Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

Gross, N. C.; Cohen, M. B.; Said, R.; Gołkowski, M.

doi:10.1002/2017ja024907

Cited by 35 publications

(48 citation statements)

References 56 publications

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“…It is also significant that because VLF sferics are not perfectly linearly polarized, the low‐SNR channel still has a detectable magnetic field which can be recovered with this technique, not yet utilized in former sferic studies. Recent results from Gross et al () utilize phase and amplitude of both Bϕ and B r of narrowband VLF signals to develop a polarization ellipse method to monitor the D Region and diagnose ionospheric perturbations, with advantages over previous narrowband studies. Similarly, amplitude and phase of both Bϕ and B r of broadband sferics recovered in this study may reveal or clarify information on the D Region and related phenomena.…”

Section: Methodsmentioning

confidence: 99%

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: Methodsmentioning

confidence: 99%

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

et al. 2018

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“…We use the synchronized demodulation technique developed by Gross et al (2018) to extract the complex-valued radial B r and azimuthal B magnetic flux densities, wherer points in the direction of propagation along the GCP and̂is in the horizontal plane and perpendicular tor. Amplitude and phase of the magnetic flux density at the center frequency are found by demodulating the transmitted signal.…”

Section: Journal Of Geophysical Research: Space Physicsmentioning

confidence: 99%

VLF Remote Sensing of the D Region Ionosphere Using Neural Networks

Gross

Cohen

2020

JGR Space Physics

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Narrowband very low frequency (VLF) remote sensing has proven to be a useful tool for characterizing the ionosphere's D region (60-to 90-km altitude) electron density. This work expands upon single transmitter-receiver pair electron density profile inference methods to create a more generalized narrowband VLF remote sensing method that concurrently resolves a two-parameter electron density profile for an arbitrary number of transmitter-receiver pairs. A target function is constructed to take in a single time step of narrowband amplitude and phase observations from an arbitrary number of transmitter and receiver combinations and return the inferred average waveguide parameters along all paths. The target function is approximated using an artificial neural network (ANN). Synthetic training data are generated using the U.S. Navy's Long-Wavelength Propagation Capability program, which is then used to train the ANN. Performance of the ANN with real-world data is measured in two ways. First, ANN inferred average waveguide parameters are compared to a variety of previously published narrowband VLF remote sensing experiments. Second, ANN inferred average waveguide parameters are used in Long-Wavelength Propagation Capability to predict narrowband VLF amplitude and carrier phase at a receiver that was withheld when performing the average waveguide parameter inference. Results show the approximated target function performs well in capturing temporal and spatial characteristics of the D region.

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“…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). The main reason why phase measurements are less common is that the associated signal processing has a larger degree of complexity (e.g., Gross et al, ; Koh et al, , and references therein). More recently, phase measurements of lightning discharges have become of increasing interest, partly to determine the impact of lightning on the lower ionosphere (McCormick et al, ) or for their use in lightning detection networks (Liu et al, ; see also Dowden et al, ; Liu 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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Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

Cited by 35 publications

References 56 publications

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

VLF Remote Sensing of the D Region Ionosphere Using Neural Networks

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

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