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The GPS satellites provide a platform for radio transmitters, atomic clocks, computers and various equipments used for positioning and different military purposes. The applications of GPS have increased vastly as its reliability and performance has become stronger even during adverse space weather conditions. Although the system has improved greatly, still there are a number of error sources which badly degrade the reliability and accuracy of GPS. Therefore these errors need to be corrected in order to use the system for the area of applications that require high degree of accuracy. Among a number of error sources, the ionospheric error constitutes the major part. Like terrestrial weather, ionospheric properties also change from year to year, day to day and even from hour to hour, due to changes in the solar activity level on transient and long term scales. This ionospheric variability under the influence of solar activity affects the ionospheric propagation of electromagnetic waves in a number of ways. The work contained in this book has been carried out with the objective of evaluating the effects of variable ionosphere on the GPS in terms of TEC, scintillation and delay etc.

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Dr. Azad Ahmad Mansoori received Doctorate degree from Barkatullah University, Bhopal in 2015. He was awarded with Maulana Azad National Fellowship by University Grants Commission, Government of India, New Delhi in 2011 for his Ph.D.

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