Historical Review of Ionosphere in Perspective of Sources of Ionization and Radio Waves Propagation

Abstract

Before the discovery of ionosphere, the electronic communication was not possible at a distance greater than 100 km due to the curvature of Earth; but after its discovery, the ionospheric wave propagation made possible the electronic communication at even more than 3000 km via reflection of radio waves through ionosphere. The ionosphere is electrically neutral, ranging from 50 to 1000 km in altitude and outer limit can exceed to 3000 km depending upon the geo-magnetic activity. High frequency radiations and charged particles from the Sun are the major source of ionization in ionosphere. The disappearance of the lower regions (below or near 100 km) in night is due to the fast recombination rate of molecular ions: nitric oxide (NO⁺), oxygen (O₂) and nitrogen (N₂), while atomic oxygen (O) is dominant at higher altitude (120 km or above) with longer life time making the presence of F2 layer at night. Topside sounding from satellites and vertical sounding from ground based sounders are the two most important active remote-sensing techniques that play key roles in determining the state of the ionospheres. The high frequency (HF) transmissions depend on the electron density in ionosphere. In GPS (Global Positioning System) signal, the carrier signal is of higher frequency as compared to modulating signal, which consequences a greater speed increase ratio in carrier signal, resulting in phase advance and group delay. The monitoring of ionosphere in perspective of space weather is very important for the reliable functioning of HF transmissions and satellite navigation systems.

Keywords: GPS, HF, phase advance, group delay, ionosphere

Cite this Article

Atiq M. Historical Review of Ionosphere in Perspective of Sources of Ionization and Radio Waves Propagation. Research & Reviews: Journal of Space Science & Technology. 2018; 7(2): 28–39p.