A Consideration on Appropriate Parameters for Identifying Electron Density Profile in the Lower Ionosphere by using VLF Wave Propagation in the Earth-Ionosphere Waveguide
01 Aug 2017-Electronics and Communications in Japan (Wiley)-Vol. 100, Iss: 8, pp 16-23
About: This article is published in Electronics and Communications in Japan.The article was published on 2017-08-01. It has received 1 citations till now. The article focuses on the topics: Earth–ionosphere waveguide & Ionosphere.
01 Dec 2018
TL;DR: The characteristics of VLF wave propagation in earth-ionosphere waveguide are analyzed and the influence of ground electrical characteristics, ionospheric electrical characteristics and wave characteristic parameters on the communication of underwater platforms is pointed out.
Abstract: VLF communication is one of the most effective means to command underwater platform at present. However, the reliability of VLF communication will be degraded due to various factors in the process of VLF signal propagation. In this paper, the characteristics of VLF wave propagation in earth-ionosphere waveguide are analyzed. The influence of ground electrical characteristics, ionospheric electrical characteristics and wave characteristic parameters on the communication of underwater platforms is pointed out. By studying these laws and making use of the good predictability of the VLF band, the attenuation and disturbance in the propagation process can be predicted. So we can achieve the best communication effect and improve the reliability of the underwater platform VLF communication.
TL;DR: The International Reference Ionosphere (IRI) is the de facto international standard for the climatological specification of ionospheric parameters and as such it is currently undergoing registration as Technical Specification (TS) of the International Standardization Organization (ISO) as discussed by the authors.
TL;DR: In this article, a series of mode theory and FDTD simulations of propagation from lightning radiation in the Earth-ionosphere waveguide were performed to investigate the accuracy of these approximations.
Abstract: The ionosphere plays a role in radio propagation that varies strongly with frequency. At extremely low frequency (ELF: 3-3000 Hz) and very low frequency (VLF: 3-30 kHz), the ground and the ionosphere are good electrical conductors and form a spherical Earth-ionosphere waveguide. Many giants of the electromagnetics (EMs) community studied ELF-VLF propagation in the Earth-ionosphere waveguide, a topic which was critically important for long-range communication and navigation systems. James R. Wait was undoubtedly the most prolific publisher in this field, starting in the 1950s and continuing well into the 1990s. Although it is an old problem, there are new scientific and practical applications that rely on accurate modeling of ELF-VLF propagation, including ionospheric remote sensing, lightning remote sensing, global climate monitoring, and even earthquake precursor detection. The theory of ELF-VLP propagation in the Earth-ionosphere waveguide is mature, but there remain many ways of actually performing propagation calculations. Most techniques are based on waveguide mode theory with either numerical or approximate analytical formulations, but direct finite-difference time-domain (FDTD) modeling is now also feasible. Furthermore, in either mode theory or FDTD, the ionospheric upper boundary can be treated with varying degrees of approximation. While these approximations are understood in a qualitative sense, it is difficult to assess in advance their applicability to a given propagation problem. With a series of mode theory and FDTD simulations of propagation from lightning radiation in the Earth-ionosphere waveguide, we investigate the accuracy of these approximations. We also show that fields from post-discharge ionospheric currents and from evanescent modes become important at lower ELF (/spl lsim/500 Hz) over short distances (/spl lsim/500 km). These fields are not easily modeled with mode theory, but are inherent in the FDTD formulation of the problem. In this way, the FDTD solution bridges the gap between analytical solutions for fields close to and far from the source.
TL;DR: In this paper, the authors developed a model of sferic propagation which is based on an existing frequency domain subionospheric VLF propagation code and derived the electron density profile that most closely matched an observed sferric spectrum.
Abstract: Lightning discharges radiate the bulk of their electromagnetic energy in the very low frequency (VLF, 3–30 kHz) and extremely low frequency (ELF, 3–3000 Hz) bands. This energy, contained in impulse-like signals called radio atmospherics or sferics, is guided for long distances by multiple reflections from the ground and lower ionosphere. This suggests that observed sferic waveforms radiated from lightning and received at long distances (>1000 km) from the source stroke contain information about the state of the ionosphere along the propagation path. The focus of this work is on the extraction of nighttime D region electron densities (in the altitude range of ∼70–95 km) from observed VLF sferics. In order to accurately interpret observed sferic characteristics, we develop a model of sferic propagation which is based on an existing frequency domain subionospheric VLF propagation code. The model shows that the spectral characteristics of VLF sferics depend primarily on the propagation path averaged ionospheric D region electron density profile, covering the range of electron densities from ∼100 to 103 cm−3. To infer the D region density from observed VLF sferics, we find the electron density profile that produces a modeled sferic spectrum that most closely matches an observed sferic spectrum. In most nighttime cases the quality of the agreement and the uncertainties involved allow the height of an exponentially varying electron density profile to be inferred with a precision of ∼0.2 km.
TL;DR: A review of the development of ELF and VLF measurements, both from a historical point of view and from the view of their relationship to optical and other observations of ionospheric effects of lightning discharges is provided in this paper.
Abstract:  Extremely low frequency (ELF) and very low frequency (VLF) observations have formed the cornerstone of measurement and interpretation of effects of lightning discharges on the overlying upper atmospheric regions, as well as near‐Earth space. ELF (0.3–3 kHz) and VLF (3–30 kHz) wave energy released by lightning discharges is often the agent of modification of the lower ionospheric medium that results in the conductivity changes and the excitation of optical emissions that constitute transient luminous events (TLEs). In addition, the resultant ionospheric changes are best (and often uniquely) observable as perturbations of subionospherically propagating VLF signals. In fact, some of the earliest evidence for direct disturbances of the lower ionosphere in association with lightning discharges was obtained in the course of the study of such VLF perturbations. Measurements of the detailed ELF and VLF waveforms of parent lightning discharges that produce TLEs and terrestrial gamma ray flashes (TGFs) have also been very fruitful, often revealing properties of such discharges that maximize ionospheric effects, such as generation of intense electromagnetic pulses (EMPs) or removal of large quantities of charge. In this paper, we provide a review of the development of ELF and VLF measurements, both from a historical point of view and from the point of view of their relationship to optical and other observations of ionospheric effects of lightning discharges.
TL;DR: In this paper, the authors used the differential-times-of-arrival (DTOR) of lightning sferics recorded by three or more stations to determine the source height of the source.
Abstract:  The Los Alamos Sferic Array (LASA) recorded VLF/LF electric-field-change signals from over ten million lightning discharges during the period from 1998 to 2001. Using the differential-times-of-arrival of lightning sferics recorded by three or more stations, the latitudes and longitudes of the source discharges were determined. Under conditions of favorable geometry and ionospheric propagation, sensors obtained ionospherically reflected skywave signals from the lightning discharges in addition to the standard groundwave sferics. In approximately 1% of all waveforms, automated processing identified two 1-hop skywave reflection paths with delays indicative of an intracloud (height greater than 5 km) lightning source origin. For these events it was possible to determine both the height of the source above ground and the virtual reflection height of the ionosphere. Ionosphere heights agreed well with published values of 60 to 95 km with an expected diurnal variation. Source height determinations for 100,000+ intracloud lightning events ranged from 7 to 20 km AGL with negative-polarity events occurring above ∼15 km and positive-polarity events occurring below ∼15 km. The negative-polarity events are at a suprisingly high altitude and may be associated with discharges between the upper charge layer of a storm and a screening layer of charge above the storm. Approximately 100 of the intracloud events with LASA height determinations were also recorded by VHF receivers on the FORTE satellite. Independent FORTE source height estimates based on delays between direct and ground-reflected radio emissions showed excellent correlation with the VLF/LF estimates, but with a +1 km bias for the VLF/LF height determinations.