable frequency and its propagation delay based on oblique sounder

提出了一种利用斜向探测F₂层最高可用频率及其对应时延反演传播路径中点临界频率<em>f</em>₀F₂和3000km传输因子<em>M</em>（3000）F₂的新方法.该方法从工程实用角度出发，利用射线传播理论直接反演得到临界频率和3000km传输因子.通过对长春-径阳和新乡-赤峰两条斜向探测链路中点电离层参数的反演分析，验证了方法的稳定性；利用反演结果与北京垂直探测数据对比，验证了方法的准确性；通过与Smith方法的对比，验证了方法的实用性.统计分析显示，此方法具有与Smith方法可比的精度，明显优于参考电离层模型给出的结果，其均方误差为0.48MHz，相对误差为10.50%；具有较好的稳定性，对不同距离的探测链路有较好的适应性，反演精度差异为0.03MHz；具有可操作性强，易于实现的特点.本研究成果可用于短波通信频率实时预报、动态频率管理及其相关领域.

Recovery of the Nonmonotonic Altitude Profile of the Plasma Frequency Based on the Ionospheric Oblique Sounding Data

We propose a method and an algorithm for recovery of the nonmonotonic altitude profile of the plasma frequency using the model data on oblique sounding of a spherically layered isotropic ionosphere in the piecewise-quasiparabolic approximation of the altitude profile of the electron number density. The algorithm has been tested with a fairly complex ionosphere model allowing for the E, F1 ,a ndF2 layers and the E–F1 interlayer valley. This method was used to recover the effective altitude profile of the plasma frequency at the midpoints of the Khabarovsk–Tory, Magadan–Tory, Norilsk–Tory, and Usolie–Tory paths from the experimental ionograms having a gap in the single-hop mode traces. Recovery of the altitude distribution of the electron number density from oblique ionospheric sounding data yields the main parameters of the ionosphere in a region away from the transmitter and the receiver where the vertical sounding tools are absent for some reasons. Formulation of the problem for a spherically layered isotropic ionosphere makes it necessary to solve a system of two integral equations for the distance between the corresponding points and a range–frequency characteristic (RFC). The desired quantities in this system of equations are the altitude profile of the plasma frequency and the frequency dependence of the arrival (exit) angle of the beam. For the monotonic profiles (without gaps in the RFC), the problem is correct and has a unique solution. For the nonmonotonic profiles (with gaps in the RFC), the problem becomes ill-posed since one RFC can satisfy a family of altitude profiles of the plasma frequency differing in depth of the valley in the profile. Even for the inhomogeneous paths with a nonmonotonic altitude distribution of the electron number density there is a family of media that are only weakly discernible in the oblique ionospheric sounding data [1]. The inverse problem of oblique ionospheric sounding has been studied by many authors. In [2], as the method of solution, the author suggested that the system of integral equations should be reduced to a system of linear equations by a piecewise-parabolic approximation of a monotonic altitude profile of the electron number density. The considered method was improved in [3, 4]. In this approach, the nonmonotonic profiles of the electron number density can be recovered by using a piecewise-parabolic approximation of the plasma frequency squared. This technique was used in the calculations in [5], but there only the accuracy of recovery of a monotonic profile of the electron number density was improved compared with the algorithm based on a piecewise-hyperbolic approximation. In the study [6] based on the oblique ionospheric sounding data, a method is proposed for recovery of the electron number density with small horizontal gradients using the solution of a system of integral equations, but again only for a monotonic altitude profile of the plasma

Short-Term Forecasting Method of Maximum Usable Frequency for HF Communication Based on Oblique Sounder

Based on oblique sounding system, a short-term forecasting method of maximum usable frequency for HF communication was presented. The method include four steps: firstly, maximum usable frequency of oblique sounding circuit was forecasted based on its sounding data; secondly, the critical frequency of sounding path midpoint was determined from the oblique sounding data and its forecast data by using ray-path theory; thirdly, the critical frequency was reconstructed for forecast circuit; in the end, maximum usable frequency for HF communication circuit was given. Using the oblique sounding data during March 2012, the accuracy and practicability of the method was validated. The root-mean-square error of the short-term forecast is 1.56 MHz, and is reduced 0.40MHz contrast to that of the long-term prediction. The research provides the important reference for frequency selection and frequency management of HF communication.

Spread-F Radar Observations in the Midlatitude Ionosphere Using an Ionosonde–Radiodirection Finder

We present the results of experimental studies of the spread-F phenomenon in the midlatitude ionosphere, which were obtained using a broadband chirp HF radar of bistatic configuration on the Cyprus—Rostov-on-Don oblique sounding path. In the evening, night, and early morning hours of the winter and spring months, in a quiet geomagnetic environment, scattered signals were detected at frequencies exceeding the maximum observable frequency (MOF) of the directsignal 1F mode with the following parameters: delays of 6‐7.5 to 8.5‐11 ms, frequencies of 10‐14 to 13‐19 MHz, vertical angles of arrival of 20 ◦ to 45 ◦ , azimuthal angles of arrival of −30 ◦ to 50 ◦ , and amplitude of scattered signal by 70‐80 dB less than the direct-signal amplitude. Based on modeling of HF propagation and scattering and on comparison with the experimental data, it is established that the observable anormalous signal is due to the backscattering of radio waves by small-scale irregularities with sizes about 8‐10 m, which occupy an extended area of the midlatitude ionosphere (50 ◦ ‐55 ◦ N, 35 ◦ ‐48 ◦ E) at altitudes both below and above the F-layer maximum (250‐450 km). Relative fluctuations of the electron number density of the scattering irregularities are estimated as δN ≈ 7.8 · 10 −3 , which is about a factor of 3 to 5 greater than δN for natural fluctuations of the electron number density under typical conditions in the midlatitude ionospheric F region. Possible relation between spread F and the traveling ionospheric disturbances is discussed.