Exploiting LF/MF signals of opportunity for lower ionospheric remote sensing

Higginson‐Rollins, M. A.; Cohen, M. B.

doi:10.1002/2017gl074236

Cited by 13 publications

(10 citation statements)

References 43 publications

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“…Terrestrial very low frequency (VLF, 3–30 kHz) and low‐frequency (LF, 30–300 kHz) waves propagate to great distances (>2 Mm) (Higginson‐Rollins & Cohen, ) guided by the Earth ground and the D region of the ionosphere, which form a waveguide commonly known as the Earth‐ionosphere waveguide (EIWG). Therefore, propagating VLF/LF signals carry with them information about the current state of the D region.…”

Section: Introductionmentioning

confidence: 99%

“…The electron densities of the E and F regions of the ionosphere (100-500 km) can be measured more readily by radars or by HF propagation (Alfonsi et al, 2008) to produce reasonably accurate electron density profile estimates, many of which are included in the empirically constructed International Reference Ionosphere Terrestrial very low frequency (VLF, 3-30 kHz) and low-frequency (LF, 30-300 kHz) waves propagate to great distances (>2 Mm) (Higginson-Rollins & Cohen, 2017) guided by the Earth ground and the D region of the ionosphere, which form a waveguide commonly known as the Earth-ionosphere waveguide (EIWG). Therefore, propagating VLF/LF signals carry with them information about the current state of the D region.…”

Section: Introductionmentioning

confidence: 99%

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Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

et al. 2018

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The D region of the ionosphere (60–90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales up to many hundreds of kilometers. Very low frequency (VLF) and low‐frequency (LF) (3–30 kHz and 30–300 kHz) radio waves are guided to global distances by reflections from the ground and the D region. Therefore, information about its current state is encoded in received VLF/LF signals. VLF transmitters have been used in the past for D region studies, with ionospheric disturbances manifesting as perturbations in amplitude and/or phase. The return stroke of lightning is an impulsive VLF radiator, but unlike VLF transmitters, lightning events are distributed broadly in space allowing for much greater spatial coverage of the D region compared to VLF transmitter‐based remote sensing in addition to the broadband spectral advantage over the narrowband transmitters. The challenge is that individual lightning‐generated waveforms, or “sferics,” vary due to the lightning current parameters and uncertainty in the time/location information, in addition to D region ionospheric variability. These factors make it difficult to utilize the VLF/LF emissions from lightning in a straightforward manner. We describe a technique to recover the time domain and amplitude/phase spectra for both Bϕ and Br with high fidelity and consider the utility of our technique with ambient and varied ionospheric conditions. We demonstrate a technique to simulate sferics and infer a parameterized ionosphere with the Wait and Spies parameters (h ′ and β) offering all of the tools needed for a global measurement.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

et al. 2018

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“…The amplitude variations of low‐frequency radio transmissions are also used to monitor the electromagnetic wave propagation in the Earth‐ionosphere cavity (e.g., Inan et al, ; see also Barr et al, , and references therein). Such kind of measurements serve to remote sense the ionized state of the upper atmosphere, that is, the lower D ‐region ionosphere, (e.g., Ohya et al, ; see also Clilverd et al, ; Higginson‐Rollins & Cohen, ; Macotela et al, , and references therein), which responds to space weather, solar variability, and ionospheric modification by lightning discharges (e.g., Shao et al, ; see also Haldoupis et al, ; Kotovsky et al, ; Smith et al, ,, and references therein). The phase of radio transmissions is less often used to determine the ionisation of the lower ionosphere, even though it is an important observation to constrain and enhance the results obtained from amplitude measurements alone (e.g., Thomson et al, ; see also Thomson, ; Thomson et al, , , and references therein).…”

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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“…For instance, Thomson (1993) and Thomson et al (2007) measured VLF transmitter signals at a long distance and Thomson et al (2014) used a mix of short and long distances, and after comparing measurements with a theoretical VLF propagation model, estimated the average ionospheric electron density profile along the path during typical/ambient conditions. Likewise, low frequency (LF, 30-300 kHz) transmitters are used to remotely sense the ionosphere on smaller spatial scales (Higginson-Rollins & Cohen, 2017).…”

Section: Introductionmentioning

confidence: 99%

Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

et al. 2018

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Very low frequency (VLF, 3–30 kHz) transmitter remote sensing has long been used as a simple yet useful diagnostic for the D region ionosphere (60–90 km). All it requires is a VLF radio receiver that records the amplitude and/or phase of a beacon signal as a function of time. During both ambient and disturbed conditions, the received signal can be compared to predictions from a theoretical model to infer ionospheric waveguide properties like electron density. Amplitude and phase have in most cases been analyzed each as individual data streams, often only the amplitude is used. Scattered field formulation combines amplitude and phase effectively, but does not address how to combine two magnetic field components. We present polarization ellipse analysis of VLF transmitter signals using two horizontal components of the magnetic field. The shape of the polarization ellipse is unchanged as the source phase varies, which circumvents a significant problem where VLF transmitters have an unknown source phase. A synchronized two‐channel MSK demodulation algorithm is introduced to mitigate 90° ambiguity in the phase difference between the horizontal magnetic field components. Additionally, the synchronized demodulation improves phase measurements during low‐SNR conditions. Using the polarization ellipse formulation, we take a new look at diurnal VLF transmitter variations, ambient conditions, and ionospheric disturbances from solar flares, lightning‐ionospheric heating, and lightning‐induced electron precipitation, and find differing signatures in the polarization ellipse.

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Exploiting LF/MF signals of opportunity for lower ionospheric remote sensing

Cited by 13 publications

References 43 publications

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

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

Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

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