Observation and characterisation of ionospheric scintillation using the Spire radio occultation constellation

Abstract:

Ionospheric scintillation is characterized by rapid variations of a radio signal’s amplitude, phase and direction of arrival due to propagation through small-scale electron density irregularities. The irregularities modify the ionospheric refractive index and cause refractive and diffractive effects that can modify the signal’s properties such as coherence time and bandwidth.

Scintillation can have a significant impact on many technologies that use trans-ionospheric propagation for communication, navigation, surveillance and earth observation. Susceptible technologies include global navigation satellite systems (GNSS) and their associated satellite-based augmentation systems, V/UHF satellite communications, HF communications, UHF early warning radar, and space based synthetic aperture radar (SAR, especially low frequency SAR designed for foliage penetration). The ionospheric refractive index is dependent on the frequency of operation; furthermore, the magnitude of the scintillation effects is determined by the scale-size of the irregularities in relation to the size of the first Fresnel zone. Therefore the scintillation impacts are frequency dependent.

The effects of ionospheric irregularities on trans-ionospheric radio waves are most usually observed in the phase and/or amplitude scintillations of the signal. Many indices have been developed to quantify the magnitude of scintillation events. These include the amplitude scintillation index (S4), the phase scintillation index (SigmaPhi) and the Rate of TEC index (ROTI). Given that the effects of scintillation are frequency, location and solar cycle dependent it remains important to measure such indices not only to establish climatologies, but also to provide real time situational awareness. This paper will describe the use of data from the Spire constellation of radio occultation satellites to detect and characterize scintillation. This can be achieved with both 1 Hz data primarily collected to provide satellite precise orbits and with the high rate (50 Hz) radio occultation data itself.