There is an increasing reliance on Global Navigation Satellite Systems (GNSS) for our communication and navigation requirements. One of the major sources of error for these applications is the ionized part of the Earth's upper atmosphere,i.e. Ionosphere. This book contains a collection of studies aimed at improving our understanding of the various phenomena in the Equatorial Ionosphere Thermosphere System (EITS). The results presented in this book would help shed some light on the EITS response to various geophysical conditions and would be of particular interest to the experts in the navigation industry, researchers specializing in upper atmospheric studies and geospatial positioning systems.