A three-dimensional ionospheric electron density (Ne) model has been named the TaiWan Ionospheric Model (TWIM) and constructed from global distributed ionosonde foF2 and foE data and vertical Ne profiles retrieved from FormoSat3/COSMIC GPS radio occultation measurements. The TWIM exhibits vertically-fitted α-Chapman-type layers, with distinct F2, F1, E, and D layers, and surface spherical harmonics approaches for the fitted layer parameters including peak density, peak density height, and scale height. These results are useful in investigation of near-Earth space and large-scale Ne distribution. We have also developed a time series autoregressive model to forecast short-term TWIM coefficients. The time series TWIM coefficients are considered as realizations of stationary stochastic processes within a processing window of 30 days, and their autocorrelation coefficients are used to derive the autoregressive parameters and then forecast the TWIM coefficients based on the least squares method and the Lagrange multiplier technique. The forecasting root-mean-square relative errors of TWIM coefficients are generally <30% in one-day prediction. In this research, based on the developed real-time TWIM we propose to (1) improve GPS positioning by correcting ionospheric delays on both single-receiver and double-receiver L1 GPS code measurements, (2) predict GPS/GNSS signal unlocks because of ionospheric Ne irregularities, and (3) further improve the TWIM.
|Effective start/end date||1/08/15 → 31/07/16|
- Ionospheric model
- GPS/GNSS positioning
- GPS/GNSS signal unlock
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