Chapter 17 - Remote Sensing of Ionospheric Irregularities

Abstract

Earth’s ionosphere plays a crucial role in atmospheric electricity and is an interesting layer to study radio wave propagation or sky wave propagation in space. The space weather activities create changes in the thickness of ionospheric plasma and structure the ionospheric abnormalities, which disturbs communication and navigation systems. To study the ionospheric irregularities instruments like ionosonde, topside sounders, scintillation receivers, airglow observations, and satellites were used in past years. The different signal wavelengths used in different techniques are susceptible to irregularities of different scale sizes. In the beginning, ionospheric scintillations mainly focused on very high frequency (VHF) and Ultra High Frequency (UHF) radio bands, but nowadays global navigation satellite systems (GNSS) have become an important tool to study ionospheric irregularities. The remote sensing method, when applied to study ionospheric irregularities helps in a better understanding of radio communication and navigation systems. This chapter details various remote sensing techniques such as global positioning system, global navigation satellite system-radio occultation (GNSS-RO), communications/navigation outage forecasting system (C/NOFS), Stretched Rohini Satellite Series, Defense Meteorological Satellite Program, and VHF and L-band scintillations to study characteristics of ionospheric irregularities over equatorial and low latitude region. The occurrence probability of irregularities over low latitude is maximum during equinox months and minimum during summer. Scintillation index (S4) ranges between 0.2 and 0.9 for low latitude stations that are of weak scintillations. The spectral index was reported between -2 and -9 with the mean value as -4. The observed characteristics and length of irregularities were of intermediate scale sizes.