Oblique Ionospheric Sounding Research Articles

Ionosonde antenna system for combined ionospheric sounding

The article is devoted to new and promising directions of development of ionosonde antenna systems, which have appeared in recent years and are able to conduct vertical and oblique sounding of ionosphere. A brief historical overview of ionosphere research has been given. The principles of vertical sounding of ionosphere and formation of ionograms in the frequency range from 1 to 30 MHz have been considered. The most widespread ionosondes of Russia and the world (DPS-4 (USA), CADI (Canada), Parus-A, Tomion, Raduga) have been studied. The analysis of antenna systems of these ionosondes (delta antennas, large and small rhombus antennas, etc.), their designs, directional patterns, conditions of application has been carried out. Proposals for modernizing the antennas, which have been put forward by foreign and Russian scientists, have been reviewed. A proposal to create a new, original design of the antenna system for combined sounding of the ionosphere has been given. The presented results create a basis for modernization and industrial production of promising antenna arrays.

Influence of helio-geophysical activity on reliability of short-wave communication in transport

The results of studies of the influence of coronal mass ejections and high-velocity solar wind streams on the characteristics of the ionosphere are presented. The analysis uses ionospheric data from the CADI vertical sounding station (Vasilsursk, Nizhny Novgorod region) and data from chirp stations for oblique ionospheric sounding on different paths of the Eurasian region of Russia: three subauroral (Lovozero-Vasilsursk, Sodankyulya-Vasilsursk and Salekhard-Vasilsursk) and one mid-latitude (Gorky, Leningrad region-Vasilsursk). A set of space weather parameters (type and speed of coronal mass ejections, high-speed solar wind speed) is considered, which made it possible to reveal the dominant physical relationships between the ionospheric dynamics and these two solar phenomena, which determine the reliability of short-wave radio communication between ships and the coast, especially in the area of the northern sea way.

Russian High-latitude Network of Oblique Ionospheric Sounding

Russian High-latitude Network of Oblique Ionospheric Sounding

РОССИЙСКАЯ ВЫСОКОШИРОТНАЯ СЕТЬ НАКЛОННОГО ЗОНДИРОВАНИЯ ИОНОСФЕРЫ

The network for monitoring the high-latitude ionosphere by the method of oblique ionospheric sounding deployed in the Russian Arctic region is considered. The study describes the main results of operational data processing for studying the high-latitude ionosphere and determining the conditions for the optimum operation of radio communication systems and over-the-horizon radars in this region. The study demonstrates the potential of the network as a tool for the remote diagnostics of parameters of small-scale artificial ionospheric irregularities induced by powerful HF radio waves in the mid-latitude ionospheric F-region.

Substorm Manifestations at Radio Paths of Oblique Ionospheric Sounding in the Arctic

The impact of geomagnetic substorms on radio propagation within the high-frequency (HF) range was analyzed using oblique ionospheric sounding data. These data were obtained from the unique system of radio paths that covers the whole region of the Russian Arctic. The study focused on the effects of two substorms with a twofold difference in intensity. Variations of four radio propagation parameters were studied: the maximum and lowest observed frequencies of the F2 ionospheric layer (F2MOF and F2LOF), and the same frequencies of the sporadic Es layer (EsMOF and EsLOF). Even the weak geomagnetic substorm (AEmax ~ 500 nT) significantly changed the ionosphere state and, consequently, the character of radio propagation at paths. The absorption of signals was more pronounced during a more intense substorm which resulted in loss of information during the transmissions through HF channels. The variations of propagation parameters (ΔMOF and ΔLOF) depend more on the path reflection point location and on the intensity of a substorm. Two substorms with a twofold difference in intensity had similar effects on ΔMOF, except for (a) the more pronounced smoothing of the Main Effect and (b) the higher ΔEsMOF amplitude during the intense substorm. Both issues are explained by more intense particle precipitations during the more intense disturbance.

Features of High-Frequency Radio Wave Propagation on Auroral Paths at Different Geomagnetic Activity

Variations in the parameters of the propagation of decameter waves on two auroral radio paths, Dikson–Pevek (D = 2800 km) and Lovozero–Pevek (D = 4200 km), were studied via oblique ionospheric sounding for two days, one weakly disturbed and one strongly disturbed. The following parameters were analyzed: F2 MOF and Es MOF (the maximum observed frequencies when the signal is reflected from the F2 layer and the Es layer), F2Spread (diffuse reflection), and lateral reflections. The following new results have been obtained: the F2 MOF level for the strongly disturbed day is higher than that for the weakly disturbed day on both paths; however, the F2 MOF values during substorms are either small or absent due to increased absorption. The Es MOF values on the Dikson–Pevek path increase during the period of disturbances. As for the Lovozero–Pevek path, the probability of Es reflections decreases during the disturbed day. The diffusion in the F2 layer on the Dikson–Pevek path is mostly typical for a strongly disturbed period, while that on the Lovozero–Pevek path, conversely, is mostly typical for weakly disturbed conditions. Lateral reflections on the Dikson–Pevek path occur rather rarely. On the Lovozero–Pevek path, there are very few lateral reflections on the weakly disturbed day and no lateral reflections on the strongly disturbed day.

Frequency Dependence of the Wave Field Power Parameters for Limiting Single-Hop Radio Paths in Low Solar Activity Conditions

This paper considers the possibility of the deep trough formation in the integral amplitude–frequency dependence of the wave field at the classical limiting paths of a single-hop ionospheric radio waves propagation under conditions of low solar activity. Calculations based on the global ionospheric model with both standard (IRI) and alternative dynamic (IRI + GDMF2) representations of the F2 layer of the ionosphere are compared with the experimental results of multifrequency oblique ionospheric sounding (OIS). It is shown that it is fundamentally possible to use the model to describe this feature based on the energy parameters of the radiation transfer problem in the ionosphere.

Observed and Calculated Ionograms of Oblique Ionospheric Sounding on HF Radio Paths During a Magnetic Storm of September 7–8, 2017

Ionograms of the oblique ionospheric sounding radio paths Cyprus—Lovozero and Lovozero—Gor’kovskaya (near St. Petersburg) are analyzed using magnetometers and riometers. The behavior of the maximum observed frequencies (MOF) of the F2 and Es layers during a magnetic storm of September 7–8, 2017 is considered. The storm has a specific, not classical form and can be divided into two parts, namely, the first and the second storms. The main results are as follows. 1) The manifestation of the first storm is accompanied by a significant increase in absorption and frequent absence of signals on the paths. The second storm is characterized by increased values of MOF-Es and the presence of signals. 2) The signals on the midlatitude Cyprus—Lovozero path propagate both as 1F2, 2F2, and 3F2 modes and as 2Es and 3Es modes. 3) On the subpolar Lovozero—Gor’kovskaya path, during the disturbance, the signals mainly propagate via reflection from the sporadic Es layer of very high intensity. 4) Modeling of the propagation of HF radio waves using the IRI-2016 model adapted to the vertical sounding data made it possible to match the model ionograms with the real oblique sounding ionograms, including the cases of presence of the M and N modes, as well as triplets, in both quiet and disturbed conditions, which is a new result.

First observations of oblique ionospheric sounding chirp signal in Mexico

Abstract The results of the first experiment of oblique ionospheric sounding (OIS) chirp signal reception in Mexico are reported. Maximal and Lowest Observed Frequencies variations were studied under the quiet Space Weather conditions. The diurnal ionospheric variations by OIS signal confirm the results based on GNSS data in the Mexican region. The best HF radio propagation conditions along the considered path are during morning and daytime hours. The multi-hop propagation is frequent. The interlayer propagation modes are present at nighttime.

Impact of geomagnetic storm of September 7–8, 2017 on ionosphere and HF propagation: A multi-instrument study

The present study reveals the features of ionospheric parameters variations during the geomagnetic storm of September 7–8, 2017. In particular, parameters of vertical (foF2, foEs) and oblique ionospheric sounding (MOF, modes), absorption level, Total Electron Content (TEC) and particle fluxes at high altitudes were under analysis. The storm was characterized by two Dst-index mimima and can be considered as a sequence of two storms: first - with Dstmin = −142 nT at 02 UT on September 8th and second - with Dstmin = −122 nT and at 15 UT on September 8th. It was found that these two storms had different impacts on the ionosphere and HF propagation at mid- and high-latitudes of Northern Hemisphere. The signals of vertical and oblique ionospheric sounding were present in all ionograms before the first storm. Further, at the maximum of the first storm these signals were totally absorbed. Then, before the second storm and during its maximum the signals were detected again in the ionograms due to the low absorption. GOES satellite data showed the significant burst of electrons and protons only during the first storm and small particle fluxes - during the second storm. This feature was also confirmed with GPS data: TEC increased during the first storm and decreased during the second storm.

Use of Hazard Function for Signal Detection on Ionograms

This letter considers a new method for sample detection of ionospheric propagation modes at the receiver output of a chirp ionosonde. The method is based on the use of the hazard function. Within the framework of the two-component mixture model, it is shown that the hazard function can be used to detect samples of the second component in the mixture when the corresponding fraction of samples in the total number is small. The implementation of the method is carried out using training sets. An average normalized hazard function is constructed for the training set not containing the signal. Normalization is carried out in such a way that the hazard function can be considered as a probability density function of a certain random variable. We used Pearson’s statistic to test the agreement between the average normalized hazard function of samples that do not contain the signal and an arbitrary normalized hazard function. The critical value of the statistic was determined using the Neyman–Pearson criterion. The effectiveness of the proposed method has been tested for the determination of the lowest and maximum observed frequencies of radio paths from oblique ionospheric sounding ionograms obtained in the Russian network of circumpolar radio paths. The method suggested in this letter can be used not only when processing ionograms but also for the detection of samples of signals of arbitrary nature against a background noise, provided that statistical signal-to-noise ratios are similar to those considered here.

Separation of O/X Polarization Modes on Oblique Ionospheric Soundings

AbstractThe oblique‐incidence sounder (OIS) is a well‐established instrument for determining the state of the ionosphere, with several advantages over vertical‐incidence sounders (VIS). However, the processing and interpretation of OIS ionograms is more complicated than that of VIS ionograms. Due to the Earth's magnetic field, the ionosphere is birefringent at radio frequencies and a VIS or OIS will typically see two distinct ionospheric returns, known as the O and X modes. The separation of these two modes on a VIS, using a polarimetric receive antenna, is a well‐established technique. However, this process is more complicated on an OIS due to a variable separation in the phase difference between the two modes, as measured between the two arms of a polarimetric antenna. Using a polarimetric antenna that can be rotated and tilted, we show that this variation in phase separation within an ionogram is caused by the variation in incidence angle, with some configurations leading to greater variation in phase separation. We then develop an algorithm for separating O and X modes in oblique ionograms that can account for the variation in phase separation, and we demonstrate successful separation even in relatively difficult cases. The variation in phase separation can also be exploited to estimate the incident elevation, a technique which may be useful for other applications of HF radio.

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.

Features of backscatter ionospheric sounding as studied with a chirp ionosonde

We present the results of the studies of backscatter ionospheric sounding (BS) on the basis of a multipurpose chirp ionosonde developed in ISTP SB RAS. We analyze BS experimental data obtained during different seasons from 2005 to 2009. The accumulated dataset allows us to investigate features of BS signal propagation in various heliogeophysical conditions. To analyze and interpret BS signals on ionograms, we use the results of modeling of characteristics for chirp signals in the backscatter and oblique ionospheric sounding under a waveguide approach. We have revealed the most characteristic types of ionograms and have established conditions of appearance of a given type depending on the time of day, season, sounding direction, and medium conditions. In winter, spring, and autumn, the prevailing types of ionograms are those with BS signals corresponding to the propagation mode through reflection from the F layer. Signals reflected by E or Es layers are recorded during summer periods. At the same time, frequencies of the received signals are sufficiently large, and sometimes there are no reflections from the F layer.

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.

Исследование особенностей возвратно-наклонного зондирования ионосферы на базе ЛЧМ-ионозонда

We present the results of studies of backscatter ionospheric sounding (BS) on the basis of a multipurpose chirp ionosonde developed in ISTP SB RAS. We analyze BS experimental data obtained during different seasons from 2005 to 2009. The accumulated dataset allows us to investigate features of BS signal propagation in various heliogeophysical conditions. To analyze and interpret BS signals on ionograms, we use the results of modeling of characteristics for chirp signals in the backscatter and oblique ionospheric sounding under the waveguide approach. We have revealed the most characteristic types of ionograms and have established conditions of appearance of a given type depending on the time of day, season, sounding direction, and medium conditions. In winter, spring, and autumn, the prevailing types of ionograms are those with BS signals corresponding to the propagation mode through reflection from the F layer. Signals reflected by E or Es layers are recorded during summer periods. At the same time, frequencies of the received signals are sufficiently large, and sometimes there are no reflections from the F layer.

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.

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.

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.

Impact of the magnetic superstorm on March 17–19, 2015 on subpolar HF radio paths: Experiment and modeling

The ionospheric phenomena which significantly influenced radio propagation during March 17–19, 2015 are considered in the study. The data of oblique ionospheric sounding (OIS) were analyzed at six radio paths. These paths are located in the zone of North Siberia in Russia and have different lengths: from 1000 to 5000km. The results are the following. The magnetic storm drastically changed the character of radio propagation at all the considered paths: in most cases the reflections from the ionospheric F2-layer were changed by the reflections only from the sporadic Es-layer. The parameters of movement of the disturbance front were estimated on the basis of OIS data of the paths. The average velocity of the front movements from east to west was about V=440m/s. Even the moderate growth of riometer absorption within the region of radio paths’ locations, resulted in loss of multihop modes in the signal reflections from sporadic layers. It also resulted in a sharp decrease of signal strength at the paths. Real distance–frequency characteristics (DFC) of the paths were compared to DFC calculated on the basis of International Reference Ionosphere (IRI) model. It was revealed that on a quiet day of March, 15th, the real and the calculated DFC are similar or coincide in the majority of cases. During the disturbed days of March, 17–19, most commonly observed are the significant differences between the calculated and the experimental data. The most pronounced difference is revealed while estimating the character of OIS signals’ reflections from Es-layers.