Dependence of very-low-frequency electric field antenna impedance on magnetospheric plasma density

Abstract

Data from a VLF electric field antenna on board the spacecraft OV3‐3 show that the antenna response depends upon the local plasma density. Antenna impedances, calculated on the basis of a cold, magnetized plasma model and a warm, nonmagnetized, collisionless plasma sheath model, are compared with the data, showing that the sheath model is more appropriate. The response of the electric field antenna to constant onboard sources of electromagnetic interference is used with the antenna sheath impedance model to calculate plasma densities. The resulting densities are similar to those obtained from OGO 2 plasma density data scaled to the OV3‐3 orbital parameters. The impedance of the TRW Systems Group VLF electric field antenna, also on board OV3‐3, is calculated and compared with the data. It is shown that the sheath antenna impedance model applies equally well to both antennas even though they were quite dissimilar. Much of the signal variation observed by the Aerospace and TRW electric field antennas is caused by antenna impedance changes as a function of local plasma density.

Impedance characteristics of an active antenna at whistler mode frequencies

“…A number of theoretical studies of radiation from a short dipole antenna surrounded by plasma have been carried out starting in the 1960s [e.g., Mlodnosky and Garriott , 1963; Balmain , 1964; Despain , 1966]. The subject was extensively studied in the 1970s [e.g., Koons et al , 1970; Shkarofsky , 1972; Kuehl , 1974; Laframboise et al , 1975; Adachi et al , 1977], and work continued later on until recently [e.g., James , 2000; Nikitin and Swenson , 2001; James , 2003]. While these works have brought a conceptual understanding of the antenna‐plasma interaction, some models often lacked self‐consistency, since in most cases electrostatic conditions were assumed and the radiation resistance was not considered in the system.…”

“…Experimental investigations, however, were rare and were mainly made at the ionospheric heights. They were carried out on board the OV3‐3 spacecraft [e.g., Koons et al , 1970], ISIS satellite [ James , 1980], and also rockets [ Chugunov et al , 2003; James , 2003]. In most cases, the measured voltage or antenna potential as function of operating frequency was compared to those calculated using impedance theories for dipole antenna in plasma.…”

“…In most cases, the measured voltage or antenna potential as function of operating frequency was compared to those calculated using impedance theories for dipole antenna in plasma. It has been demonstrated that an agreement between the observations and theory was reasonably good when the sheath effect is taken into account [e.g., Koons et al , 1970; James , 1980] and that the propagation near the resonance cone requires special treatment [ Chugunov et al , 2003]. Song et al [2007] reported some preliminary experimental results obtained with the RPI‐IMAGE instrument and compared the measurements with their sheath model.…”

Observations of SAR arcs from OV1-10

“…According to the theory of Cornwall et al [1971], ring current energy is dissipated at the plasmapause. If we assume that the arc is generated as a consequence of dissipation of ring current energy [Cole, 1965] The VLF method that 0V3-3 (1966-70A) used to measure the location of the plasmapause has been described by Koons et al [1970]. According to their results the plasmapause was located at L --2.5-2.9 at 0213 LT, 0036 UT on December 16, 1966.…”

The effect of strong pitch angle scattering on the location of the outer-zone electron boundary as observed by low-altitude satellites

“…The data are from the 712-keV electron channel of the OV3-3 (1966-70A) magnetic spectrometer and the 400-Hz frequency band from the electric field antenna on the same satellite. (See Vampola [1969] and Koons et al [1970] for instrumentation details. The geometric factors listed by Vampola [1969] are all a factor of 4 too high owing to an error in the original calculations.)…”