Navigation with Low‐Frequency Radio Signals

2020 ◽  
pp. 1281-1333
Author(s):  
Wouter Pelgrum ◽  
Charles Schue
Keyword(s):  
Low Frequency ◽  
Radio Signals

On the characterization of VLF radio signal propagation in atmosphere in quite solar conditions

2020 ◽  
Author(s):  
Giovanni Nico ◽  
Aleksandra Nina ◽  
Anita Ermini ◽  
Pierfrancesco Biagi
Keyword(s):  
Radio Signal ◽  
Technological Development ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Signal Propagation ◽  
Temporal Variations ◽  
Seasonal Effects ◽  
Propagation Mode ◽  
Theory Approach ◽  
Radio Signals

<p>In this work we use Very Low Frequency (VLF) radio signals, having a frequency in the bands 20-80 kHz, to study the VLF signal propagation in the atmosphere quite undisturbed conditions by selecting the signals recorded during night. As a good approximation, we can model the propagation of VLF radio signals as characterized by a ground-wave and a sky-wave propagation mode. The first one generates a radio signal that propagates in the channel ground-troposphere, while the second one generates a signal which propagates using the lower ionosphere as a reflector. The VLF receivers of the INFREP (European Network of Electromagnetic Radiation) network are used. These receivers have been installed since 2009 mainly in southern and central Europe and currently the INFREP network consists of 9 receivers. A 1-minute sampling interval is used to record the amplitude of VLF signals. Long time-series of VLF signals propagating during night are extracted from recorded signals to study possible seasonal effects due to temporal variations in the physical properties of troposphere. A graph theory approach is used to investigate the spatial correlation of the aforementioned effects at different receivers. A multivariate analysis is also applied to identify common temporal changes observed at VLF receivers.</p><p>This work was supported by the Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR), Italy, under the project OT4CLIMA. This research is supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, under the projects 176002 and III44002.</p>

Optimisation of a device for pick-up of low-frequency radio signals and transmission over polymer optical fibres

2012 ◽  
Vol 68 (1-2) ◽  
pp. 81-93 ◽  
Author(s):  
Ricardo M. Ribeiro ◽  
Andrés P. L. Barbero ◽  
Odair S. Xavier ◽  
Jorge A. M. Souza ◽  
Marbey M. Mosso
Keyword(s):  
Low Frequency ◽  
Optical Fibres ◽  
Radio Signals

scholarly journals Characterization of gravity waves in the lower ionosphere using very low frequency observations at Comandante Ferraz Brazilian Antarctic Station

2020 ◽  
Vol 38 (2) ◽  
pp. 385-394
Author(s):  
Emilia Correia ◽  
Luis Tiago Medeiros Raunheitte ◽  
José Valentin Bageston ◽  
Dino Enrico D'Amico
Keyword(s):  
Low Frequency ◽  
Lower Ionosphere ◽  
Drake Passage ◽  
Wave Period ◽  
Very Low Frequency ◽  
Reflection Height ◽  
D Region ◽  
Radio Signals ◽  
Sky Conditions ◽  
The Waves

Abstract. The goal of this work is to investigate the gravity wave (GW) characteristics in the low ionosphere using very low frequency (VLF) radio signals. The spatial modulations produced by the GWs affect the conditions of the electron density at reflection height of the VLF signals, which produce fluctuations of the electrical conductivity in the D region that can be detected as variations in the amplitude and phase of VLF narrowband signals. The analysis considered the VLF signal transmitted from the US Cutler, Maine (NAA) station that was received at Comandante Ferraz Brazilian Antarctic Station (EACF, 62.1∘ S, 58.4∘ W), with its great circle path crossing the Drake Passage longitudinally. The wave periods of the GWs detected in the low ionosphere are obtained using the wavelet analysis applied to the VLF amplitude. Here the VLF technique was used as a new aspect for monitoring GW activity. It was validated comparing the wave period and duration properties of one GW event observed simultaneously with a co-located airglow all-sky imager both operating at EACF. The statistical analysis of the seasonal variation of the wave periods detected using VLF technique for 2007 showed that the GW events occurred all observed days, with the waves with a period between 5 and 10 min dominating during night hours from May to September, while during daytime hours the waves with a period between 0 and 5 min are predominant the whole year and dominate all days from November to April. These results show that VLF technique is a powerful tool to obtain the wave period and duration of GW events in the low ionosphere, with the advantage of being independent of sky conditions, and it can be used during the whole day and year-round.

scholarly journals Relativistic electron beams above thunderclouds

2011 ◽  
Vol 11 (5) ◽  
pp. 15551-15572
Author(s):  
M. Füllekrug ◽  
R. Roussel-Dupré ◽  
E. M. D. Symbalisty ◽  
J. J. Colman ◽  
O. Chanrion ◽  
...  
Keyword(s):  
Electron Beam ◽  
Relativistic Electron ◽  
Electron Beams ◽  
Low Frequency ◽  
Electric Circuit ◽  
Total Charge ◽  
Relativistic Electron Beams ◽  
Radio Signals ◽  
Lightning Discharges ◽  
Cloud To Ground Lightning

Abstract. Non-luminous relativistic electron beams above thunderclouds are detected by radio remote sensing with low frequency radio signals from 40–400 kHz. The electron beams occur 2–9 ms after positive cloud-to-ground lightning discharges at heights between 22–72 km above thunderclouds. The positive lightning discharges also cause sprites which occur either above or before the electron beam. One electron beam was detected without any luminous sprite occurrence which suggests that electron beams may also occur independently. Numerical simulations show that the beamed electrons partially discharge the lightning electric field above thunderclouds and thereby gain a mean energy of 7 MeV to transport a total charge of 10 mC upwards. The impulsive current associated with relativistic electron beams above thunderclouds is directed downwards and needs to be considered as a novel element of the global atmospheric electric circuit.

scholarly journals ALGORITHM FOR DETERMINING PHASE SHIFT OF HARMONIC SIGNALS USING STOCHASTIC DISCRETIZATION

2019 ◽  
pp. 90-96
Author(s):  
Irina Nikolaevna Zaitseva
Keyword(s):  
Mathematical Modeling ◽  
Phase Shift ◽  
Low Frequency ◽  
Practical Application ◽  
Distribution Law ◽  
Time Intervals ◽  
Harmonic Signals ◽  
Radio Signals ◽  
Basic Parameters ◽  
Signal Period

The article focuses on the problem of estimating basic parameters of harmonic signals. An algorithm for determining the phase shift of such signals by the probabilistic-statistical method is proposed. An important advantage of the algorithm is the fact that the circulation time is aliquant to the signal period or shorter. It is important when measuring parameters of infra-low-frequency radio signals. Mathematical modeling of the algorithm was carried out to study errors and assess the possibility of practical application of the algorithm for processing infra-low-frequency radio signals at stochastic discretization. The results of a numerical experiment show that the error of determining the phase shift of harmonic signals using the developed algorithm on the basis of integral samples with stochastic discretization of time intervals according to the uniform distribution law is 1/100 of a percent, and little depends on the accuracy of signal discretization by level. The error obtained corresponds to the accuracy of discretization when translating the 12-bit ADCs into analog-digital converters. The proposed algorithm can be applied for processing infra-low-frequency radio signals in acoustics and communication, as well as in geophysical and biomedical research.

scholarly journals How can the Fourier Transform be Used in Radio Astronomy to Perform Spectral Analysis of Pulsars

2021 ◽  
Vol 10 (2) ◽  
Author(s):  
Pranesh Kumar ◽  
Arthur Western
Keyword(s):  
Spectral Analysis ◽  
Fourier Transform ◽  
Discrete Fourier Transform ◽  
Low Frequency ◽  
Radio Frequency Interference ◽  
Radio Waves ◽  
Folding Algorithm ◽  
Radio Signals ◽  
Multiple Characteristics ◽  
The Fourier Transform

The analysis of pulsars is a complicated procedure due to the influence of background radio waves. Special radio telescopes designed to detect pulsar signals have to employ many techniques to reconstruct interstellar signals and determine if they originated from a pulsating radio source. The Discrete Fourier Transform on its own has allowed astronomers to perform basic spectral analysis of potential pulsar signals. However, Radio Frequency Interference (RFI) makes the process of detecting and analyzing pulsars extremely difficult. This has forced astronomers to be creative in identifying and determining the specific characteristics of these unique rotating neutron stars. Astrophysicists have utilized algorithms such as the Fast Fourier Transform (FFT) to predict the spin period and harmonic frequencies of pulsars. However, FFT-based searches cannot be utilized alone because low-frequency pulsar signals go undetected in the presence of background radio noise. Astrophysicists must stack up pulses using the Fast Folding Algorithm (FFA) and utilize the coherent dedispersion technique to improve FFT sensitivity. The following research paper will discuss how the Discrete Fourier Transform is a useful technique for detecting radio signals and determining the pulsar frequency. It will also discuss how dedispersion and the pulsar frequency are critical for predicting multiple characteristics of pulsars and correcting the influence of the Interstellar Medium (ISM).

scholarly journals Suppression of very low frequency radio noise in transient electromagnetic data with semi-tapered gates

2021 ◽  
Vol 10 (1) ◽  
pp. 81-90
Author(s):  
Jakob Juul Larsen ◽  
Stine Søgaard Pedersen ◽  
Nikolaj Foged ◽  
Esben Auken
Keyword(s):  
Standard Error ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Side Lobe ◽  
Late Time ◽  
Very Low Frequency ◽  
Transient Electromagnetic ◽  
Noise Rejection ◽  
Radio Signals ◽  
Subsurface Resistivity

Abstract. The transient electromagnetic method (TEM) is widely used for mapping subsurface resistivity structures, but data are inevitably contaminated by noise from various sources. It is common practice to gate signals from TEM systems to reduce the amount of data and improve the signal-to-noise ratio (SNR). Gating acts as a filter, and optimum gating will pass the TEM signal un-attenuated while suppressing noise. In systems based on analog boxcar integrators, the gating corresponds to filtering with a square window. The frequency response of this window shape has large side lobes, which are often insufficient in attenuating noise, e.g., from radio signals in the very low frequency (VLF) 3–30 kHz band. Tapered gates have better side lobe suppression and attenuate noise better, but tapering with analog boxcar integrators is difficult. We propose using many short boxcar gates, denoted sub-gates, and combine the sub-gates into semi-tapered gates to improve noise rejection at late gates where low signal normally leads to poor SNR. The semi-tapering approach is analyzed and tested experimentally on data from a roving TEM system. We quantify the effect of semi-tapered gates by computing an improvement factor as the ratio between the standard error of data measured with boxcar gates and the standard error of data measured with semi-tapered gates. Data from a test survey in Gedved, Denmark, with 1825 measurements gave mean improvement factors between 1.04 and 2.22 for the 10 late-time gates centered between 78.7 and 978.1 µs. After inversion of the data, we find that semi-tapering increases the depth of investigation by about 20 % for this specific survey. We conclude that the semi-tapered approach is a viable path towards increasing SNR in TEM systems based on analog boxcar integrators.

Observation and Analysis of Solar Flares that Cause Large-area Short-wave Communication Interruption

2021 ◽  
Author(s):  
Zhou Kangpo ◽  
Niu youtian ◽  
Liu weina ◽  
Wang zhaodi ◽  
Guo songhao ◽  
...  
Keyword(s):  
Solar Flares ◽  
Ionospheric Disturbance ◽  
Low Frequency ◽  
High Energy ◽  
Short Wave ◽  
Absorption Capacity ◽  
X Rays ◽  
Large Area ◽  
Radio Signals ◽  
Shortwave Communication

Abstract When a solar flare erupts, the sun emits a flood of X-rays and high-energy particles that reach Earth at the speed of light, causing a sudden ionospheric disturbance event (SID event). The D layer of the ionosphere absorbs high-frequency radio signals. With the increase of flare intensity, the D layer's absorption capacity becomes stronger, which leads to the decline of shortwave communication quality and even the interruption of shortwave communication. In this paper, solar flares, which caused large area short-wave communication interruption in recent years, are observed and analyzed by very low frequency (VLF) method, and the influence of solar flares on short-wave communication is summarized. Finally, several methods to deal with the short-wave communication interruption caused by solar flares are proposed.

scholarly journals ADVANCED DETECTION METHODS OF RADIO SIGNALS FROM COSMIC RAYS FOR KASCADE GRANDE AND AUGER

2006 ◽  
Vol 21 (supp01) ◽  
pp. 242-246 ◽  
Author(s):  
H. GEMMEKE ◽  
W. D. APEL ◽  
F. A. BADEA ◽  
L. BÄHREN ◽  
K. BEKK ◽  
...  
Keyword(s):  
Cosmic Rays ◽  
Low Frequency ◽  
Extensive Air Showers ◽  
Detection Methods ◽  
Next Generation ◽  
Air Showers ◽  
Array Technology ◽  
Radio Signals ◽  
Radio Measurements ◽  
Positive Results

The LOPES experiment (LOfar Prototype Station) has been built at the KASCADE-Grande experiment in order to test the LOFAR (LOw Frequency ARray) technology and demonstrate its capability for radio measurements in Extensive Air Showers (EAS). After the first positive results in the framework of the KASCADE-Grande experiment we developed the next generation of antennas, electronics, and trigger. The main new features are easy calibration of antennas with precise detection of polarization, and good capability of self-triggering. The results from this new design are under test in Karlsruhe. Furthermore the background situation was measured and analyzed.

Sign in / Sign up

Export Citation Format

Share Document