Speaker
Description
Total Electron Content (TEC) measurements derived from Global Positioning System (GPS) signals have become indispensable for application-driven ionospheric characterization, detection and characterization of “weak ionospheric signals” resulting from seismic and weather activities, underpinning the accuracy of satellite navigation, space weather forecasting, and ionospheric corrections in communication systems. Therefore, scrutiny of the precision of GPS-derived TEC is essential. Suppose all error sources are accurately identified and accounted for, code-based TEC determinations provide an absolute measure of TEC, albeit with modest precision, due to significant measurement noise and multipath errors where as carrier-phase observations are far more precise, but inherit an unknown integer ambiguity. The precision of GPS-derived TEC depends on careful mitigation of several error sources and two significant assumptions. A primary factor is the differential code bias (DCB) whose magnitude can reach several to tens of nanoseconds (equivalent to many TECU), making them a significant error source if uncalibrated. Modern TEC processing thus relies on robust bias calibrations, often using global networks and stable reference models, to remove these inter-frequency biases. Another major concern is multipath and measurement noise, which predominantly affect code measurements. Improved antenna design and receiver technologies have helped minimize the impact of multipath, but residual multipath can still limit precision in degraded signal environments.
Most previous efforts on determining the precision of TEC measurements have focused on the hardware and DCB, with very little attention given to the assumptions on the ionospheric condition made in estimating the TEC. Two primary considerations were made in the estimation of TEC using GPS observables: a) the ionosphere is purely refractive, and b) higher-order effects. The effect of these two considerations was never scrutinized in the precision of the TEC estimated using GPS observables. In this study, we examine the effect of these two considerations on the relative TEC precision using high-data-rate (100 Hz) phase observables of L1, L2, and L5 frequencies. The ionospheric conditions under which the precision deteriorates will be discussed.
| Keyword-1 | TEC |
|---|---|
| Keyword-2 | Ionosphere |
| Keyword-3 | Precision |