Effective Electron Density Distributions Describing VLF/LF Propagation Data

Morfitt, David G.

doi:10.21236/ada047508

Cited by 18 publications

(17 citation statements)

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“…Theoretically calculated signal strength as a function of distance and frequency from a VLF transmitter are shown for day and night in Fig.16 [28]. These calculations are not necessarily accurate for specific paths but show the general variation of direct modal interference expected for propagation over a mid-latitude path between Hawaii and California.…”

Section: Direct Modal Interferencementioning

confidence: 99%

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VLF Waveguide Propagation: The Basics

Lynn¹

2010

AIP Conference Proceedings

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In recent times, research has moved towards using VLF radio transmissions propagating in the earth-ionosphere waveguide as a detector of a variety of transient geophysical phenomena. A correct interpretation of such results depends critically on understanding the propagation characteristics of the path being monitored. The observed effects will vary depending on time of day, path length, path orientation, magnetic latitude and VLF frequency. This paper provides a brief tutorial of the relevant propagation dependencies for medium to long VLF paths best understood in terms of waveguide mode theory together with results either not previously published, not published in the open scientific literature or whose significance has been little recognised.

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Section: Direct Modal Interferencementioning

confidence: 99%

“…The attenuation increases with mode order so that the summed signal simplifies with distance FIGURE 16. Computed VLF signal strength for day and night over a fixed path showing the variation of mode interference with frequency and distance for day and night conditions [28].…”

Section: Direct Modal Interferencementioning

confidence: 99%

VLF Waveguide Propagation: The Basics

Lynn¹

2010

AIP Conference Proceedings

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“…These programs take the input path parameters, calculate appropriate full wave reflection coefficients for the waveguide boundaries, and search for those modal angles which give a phase change of 2p across the guide, taking into account the curvature of the Earth [e.g., Morfitt and Shellman, 1976;Ferguson and Snyder, 1990]. Further discussions of the NOSC waveguide programs and comparisons with experimental data can be found in the work of Bickel et al [1970], Morfitt [1977], Ferguson [1980], Morfitt et al [1981], Thomson [1993], Ferguson [1995], Cummer et al [1998], McRae and Thomson [2000Thomson [ , 2004, Thomson and Clilverd [2001], Thomson et al [2005Thomson et al [ , 2007, Thomson and McRae [2009], Thomson [2010], and Cheng et al [2006].…”

Section: Introductionmentioning

confidence: 99%

“…This also applies for LWPC version 2 [Ferguson, 1998]. Previously [International Radio Consultative Committee, 1990;Morfitt, 1977], NOSC recommended H′ = 70 km with b = 0.5 km −1 for summer midlatitudes (and by implication low latitudes) and H′ = 72 km with b = 0.3 km −1 for summer high latitudes. Their midlatitudes were separated from their high latitudes by a transition region with magnetic dip angles in the range 70-75°corresponding to a geomagnetic latitude range of 54-62°.…”

Section: Introductionmentioning

confidence: 99%

Daytime midlatitudeDregion parameters at solar minimum from short-path VLF phase and amplitude

2011

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[1] Observed phases and amplitudes of VLF radio signals propagating on a short (∼360 km) path are used to find improved parameters for the lowest edge of the (D region of the) Earth's ionosphere at a geomagnetic latitude of ∼53.5°in midsummer near solar minimum. The phases, relative to GPS 1 s pulses, and the amplitudes were measured both near (∼110 km from) the transmitter, where the direct ground wave is very dominant, and at distances of ∼360 km near where the ionospherically reflected waves form a (modal) minimum with the (direct) ground wave. The signals came from the 24.0 kHz transmitter, NAA, on the coast of Maine near the U.S.-Canada border, propagating ∼360 km E-NE, mainly over the sea, to Saint John and Prince Edward Island. The bottom edge of the midday, midsummer, ionosphere at ∼53.5°geomagnetic latitude was thus found to be well modeled by H′ = 71.8 ± 0.6 km and b = 0.335 ± 0.025 km −1 where H′ and b are Wait's traditional height and sharpness parameters used by the U.S. Navy in their Earth-ionosphere VLF radio waveguide programs. The variation of b with latitude is also estimated with the aid of interpolation using measured galactic cosmic ray fluxes.

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“…Lehtinen and Inan (2008) present a model using the full-wave finite element method; Chevalier and Inan (2006) and Marshall and Inan (2010) use finite difference frequency domain methods; and Thiel and Mittra (1997), Thevenot et al (1999), and Hu and Cummer (2006) each use finite difference time domain-based models. It is a popular choice because it has been extensively validated (Ferguson, 1980;Morfitt, 1977) and runs very quickly compared to finite difference frequency domain and finite difference time domain models, and it is the propagation model we use in this work. One of the most common VLF mode-finding programs is called Long-Wavelength Propagation Capability (LWPC) (Ferguson, 1998).…”

Section: Vlf Propagation Modelingmentioning

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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Effective Electron Density Distributions Describing VLF/LF Propagation Data

Cited by 18 publications

References 0 publications

VLF Waveguide Propagation: The Basics

VLF Waveguide Propagation: The Basics

Daytime midlatitudeDregion parameters at solar minimum from short-path VLF phase and amplitude

VLF Remote Sensing of the D Region Ionosphere Using Neural Networks

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