Ionospheric Modification by Chemical Releases and High Power Radio Waves


Book Description

Ionospheric plasma density irregularities can be produced locally by chemical releases from space vehicles or remotely by a beam of high power radio waves transmitted from the ground. F-region plasma modification occurs by (1) chemically enhancing the electron number density, (2) chemically reducing the electron population, or (3) physically convecting the plasma from one region to another. The three processes (production, loss, and transport) can determine the effectiveness of ionospheric chemical releases and high frequency electromagnetic wave transmissions in subtle and surprising ways. Initially, a chemical release produces a localized change in plasma density and high power radio waves heat the electrons to yield enhanced transport from pressure gradients in the heated region. Subsequent processes, however, can lead to enhanced transport in chemically modified regions and modified reaction rates in the regions affected by high power radio waves.




Ionospheric Modification and Its Potential to Enhance Or Degrade the Performance of Military Systems


Book Description

The propagation medium is, in effect, an integral part of many military systems. For the most part, interest in the propagation medium has been focussed [sic] on identifying and quantifying the limitations it imposes on systems, rather than on ways it might be altered, or controlled. The results of on-going theoretical and experimental research show potential for modifying selected regions of the ionosphere in order to affect radio wave propagation. A variety of modification techniques are being investigated, both ground- and space-based, to increase or decrease existing ionization or to create independent artificial plasmas. These techniques include high power radio waves, lasers, particle beams, and chemical releases. In addition, recent developments in high power RF sources raise concerns over system limitations due to self induced anomalous absorption, ray path deviation and clutter. These proceedings present the current state of ionospheric modification technology, with emphasis on potential applications for enhancing or degrading the performance of military communications, surveillance and navigation systems.




Ionospheric Modification by High-power Radio Waves


Book Description

Powerful, high-frequency radio waves have been used to temporarily modify the ionosphere. Thermal and parametric interactions have led to a diverse range of observed phenomena, including generation of density striations and artificial spread-F, enhancements of electron plasma waves, production of extrathermal electron fluxes and enhanced airglow, modification of the D-region temperature and densities, wideband signal attenuation, and self-focusing and scattering of the electromagnetic waves. The physics of ionospheric modification by high-power radio waves is reviewed in the context of our current theoretical understanding; disturbance generation mechanisms are qualitatively described. In addition, results of recent experiments are summarized in which ionospheric irregularities are generated and their evolution and decay processes investigated in detail. The effects and potential controlled applications of these HF ionospheric modifications for various RF systems studies are discussed. The C3I scientific community provides an important motivation for these ionospheric modification studies; their increased interaction and active participation in experimental design and interpretation are encouraged.



















Preliminary Investigation of Ionospheric Modification Using Oblique Incidence High Power HF Radio Waves


Book Description

A special experiment was carried out using a high powered transmitter and a high gain rhombic antenna to heat the ionosphere at a distance of 1300 km from the transmitter. A Digisonde ionospheric sounder was located at the midpoint to sense any changes that might occur in the ionosphere at the heating cycle period of ten minutes. The measured phase data was processed using spectrum analysis in an attempt to detect this ten minute period. The results are not conclusive but there is some indication that the heating period was detected only during the nighttime in agreement with theoretical prediction. Keywords: Ionosphere; Modification; High frequency; Propagation.