Oblique Sounding Research Articles

APPLICATION OF OBLIQUE IONOSPHERIC SOUNDING TO INCREASE THE ACCURACY CHARACTERISTICS OF THE OVER-THE-HORIZON RADAR

The over-the-horizon radar stations of the space wave are sensitive to changes in the ionosphere. For the accurate operation of such radars, it is necessary to have up-to-date information on the ionosphere at the reflection point of radio waves. The article gives an example of the implementation of a network of ionospheric stations working in the interests of the FG of the radar station with the example of the Australian system JORN. It is proposed to use the Russian vertical ionosondes Parus-A for ionospheric support of the radar. These ionosondes are also capable of performing oblique sounding at distances up to 2000 km. The results of oblique sounding by these ionosondes are shown on various routes on the territory of Russia: in the European part of the country, in Siberia and in the Far East. The features are explained and the analysis of the data is carried out. It is concluded that the problem is topical and that it can be solved. The potential is shown in the ionosonde Parus-A at the development stage and implemented later.

Oblique Ionograms Automatic Scaling Algorithm OIASA application to the ionograms recorded by Ebro observatory ionosonde

The oblique ionograms automatic scaling algorithm (OIASA), developed at the INGV for the identification of trace of oblique ionograms, allows the determination of the maximum usable frequency (MUF) for communication between the transmitter and receiver, automatically rejecting poor quality ionograms. A test of the algorithm using data from a campaign of oblique soundings between Dourbes (50.1°N, 4.6°E) and Roquetes (40.8°N, 0.5°E) has been performed. Oblique soundings from three different campaigns have been studied, covering different geomagnetic conditions, in order to study the behavior of the autoscaling algorithm under quiet and perturbed geomagnetic periods. The reported results demonstrate that OIASA performance is not influenced by geomagnetic or ionospheric activity conditions. This demonstrates a satisfactory performance of the automatic scaling algorithm, even under different geomagnetic conditions, the potential application of OIASA as a near-real-time tool for ionospheric monitoring purposes, and its performance for tracking ionospheric effects caused by space weather events.

Ionosphere disturbance during cosmodrome “Vostochniy” launches

It is known that during spacecraft launches ionospheric plasma properties are modified in the result of impact of shock-acoustic waves generated during carrier rocket supersonic motion. As a rule, investigation of ionospheric plasma variations is carried out by the signals of Global Navigation Satellite Systems GPS/GLONASS that implies ground station network. There is no such a system near the “Vostochniy” cosmodrome that makes it necessary to search for an alternative solution. One of them may be the application of ionosphere vertical and oblique sounding stations. Based on the analysis of such station data, the possibility of evaluation of ionosphere modification during “Vostochniy” cosmodrome launches is shown.

Sporadic E S Layers at High Latitudes During a Magnetic Storm of March 17, 2015 According to the Vertical and Oblique Ionospheric Sounding Data

We consider the behavior of the parameters of the ionospheric E s layers according to the vertical sounding at the Sodankyla observatory and oblique sounding at the Lovozero (Murmansk region)—Gor’kovskaya station (Leningrad region) path during a superstorm of March 17, 2015. Temporal and spatial behavior of these parameters is compared. It was found that the storm significantly distorted the normal course of variations of the sporadic E s layer characteristics. Specific behavior of the layers during a storm at points separated by about 300 km was detected. With the help of ray tracing calculations using the IRI model, oblique sounding ionograms were constructed for the radio path analyzed. Primary attention is given to the maximum usable frequency of the F 2 layer—MUF-F 2. Additionally, for the disturbed conditions where there is only a high-power E s layer on the experimental ionograms, the values of MUF-E s and the ratio K =MUF-E s/f o E s for various cutoff frequencies f o E s of the E s layer and its altitudes $$ {h}_{E_s} $$ are calculated within the framework of the well-known approximations. Calculations for the case of weak disturbance and semitransparent E s layers are carried out with the IRI model adapted to the current diagnostics parameters. It was found that the calculated and experimental values of MUF-F 2 are close to each other or coincide, while this cannot be said about MUF-E s. The calculated and experimental values of MUF-E s can be matched in the model of mirror reflection from a flat layer for intense layers and the model of the E layer for thick E s layers of low intensity.

Impact of a Strong Magnetic Storm and Two X-Ray Flares on the Ionospheric HF Channel in the Summer Solstice of 2015 According to Oblique Sounding in the Eurasian Region

We present the results of observations of the impact a strong magnetic storm and two X-ray flares in the summer solstice of 2015 on the HF signal characteristics during oblique sounding of the ionosphere in the Eurasian region. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, up to a long blackout on the paths adjacent to the subauroral latitudes. On the midlatitude paths, a decrease in the maximum observable frequency of the F layer reached 50% with respect to the average values for an undisturbed ionosphere. The propagation velocity of the negative phase of a disturbance from the subauroral to the midlatitude ionosphere is determined (it is equal to about 100 m/s). It is shown that during a magnetic storm the least observable frequency and the average signal-to-noise ratio for the propagation mode via the sporadic E s layer correlate well with the auroral AE index. Anomalous signals were detected in the main phase of the magnetic storm on the Cyprus—Rostov-on-Don path when a chirp ionosonde–radio direction finder was operated in the over-the-horizon HF radar mode. On the basis of modeling and comparison with experimental data, it is shown that the anomalous signals are due to scattering of radio waves by small-scale irregularities located in the subauroral ionospheric F region.

Forecasting the conditions of the decameter radio wave propagation in the Аrctic region

In this paper we present the results of studies the distinctive features of the decameter radio wave propagation based on the results of experimental measurements of radio wave propagation characteristics by the ionospheric oblique sounding (IOS) method and numerical simulation. An algorithm for numerical modeling the trajectory and energetic characteristics of the decameter radio wave propagation in the framework of geometric optics is described. The agreement between the simulated and experimental radio propagation parameters (for example, the values of the maximum observed frequencies) is demonstrated. It is proposed to use the developed diagnostic model of the HF radio channel for the purposes of forecasting in areas not provided with IOS stations.

The lower ionosphere response to its disturbances by powerful radio waves

The paper presents data from some campaigns at Sura heating facility in 2011–1016. The experiments on probing of the artificial disturbed region of the lower ionosphere were carried out at two observation sites. One of them was located near Vasil’sursk 1km from Sura facility (56.1°N; 46.1°E) and the other site was located at the Observatory (55.85°N; 48.8°E) of Kazan State University, 170km to the East. Investigation of the features of the disturbed region of the lower ionosphere based on its diagnostics by the methods of the vertical sounding and oblique backscattering is the main goal of this paper. Ionosphere disturbance was fulfilled by the effect of the powerful radio wave of the ordinary or extraordinary polarization emitted by transmitters of the Sura facility with effective radiated power ERP=50–120MW at the frequency of 4.3, 4.7 and 5.6MHz. Pumping waves were emitted with period from 30s to 15min. The disturbed region of the ionosphere in Vasil’sursk was probed by the vertical sounding technique using the partial reflexion radar at the frequency of 2.95 and 4.7MHz. For the oblique sounding of the disturbed region the modified ionosonde Cyclon-M, operating at ten frequencies from 2.01 to 6.51MHz was used at the Observatory site. On many heating sessions simultaneous variations of the probing partial reflection signals in Vasil’sursk and backscattered signals in Observatory were observed at the height at 40–100km below the reflection height of the pumping wave. These observations were correlated with the pumping periods of the Sura facility. Possible mechanisms of the appearance of the disturbance in the lower ionosphere and its effect on the probing radio waves are discussed.

Impact of heliogeophysical disturbances on ionospheric HF channels

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ∼50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (∼100m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero – Yoshkar-Ola and Cyprus – Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus – Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval.

About Factors of Solar Radiation Affecting the Ionosphere

AbstractIn this report we present an attempt to find a characteristic set of the space weather parameters allowed to identify the dominant physical connections. This study is based on the data of vertical and oblique sounding of the ionosphere in 2015-2016.

Vertical and oblique ionospheric soundings performance comparison over the 12,760 km transequatorial HF link between Antarctica and Spain

AbstractThis paper presents the second part of the study of the oblique sounding of a 12,760 km transequatorial ionospheric link between Livingston Island (Antarctica) and Cambrils in Spain. The study consists of the comparison among the oblique sounding results using an inverted V as receiver antenna, the International Telecommunication Union Rec533 HF prediction model, and the vertical sounding results on the path of the long haul channel. The data were collected the last consecutive surveys, when the inverted V antenna was operative (2010–2011, 2011–2012, 2012–2013, and 2013–2014). The ionospheric channel is studied in terms of frequency availability depending on time using the measurements of an oblique incidence sounder (OIS) and also measurements of several vertical incidence sounding stations (VIS) on the path of the long haul channel. The results obtained show similarities between the VIS and the OIS measurements; following previous studies preliminary results, the experiments conducted led us to think that the frequency of large availability can be estimated depending on the VIS sounding results.

Oblique Sounding of the Ionosphere by Means of an Ionosonde–Direction Finder with Chirp Signal

We give a mathematical rationale, an algorithm, and hardware implementation for a multichannel ionosonde–direction finder with chirp signal. The results of experimental studies of twodimensional angle–frequency characteristics on the Cyprus—Rostov-on-Don meridional obliquesounding path are presented. It is shown that both regular (terminator-related) and irregular (caused by the passage of a traveling ionospheric disturbance through the propagation path) transverse (with respect to the propagation path) horizontal gradients of the electron number density lead to a deviation of the azimuth of the high-angle ray in the direction of the Ne gradient. The experimental data are compared with the simulation results.

Modeling z-shaped disturbance along the Pedersen ray of oblique sounding ionogram using adaptation of IRI to experimental data

We present the results of numerical modeling of a traveling ionospheric disturbance that causes z-shaped bends at the Pedersen ray of oblique incidence ionograms. The results of trajectory synthesis of oblique incidence ionograms are given for the ionosphere, taking into account the traveling ionospheric disturbance. In the work, we use the International Reference Ionosphere, adapted to experimental data, and the Global Model of the Ionosphere and Plasmasphere.

Исследование пространственной структуры искусственной ионосферной турбулентности с помощью техники наклонного зондирования

Исследование пространственной структуры искусственной ионосферной турбулентности с помощью техники наклонного зондирования

An automatic scaling method for obtaining the trace and parameters from oblique ionogram based on hybrid genetic algorithm

AbstractScaling oblique ionogram plays an important role in obtaining ionospheric structure at the midpoint of oblique sounding path. The paper proposed an automatic scaling method to extract the trace and parameters of oblique ionogram based on hybrid genetic algorithm (HGA). The extracted 10 parameters come from F2 layer and Es layer, such as maximum observation frequency, critical frequency, and virtual height. The method adopts quasi‐parabolic (QP) model to describe F2 layer's electron density profile that is used to synthesize trace. And it utilizes secant theorem, Martyn's equivalent path theorem, image processing technology, and echoes' characteristics to determine seven parameters' best fit values, and three parameter's initial values in QP model to set up their searching spaces which are the needed input data of HGA. Then HGA searches the three parameters' best fit values from their searching spaces based on the fitness between the synthesized trace and the real trace. In order to verify the performance of the method, 240 oblique ionograms are scaled and their results are compared with manual scaling results and the inversion results of the corresponding vertical ionograms. The comparison results show that the scaling results are accurate or at least adequate 60–90% of the time.

Ionospheric Effects of a Solar Eclipse of March 20, 2015 on Oblique Sounding Paths in the Eurasian Longitudinal Sector

The results of measuring HF signals on oblique chirp sounding paths in the Eurasian region during a solar eclipse of March 20, 2015 and the neighboring days are presented. The solar eclipse took place against the background of a strong magnetic storm. It was established that during the solar eclipse on oblique sounding paths of different length and orientation the decrease in the maximum observable frequency for the F mode (MOF-F) and the lowest observable frequency for the F mode (LOF-F) was 8–14% and 22–33%, respectively. During the eclipse, the signal amplitude increased by 3–5 dB. On the Lovozero—Nizhny Novgorod path in the maximum phase of the solar eclipse, the electron density decrease in the ionospheric E and F2 layers at the midpoint of the path reached 37% and 22%, respectively. According to the MOF and LOF variation measurements for various modes, the group delay time of radio signals, and the results of spectral analysis, it was found that in the eclipse there were wave disturbances with a period of 25 to 50 min. However, quasi-periodic variations of MOF-F and LOF-F having a a period of 50 to 80 min but which started before the eclipse were detected on some paths. Probably, in these cases, the variations were a result of the superposition of disturbances from two sources, namely, the magnetic storm and the solar eclipse.

Anomalous phenomena on HF radio paths during geomagnetic disturbances

We analyze ionospheric oblique sounding data on three high-latitude and one high-latitude–midlatitude HF radio paths for February 15 and 16, 2014, when two substorms and one magnetic storm occurred. We investigate cases of anomalous propagation of signals: their reflection from sporadic layer Es, lateral reflections, type “M” or “N” modes, the presence of traveling ionospheric disturbances, and the diffusivity of signals and triplets. The most significant results are the following. In geomagnetically undisturbed times, sporadic Es-layers with reduced maximum observed frequencies (MOFEs) on three high-latitude paths were observed in both days. The values of MOFEs during disturbances are large, which leads to the screening of other oblique sounding signals reflected from the ionosphere. On all four paths, the most frequently traveling ionospheric disturbances due to the terminator were observed in quiet hours from 03:00 to 15:00 UT on the first day and from 06:00 to 13:00 UT on the second day of the experiment. In addition, both the sunset terminator and the magnetic storm on the high-latitude–mid-latitude path were found to generate traveling ionospheric disturbances jointly. No such phenomenon was found on high-latitude paths.

The investigation of ionospheric response to total eclipses on 29th March, 2006 and on 20th March, 2015 based on HF oblique sounding data

The investigation of ionosphere response to solar eclipses was carried out. Maximum observable frequencies were analyzed during two eclipses on 29th March, 2006 and on 20th March, 2015 on several oblique sounding paths which were within the range of solar flux obscuration. The model describing local changes in the ionosphere, caused by the obscuration of solar flux during eclipse, is suggested. The computer simulation of HF radiowave propagation during the eclipses was carried out on the basis of this model, while quiet ionosphere was described by IRI-2012 model. It is shown that this approach gives adequate description of HF channel during eclipses for all propagation paths under consideration while the parameters of the model were the same for all paths. As the result of computer simulation time delays of ionosperic responses during eclipses were obtained (~1800–2000s). It was found that maximum depletion of electron concentration reached 85% in D-region for both eclipses. The electron density depletions at height of F2-peak were 48% and 34% for eclipse on 29th March, 2006 and on 20th March, 2015 respectively.

Multi-quasi-parabolic ionosphere model with EF-valley

<p>We improve the conventional multi-quasi-parabolic (MQP) model and develop two MQP models with EF-valley by applying the predicted EF-valley parameter of the newest version of the International Reference Ionosphere. On the basis of the conventional MQP model and these two improved MQP models with EF-valley, we generate one-hop oblique sounding ionograms between Wuhan and Beijing. Comparisons between the generated ionograms and the sounding ionogram in the experiments illustrate that the improved MQP models are more suitable for describing the true ionosphere than the conventional MQP model is. In contrast to the conventional MQP model, the improved MQP models can increase the accuracy of ray tracing and reduce the errors in shortwave single location and over-the-horizon-radar registration.</p>

Physical Layer Definition for a Long-Haul HF Antarctica to Spain Radio Link

La Salle and the Observatori de l’Ebre (OE) have been involved in a remote sensing project in Antarctica for the last 11 years. The OE has been monitoring the geomagnetic activity for more than twenty years and also the ionospheric activity of the last ten years in the Spanish Antarctic Station Juan Carlos I (ASJI) (62.7 ° S, 299.6 ° E). La Salle is finishing the design and testing of a low-power communication system between the ASJI and Cambrils (41.0 ° N, 1.0 ° E) with a double goal: (i) the transmission of data from the sensors located at the ASJI and (ii) the performance of an oblique ionospheric sounding of a 12,760 km HF link. Previously, La Salle has already performed sounding and modulation tests to describe the channel performance in terms of availability, Signal-to-Noise Ratio (SNR), Doppler spread and delay spread. This paper closes the design of the physical layer, by means of the channel error study and the synchronization performance, and concludes with a new physical layer proposal for the Oblique Ionosphere Sounder. Narrowband and wideband frames have been defined to be used when the oblique sounder performs as an ionospheric sensor. Finally, two transmission modes have been defined for the modem performance: the High Robustness Mode (HRM) for low SNR hours and the High Throughput Mode (HTM) for the high SNR hours.

A procedure for the reliability improvement of the oblique ionograms automatic scaling algorithm

AbstractA procedure made by the combined use of the Oblique Ionogram Automatic Scaling Algorithm (OIASA) and Autoscala program is presented. Using Martyn's equivalent path theorem, 384 oblique soundings from a high‐quality data set have been converted into vertical ionograms and analyzed by Autoscala program. The ionograms pertain to the radio link between Curtin W.A. (CUR) and Alice Springs N.T. (MTE), Australia, geographical coordinates (17.60°S; 123.82°E) and (23.52°S; 133.68°E), respectively. The critical frequency foF2 values extracted from the converted vertical ionograms by Autoscala were then compared with the foF2 values derived from the maximum usable frequencies (MUFs) provided by OIASA. A quality factor Q for the MUF values autoscaled by OIASA has been identified. Q represents the difference between the foF2 value scaled by Autoscala from the converted vertical ionogram and the foF2 value obtained applying the secant law to the MUF provided by OIASA. Using the receiver operating characteristic curve, an appropriate threshold level Qt was chosen for Q to improve the performance of OIASA.