New receiver bias calculation for total electron content (TEC) in Bangkok, Thailand

Abstract

Ionospheric delay is an important parameter which affects the positioning accuracy of Global Navigation Satellite System (GNSS). It can be analyzed from the total electron content (TEC) in the signal propagation path, computed from the code and carrier phase of at least dual-frequency GNSS signals. Although TEC models have previously been developed by several models including the Global Ionospheric Map (GIM), International Reference Ionosphere (IRI) and Klobuchar model for equatorial region, the estimation of TEC may not be as accurate as in other regions due to relatively fewer research studies as well as unique ionospheric characteristics at these latitudes. Generally, computed slant TECs need to be adjusted for satellite and receiver biases, the latter is dependent upon receivers and receiver location. Therefore, this study proposed the new receiver bias calculation algorithm which can deal with these problems including cycle slips, outlier data, and missing data. In particular, the TEC is computed from code pseudo range only, while the receiver bias is computed from both code and carrier phase together with the elevation angle restriction above 60 degrees (to reduce the cycle slip issue). To verify the proposed algorithm, TEC values at KMIT station (latitude =13.73°, longitude =100.77°), located in an equatorial region, in 2016 are estimated during 4 seasons. The TEC results are with those of International GNSS Service (latitude =13.74°, longitude =100.5°) and the global ionospheric map (at grid position: latitude =13.7°, longitude =100°) based on the Root Mean Square (RMS) error. The results evidently demonstrated that the averages of RMS are 20.60% and 10.99% for GIM and IGS, respectively.