Ionospheric Phase Scintillation Estimation from Rate of Change of Total Electron Content Index (ROTI) in Low Latitudes

Ionospheric scintillations are fluctuations in the phase and amplitude of the signals from GNSS satellites occurring when they cross regions of electron density irregularities in the ionosphere and hence can cause significant errors in positioning based on Global Navigation Satellite System (GNSS). Scintillation is usually characterized by amplitude and phase scintillation index (S4 and σφ). However, the specialized receivers that can generate the scintillation indices are not available all around the world, which limits the application of these approaches. In spite of that, there are numerous inexpensive geodetic receivers that are capable of measuring the Total Electron Content (TEC) and Rate of TEC (ROTI). The ROTI is a commonly used measure of ionospheric irregularities level.

In order to overcome this problem, the relationship between ROTI and phase scintillation index σφ has been studied. In the present work is applied a quantitative theorical model developed for ROTI related to the phase structure function. This theorical model is a scaled version of the structure function of phase fluctuations imparted to the wave by the irregularities and relates the statistical measures of TEC fluctuations and ionospheric irregularities of associated scintillations. The present model for ROTI accounts for the dependence on the sampling interval, satellite motion, propagation geometry and the spectral shape, strength, anisotropy and drift of ionospheric irregularities.

The focus of this work is to estimate the ROTI based on data from GNSS receivers located in low latitudes then, the σφ index is calculated using the relationship of ROTI/ σφ. Measured drifts will be used to estimate the effective scan velocity, when it is available. In this work we estimated the error comparing the σφ predictions with the σφ computed from 50 Hz phase samples. In addition, this study evaluates the σφ index estimated using a climatological RISA model for drift, different sampling rates (δt =1 s and δt =10 s), GPS frequencies (L1, L2C and L5).