Ionosphere TEC Observation Over Ocean Using Single-Frequency Wideband GNSS Signal Reflectometry

This paper presents a preliminary study of a new TEC observation technique by exploiting single-frequency GNSS-R pseudorange measurements (especially from the wideband signal) collected by LEO satellites over equatorial oceans and high latitudes. Pseudorange estimation is more robust compared to that of carrier phase and can be obtained over Earth surfaces with more relaxed smoothness requirements. The GNSS-R pseudorange has contributions from geometric range of the reflection signal path, troposphere delay, satellite oscillator errors, and ionosphere delay. By utilizing precise orbit solutions for GNSS and the low-Earth orbit (LEO) satellites, GNSS satellite clock correction, ocean and sea ice surface height models, troposphere delay models, and by solving for LEO satellite clock offset using direct GNSS signals, we can estimate most of the pseudorange contributors. Then the residual is the measurement of ionospheric delay with some unmodeled/mis-modeled errors and noise. Such measurement can potentially provide ionospheric TEC measurement with an accuracy of a few TECU.