On 3 November 2021, an interplanetary coronal mass ejection impacted the Earth’s magnetosphere leading to a relevant geomagnetic storm (Kp = 8-), the most intense event that occurred so far during the rising phase of solar cycle 25. This work presents the state of the solar wind before and during the geomagnetic storm, as well as the response of the plasmasphere–ionosphere–thermosphere system in the European sector. To investigate the longitudinal differences, the ionosphere–thermosphere response of the American sector was also analyzed. The plasmasphere dynamics was investigated through field line resonances detected at the European quasi-Meridional Magnetometer Array, while the ionosphere was investigated through the combined use of ionospheric parameters (mainly the critical frequency of the F2 layer, foF2) from ionosondes and Total Electron Content (TEC) obtained from Global Navigation Satellite System receivers at four locations in the European sector, and at three locations in the American one. An original method was used to retrieve aeronomic parameters from observed electron concentration in the ionospheric F region. During the analyzed interval, the plasmasphere, originally in a state of saturation, was eroded up to two Earth’s radii, and only partially recovered after the main phase of the storm. The possible formation of a drainage plume is also observed. We observed variations in the ionospheric parameters with negative and positive phase and reported longitudinal and latitudinal dependence of storm features in the European sector. The relative behavior between foF2 and TEC data is also discussed in order to speculate about the possible role of the topside ionosphere and plasmasphere response at the investigated European site. The American sector analysis revealed negative storm signatures in electron concentration at the F2 region. Neutral composition and temperature changes are shown to be the main reason for the observed decrease of electron concentration in the American sector.

In this paper, modified analytical equations for the total electric field intensity in the far field region of a 10 MHz bent wire antenna have been proposed. The antenna system is meant for the airborne ground penetrating RADAR application for bedrock survey. This bent antenna is having vertical, slant and horizontal segments joined together along with the parasitic element. The current in the antenna wire is assumed to be a sinusoidal distribution which drops to zero at the ends. Current in both the energized and parasitic elements contribute to the fields in the far field region of the antenna system. Separate field equations for the various segments of the antenna system have been derived and finally summed to obtain the required equation for the electric field intensity at the far field region of the antenna. The MATLAB R2017b© simulation results of the far field antenna analytical equations show good agreement with the HFSS© simulation results of the 10 MHz antenna system. Direct measurements of these radiation characteristics in a typical GPR environment present a lot of practical difficulties. In this work, the influence of the helicopter on the 10 MHz GPR antenna during the airborne survey, is simulated using EMPro© and analyzed. This placement analysis resuls from the simulation gives us the appropriate range of distance values that can be maintained between the helicopter and antenna during the glaciological survey before performing the real time survey. A tradeoff between scattering parameter (S11) and directivity is considered to propose the optimum distance. The overall antenna structure seems to be a promising candidate for low frequency airborne GPR glacier explorations.

Scientific research needs to rely on valid data to be successful. Magnetic instruments, in particular triaxial magnetometers, can be subject to drifting for various reasons such as temperature variations, loss of alignment, loss of leveling. All these events can have spurious effects on the recorded data. In this article, we show the characterization of one of these cases, the loss of leveling and the changes found on data, as well as the procedure used to correct the effect on the recorded numeric values.

Regular monitoring and tracking of the temperate glacier and polar ice sheets are necessary because of their potential impact on climate change and sea level rise. In this paper, we analyze the airborne 10 MHz bent wire ground penetrating RADAR antenna using different materials. 10 MHz GPR antenna is simulated using different materials such as silver, copper, gold, aluminum, tungsten, zinc, brass, bronze, tin, chromium, indium, lead, titanium, iron, nickel, cobalt, cast iron and graphite. From the simulation results, it is evident that, the conductivity of the material and the radiation efficiency of the antenna are directly proportional to each other. And also, if the relative permeability of the material increases, the radiation efficiency decreases. The S11, VSWR, peak gain and the radiation efficiency of the bent wire GPR antenna are presented for different materials at the solution frequency of 10 MHz.

The first instrument that exploited the radar principle was used to investigate the properties of the ionospheric reflecting layers. Over the decades since then, the techniques have improved and many other types of probing have been developed. The presentation summarises various methodologies, with particular focus on the vertical sounding, and describes the recent improvements, taking into account that in the last years the classic vertical soundings have been joined by new measures of the attenuation undergone by the signal, that are useful to improve the knowledge of the characteristics of the medium.

For the bedrock survey in the temperate glacier regions, low frequency antenna system of the airborne ground penetrating RADAR plays a very important role. A small size antenna, working at 10 MHz, would make its use easier in various radar applications. Reducing the resonant frequency of the wire dipole antenna structure, without increasing the physical size, can be attained by introducing bents in the existing structure. This paper introduces a new bent wire dipole antenna and presents the effects of bent angle of 80 ° , 70 ° , 60 ° , 50 ° , 45 ° and 40 ° of the wire antenna on the antenna parameters such as resonant frequency, S11, VSWR, gain and radiation pattern. A broadband four element equivalent circuit model of a straight dipole is used with some modifications in the R, L, C equations for the new bent wire dipole antenna by utilizing the bent angle. The frequency response of the equivalent circuit model, calculated resonant frequency values using the equations and the simulated results of the bent wire dipole antenna is compared and analyzed. As the antenna placement area inside the anechoic chamber is limited, the size of the 10MHz antenna has been scaled down by a factor of 0.01. This modifies the resonant frequency of the new structure to 1GHz. The scaled down antenna system are simulated, analyzed and tested in a GTEM cell. For bandwidth improvement of the 10 MHz antenna, a lumped element matching circuit has been designed and simulated.

Vertical ionospheric soundings have been performed at almost all ionospheric observatories with little attention to measuring the attenuation of the signal between transmission and reception. When the absorption has been determined, this has been achieved by comparing the received power after the first and second reflections, but this method has some limitations due to the unknown reflection coefficient of the ground and the non-continuous presence of the second reflection. This paper deals with a different method based on precise calibration of the sounding system, allowing determination of absolute signal attenuation after a single reflection. This approach is affected by a systematic error due to imperfect calibration of the antennas, but when the focus of interest is to measure a trend over a specified period, it is very accurate. The article describes how calibration was implemented, the measurement output formats, and finally it presents some results from a meaningful set of measurements in order to demonstrate what this method can accomplish.

Vertical sounding is a widely used technique to obtain ionosphere measurements, such as an estimation of virtual height versus frequency scanning. It is performed by high frequency radar for geophysical applications called "ionospheric sounder" (or "ionosonde"). Radar detection depends mainly on targets characteristics. While several targets behavior and correspondent echo detection algorithms have been studied, a survey to address a suitable algorithm for ionospheric sounder has to be carried out.This paper is focused on automatic echo detection algorithms implemented in particular for an ionospheric sounder, target specific characteristics were studied as well. Adaptive threshold detection algorithms are proposed, compared to the current implemented algorithm, and tested using actual data obtained from the Advanced Ionospheric Sounder (AIS-INGV) at Rome Ionospheric Observatory. Different cases of study have been selected according typical ionospheric and detection conditions. (C) 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.

High Frequency radio waves reflected by the ionosphere can provide a relevant amount of information within the composite received signal. The ionosphere is indeed a frequency dispersive, bi-refractive, absorbing medium, in which multipath propagation occurs due to disturbance on a varied time-spatial scale. On the time-spatial level of Small Scale Disturbances (SSD) the ionosphere dynamics, detectable by Vertical Ionospheric Sounding (VIS), is mainly dependent on wrinkled layers acting as multi-reflectors. The present paper discusses different aspects of the effects of multipath fading suffered by the wave along the propagation path and potentially associated with SSD. To achieve these objectives, a VIS campaign at a fixed frequency of 3.0 MHz was conducted at the ionospheric observatory in Rome (Latitude 41.8 N; Longitude 12.5 E), by collecting a series of measurements of the power variations in received echo signals recorded between two consecutive ionograms whose sounding repetition rate was set to 15 min. The obtained results show that: 1) the fading suffered by the wave follows either a Rayleigh trend or a Nakagami-Rice trend, or a mix of them, the mixed case being the most frequent (about 65 % of the analysed cases); 2) the predominant periodicities characterizing the power variation are less than 25 s; such values are compatible with the small scale ionospheric disturbances; 3) for all the 24 hours of the day the ionospheric reflector is pretty stable and for time intervals of 10-30 s the periods of stability occur with a percentage of occurrence ranging between 55% and 95 %; for time intervals of 190- 210 s the periods of stability occur instead with a percentage of occurrence ranging between 5% and 54 %.

The present paper conducts a scientific review on the complex eikonal, extrapolating the research perspectives on the ionospheric ray-tracing and absorption. As regards the scientific review, the eikonal equation is expressed, and some complex-valued solutions are defined corresponding to complex rays and caustics. Moreover, the geometrical optics is compared to the beam tracing method, introducing the limit of the quasi-isotropic and paraxial complex optics approximations. Finally, the quasi-optical beam tracing is defined as the complex eikonal method applied to ray-tracing, discussing the beam propagation in a cold magnetized plasma. As regards the research perspectives, this paper proposes to address the following scientific problem: in absence of electromagnetic (e.m.) sources, consider a material medium which is time invariant, linear, optically isotropic, generally dispersive in frequency and inhomogeneous in space, with the additional condition that the refractive index is assumed varying even strongly in space. The paper continues the topics discussed by Bianchi et al. [2009], proposing a novelty with respect to the other referenced bibliography: indeed, the Joule's effect is assumed non negligible, so the medium is dissipative, and its electrical conductivity is not identically zero. In mathematical terms, the refractive index belongs to the field of complex numbers. The dissipation plays a significant role, and even the eikonal function belongs to the complex numbers field. Under these conditions, for the first time to the best of our knowledge, suitable generalized complex eikonal and transport equations are derived, never discussed in literature. Moreover, in order to solve the ionospheric ray-tracing and absorption problems, we hint a perspective viewpoint. The complex eikonal equations are derived assuming the medium as optically isotropic. However, in agreement with the quasi isotropic approximation of geometrical optics, these equations can be referred to the Appleton-Hartree's refractive index for an ionospheric magneto-plasma, which becomes only weakly anisotropic in the presence of Earth's magnetic induction field. Finally, a simple formula is deduced for a simplified problem. Consider a flat layering ionospheric medium, so without any horizontal gradient. The paper proposes a new formula, useful to calculate the amplitude absorption due to the ionospheric D-layer, which can be approximately modelled by a linearized complex refractive index, because covering a short range of heights, between h(1) = 50 km and h(2) = 80 km about.

It is well known that the ionosphere affects radio wave propagation especially in the high frequency (HF) range. HF radio waves reflected by the ionosphere can reach considerable distances, often with changes in amplitude, phase, and frequency. The ionosphere is a dispersive in frequency and time, bi-refractive, absorbing medium, in which multipath propagation due to traveling irregularities is very frequent. The traveling irregularities undulate the reflecting ionospheric layer, introducing variations in signal amplitude (fading). In this multipath time variant channel fading is mainly considered, even though it is not the sole effect. Echo signals from a single reflection, as in ionospheric vertical sounding (VIS) techniques, are affected by a certain degree of variability even in quiet ionospheric conditions. In this work the behavior of the ionospheric channel is studied and characterized by observing the power variation of received echoes using the VIS technique. Multipath fading was analyzed quantifying the power variation of the signal echo due to irregularities on a temporal scale from 0.5 to 256 s. An experimental set-up derived from an ionosonde was implemented and the analysis was performed employing a special numerical algorithm operating off-line on the acquired time sequence of the signal. The gain-loss of the irregularity shapes are determined in some special cases. (C) 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

A series of Power Virtual Height measurements (PVH) of radio echoes reflected from the ionosphere were acquired at a given frequency during the period 3–22 January 2008 with the purpose of studying the slow fading variations through time of the ionospheric channel. To obtain PVH data, an ionospheric vertical sounding system was suitably adapted to work at a single fixed frequency. PVH measurements were recorded between two routine ionospheric vertical soundings, providing a data type that enables evaluation of fading fluctuation through time. The time stability of the ionospheric layers is determined by analyzing the level of the received signal power within a chosen threshold. In this paper the fading behaviour and its characteristics are described, considering only temporal periodicity above 0.5s. In a further analysis a relation is demonstrated between the recorded fading and the time stability of the signal within a fixed interval of values.

Radar technology has for a long time used various systems that allow detection under high-resolution conditions, while emitting at the same time low peak power. Among these systems, transmitted pulse encoding by means of biphasic codes has been used for the advanced ionospheric sounder that was developed by the AIS-INGV ionosonde. In the receiving process, suitable decoding of the signal must be accomplished. This can be achieved in both the time and the frequency domains. Focusing on the time domain, different approaches are possible. In this study, two of these approaches have been compared, using data acquired by the AIS-INGV and processed by means of software tools (mainly Mathcad©). The analysis reveals the differences under both noiseless and noisy conditions, although this does not allow the conclusive establishment as to which method is better, as each of them has benefits and drawbacks.

A new digital ionosonde called AIS-INGV (Advanced Ionospheric Sounder) was designed both for research and for routine service of HF radio wave propagation forecast. Nearly the entire system was developed in the Laboratorio di Geofisica Ambientale at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome. It exploits advanced techniques for signal analysis, recent technological devices and PC resources. This paper describes design concepts and performance of the new ionosonde.

The Istituto Nazionale di Geofisica e Vulcanologia has been involved since its foundation in the forecast of the conditions in which a radio link that makes use of propagation by means of ionospheric wave takes place. In the last times it gained interest also the precise forecast of the trajectory covered by a radio wave propagating into the atmosphere, specifically into the ionosphere, which can be considered, at first approximation, as an inhomogeneous medium, defined by a refraction index slowly varying in time.This work describes the theoretical bases to study a trajectory; they substantially make use of the methods of the geometrical optics. Such theoretical bases find applications in numerical methods to calculate the trajectories, as quoted in references [Bianchi, 2009].