Comparisons of techniques for measurement of D‐region electron densities

Abstract

This paper reviews the ground‐based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground‐based techniques include VLF, LF, and MF sounding, differential absorption and differential phase using partial reflections, wave interaction, and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high‐resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions, and variances are described.

A Review of Progress in FDTD Maxwell's Equations Modeling of Impulsive Subionospheric Propagation Below 300 kHz

“…However, formulations such as these neglect mode conversion and thus do not apply to strong scatterers. Measurement techniques have included in-situ probing by rockets [81] and remote sensing of radiated spectra generated by random, naturally occurring sources, such as lightning [78]. However, these methods may not provide a practical means to continuously monitor the lower ionosphere and may be difficult or impossible to implement in many regions of the world.…”

Very Low Frequency Remote Sensing Measurements of the Lower Ionosphere at Site of the United Arab Emirates

“…Subionospherically propagating VLF waves are uniquely suited for the investigation of the nighttime D-region, (40-100 km altitudes), so named due to the difficulty of making systematic measurements (Sechrist 1974).…”

“…Measurements of the amplitude and phase of VLF signals propagating in the earth-ionosphere waveguide have long been used effectively for remote sensing of the ionosphere. VLF sounding has been established as a sensitive tool for the measurement of ionospheric conductivity, especially at altitudes below 90 km (e.g., Sechrist 1974), and in recent years has been extensively utilized to study a variety of lower ionospheric disturbances, including those associated with lightning discharges Inan 1993;Burgess and Inan 1993), heating by HF (Bell et al 1993) and VLF waves (Rodriguez et al 1994), the auroral electro-jet (Kikuchi and Evans 1983;Cummer et al 1997), and relativistic electron precipitation enhancements (Demirkol et al 1999).…”

Ionospheric effects of relativistic electron enhancement events

“…Very Low Frequency (VLF) sounding of the lower ionosphere (i.e., the measurement of the amplitude and phase of subionospherically propagating VLF signals) is a sensitive tool for the detection of ionospheric conductivity changes due to changes in electron density and/or temperature, especially at altitudes below 90 km [Sechrist, 1974]. Some of the early work on relativistic electron precipitation events has indeed relied on subionospheric VLF measurements [Thorne and Larsen, 1976].…”