Saturday, 29 October 2016

Study of TEC Fluctuation via Stochastic Models and Bayesian Inversion

Our study on GPS total electron content modelling has been published in Radio Science:

Bires, A.L. RoininenB. D. YeshitaM. Nigussie, and H. Vanhamäki (2016), Study of TEC Fluctuation via Stochastic Models and Bayesian InversionRadio Sci.51, doi:10.1002/2016RS005959.

Study of TEC Fluctuation via Stochastic Models and Bayesian Inversion

We propose stochastic processes to be used to model the total electron content (TEC) observation. Based on this, we model the Rate of change of TEC (ROT) variation during ionospheric quiet conditions with stationary processes. During ionospheric disturbed conditions, for example when irregularity in ionospheric electron density distribution occurs, stationarity assumption over long time periods is no longer valid. In these cases, we make the parameter estimation for short time scales, during which we can assume stationarity. We show the relationship between the new method and commonly used TEC characterization parameters ROT and the ROT Index (ROTI). We construct our parametric model within the framework of Bayesian statistical inverse problems and hence give the solution as an a posteriori probability distribution. Bayesian framework allows us to model measurement errors systematically. Similarly, we mitigate variation of TEC due to factors which are not of ionospheric origin, like due to the motion of satellites relative to the receiver, by incorporating a priori knowledge in the Bayesian model. In practical computations, we draw the so-called maximum a posteriori estimates, which are our ROT and ROTI estimates, from the posterior distribution. Because the algorithm allows to estimate ROTI at each observation time, the estimator does not depend on the period of time for ROTI computation. We verify the method by analyzing TEC data recorded by GPS receiver located in Ethiopia (11.6°N, 37.4°E). The results indicate that the TEC fluctuations caused by the ionospheric irregularity can be effectively detected and quantified from the estimated ROT and ROTI values.

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