Array analysis of electromagnetic radiation from radio transmitters for submarine communication

Füllekrug, Martin; Mezentsev, Andrew; Watson, Robert J.; Gaffet, Stéphane; Astin, Ivan; Evans, A.N.

doi:10.1002/2014gl062126

Cited by 13 publications

(27 citation statements)

References 27 publications

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“…Each receiver is a wideband vertical electric field sensor that samples every 1 μs, with an amplitude resolution of ∼35 μV/m and timing accuracy of ∼20 ns (Füllekrug, ). The accuracy of the array measurements has been shown to be close to instrumental limits (Füllekrug et al, , section 6). The time of the recording analyzed in this study is a 6‐s period from 15:00:03 to 15:00:09 UTC on 13 May 2011.…”

Section: Experimental Datamentioning

confidence: 70%

Lower Ionosphere Effects on Narrowband Very Low Frequency Transmission Propagation: Fast Variabilities and Frequency Dependence

2018

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The man‐made narrowband very low frequency transmission from Rhauderfehn, Germany, is studied using high accuracy, microsecond time resolution measurements in Bath, UK. The high time resolution enables a novel comparison of the measurements with a detailed simulation of the transmitted signal. It is found that the wave propagation frequency response exhibits nonlinear amplitude and phase changes with frequency over the narrow transmission bandwidth during the time of the measurements (13 May 2011 15:00:03–15:00:09 UTC). The high time resolution also enables measurements of fast variabilities in the wave propagation <5 ms. The fast propagation variabilities are likely to originate from integrated ionospheric variability over the propagation path or fast ionospheric processes. The wave propagation frequency response measurement has potential benefits in the study of the lower ionosphere, in particular during highly variable perturbations such as those caused by lightning.

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Section: Experimental Datamentioning

confidence: 70%

Lower Ionosphere Effects on Narrowband Very Low Frequency Transmission Propagation: Fast Variabilities and Frequency Dependence

2018

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“…The array analysis described in section 2 is specifically designed to infer robust estimates for the wave number vector, electromagnetic source field, and the spatial and temporal quality of low‐frequency radio waves with small electric field strengths observed with an array. Here we make use of recordings with an array of N = 10 radio receivers distributed over an area ∼1 km × 1 km on Charmy Down airfield near Bath in the UK (Füllekrug et al, ; Mezentsev & Füllekrug, ). Electric field strengths are measured with a sampling frequency of 1 MHz, an amplitude resolution of ∼25μV/m and a timing uncertainty ∼20 ns (Füllekrug, ).…”

Section: Continuum Radiationmentioning

confidence: 99%

“…Yet the electromagnetic source field incorporates all the information about the physical processes that cause the observed radio waves. The electromagnetic source field can be displayed in a constellation diagram, which is a bivariate distribution function for the normalized real and imaginary part of the electromagnetic source field (Füllekrug et al, , Figure 2, right). Here we make use of the pulsed radio transmissions from the UK radio clock at 60 (±1) kHz, LORAN transmitters for marine navigation at 100 (±10) kHz (Mezentsev & Füllekrug, ; Füllekrug et al, , and references therein), and lightning discharges at 10 (±5) kHz toward a more detailed assessment of continuum radiation.…”

Section: Continuum Radiationmentioning

confidence: 99%

Detection of Low‐Frequency Continuum Radiation

et al. 2018

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The electromagnetic spectrum at low frequencies from ∼3 to 300 kHz is dominated by impulses from lightning discharges and anthropogenic radio transmissions used for communication. Electromagnetic waves generated in near‐Earth space exhibit generally smaller amplitudes that are attenuated when travelling through the ionosphere before they can be observed at high and midlatitudes. Electromagnetic waves with yet smaller amplitudes contribute to the overall electromagnetic energy trapped within the Earth‐ionosphere cavity. At this point, the electromagnetic waves from all possible sources blend into an unstructured continuum radiation near the instrumental noise floor, which is often considered to be a fundamental limit to scientific discovery. As a result, the sources of continuum radiation have been little studied and are essentially unknown. Here we show how low‐frequency continuum radiation is detected and discriminated against known radio sources and instrumental noise by use of rigorous criteria inferred from novel precision measurements with an array of radio receivers. In particular, it is found that coherent continuum radiation from intermittent radio transmitters exhibits electric field strengths 0.5–0.7 μV/m, which are almost 2 orders of magnitude smaller when compared to the noise floor of the radio receivers ∼25 μV/m. Another part of the continuum radiation is found at local zenith above the array when it is caused by random instrumental noise. The results exemplify the possibility to extract sources from continuum radiation to study their origin and physical properties, which can contribute to an improved understanding of the impact of space weather and solar variability on the Earth's upper atmosphere.

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“…Similarly, the exemplary phase stability of chorus wave packets in near Earth space was determined on board of Van Allen Probe spacecraft by explicit use of the instantaneous frequency (Santolik et al, ). More recently, the phase stability has been used to map the source locations of electromagnetic signals in the sky (Füllekrug et al, ; see also Füllekrug, Mezentsev, et al, ; Füllekrug, Smith, et al, ; Füllekrug et al, ). This phase stability is an important prerequisite to successfully map well‐focused source locations in the sky, in particular for the coherent signals of continuum radiation that are found up to 2 orders of magnitude below the noise floor of the radio receivers used (Füllekrug et al, ).…”

Section: Introductionmentioning

confidence: 99%

First Map of Coherent Low‐Frequency Continuum Radiation in the Sky

et al. 2019

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Lightning discharges and radio transmitters emit low‐frequency (∼3–300 kHz) electromagnetic waves with large electric field strengths and stable phases. This phase stability makes it possible to map the source locations of lightning and transmitters in the sky. Electromagnetic waves with smaller electric field strengths generally exhibit a reduced phase stability, caused by numerous simultaneous physical processes that blend into an underlying continuum radiation trapped inside the Earth‐ionosphere cavity. It is therefore currently not known whether the source locations of continuum radiation can be determined. Here we show the first map of coherent continuum radiation in the sky above an array of high‐precision radio receivers. The source locations of the coherent continuum radiation are found at elevation angles ∼30∘−60∘ above the horizon. The identified source locations are attributed to intermittent radio transmitters that emit electromagnetic waves with electric field strengths ∼2 orders of magnitude below the instrumental noise floor. The results demonstrate that it is possible to simultaneously map the signals from coherent continuum radiation, lightning discharges, and radio transmitters in the sky. This work thereby lays the foundation toward the discovery of many more coherent source locations of low‐frequency electromagnetic waves in the sky. It is expected that the identified source locations vary with time as a result of the impact of solar variability on the D‐region ionosphere. Future studies have therefore the potential to contribute to a novel remote sensing and an improved understanding of the D‐region ionosphere, influenced by the near‐Earth space environment.

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Array analysis of electromagnetic radiation from radio transmitters for submarine communication

Cited by 13 publications

References 27 publications

Lower Ionosphere Effects on Narrowband Very Low Frequency Transmission Propagation: Fast Variabilities and Frequency Dependence

Lower Ionosphere Effects on Narrowband Very Low Frequency Transmission Propagation: Fast Variabilities and Frequency Dependence

Detection of Low‐Frequency Continuum Radiation

First Map of Coherent Low‐Frequency Continuum Radiation in the Sky

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