Abstract
The time-varying characteristic of the bias in the GPS code observation is investigated using triple-frequency observations. The method for estimating the combined code bias is presented and the twelve-month (1 January–31 December 2016) triple-frequency GPS data set from 114 International GNSS Service (IGS) stations is processed to analyze the characteristic of the combined code bias. The results show that the main periods of the combined code bias are 12, 8, 6, 4, 4.8 and 2.67 h. The time-varying characteristic of the combined code bias, which is the combination of differential code bias (DCB) (P1–P5) and DCB (P1–P2), shows that the real satellite DCBs are also time-varying. The difference between the two sets of the computed constant parts of the combined code bias, with the IGS DCB products of DCB (P1–P2) and DCB (P1–P2) and the mean of the estimated 24-h combined code bias series, further show that the combined code bias cannot be replaced by the DCB (P1–P2) and DCB (P1–P5) products. The time-varying part of inter-frequency clock bias (IFCB) can be estimated by the phase and code observations and the phase based IFCB is the combinations of the triple-frequency satellite uncalibrated phase delays (UPDs) and the code-based IFCB is the function of the DCBs. The performances of the computed the IFCB with different methods in single point positioning indicate that the accuracy for the constant part of the combined code bias is reduced, when the IGS DCB products are used to compute. These performances also show that the time-varying part of IFCB estimated with phase observation is better than that of code observation. The predicted results show that 98% of the predicted constant part of the combined code bias can be corrected and the attenuation of the predicted accuracy is much less evident. However, the accuracy of the predicted time-varying part decreases significantly with the predicted time.
Highlights
There are biases between Global navigation satellite system (GNSS) different observations due to effects of space environment and frequency-dependent signal hardware delays at the satellite and the receiver
The GNSS biases are generally analyzed and investigated based on the redundant observations and the geometry-free observations. They can be classified into two types of code and phase observations and have obtained much attention from many authors and this area of research has deeply developed in recent years [1]
Some of the time-varying biases are noticed as the cognition of GNSS and its observations deepen in recent years
Summary
There are biases between Global navigation satellite system (GNSS) different observations due to effects of space environment and frequency-dependent signal hardware delays at the satellite and the receiver. The ionosphere model parameters are estimated using the raw observations based precise point positioning (PPP) [7] In this method, the phase and code observations are used to estimate the ionosphere model parameters, but the receiver DCB (P1–P2) was just computed and the satellite DCB (P1–P2) was corrected using International GNSS Service (IGS) [8] products. The biases, especially the time-varying bias, in the code observation affect the accuracy of the code observation and the high-quality float ambiguity solution This requires rigorous modeling of all error sources affecting carrier phase and code observations in PPP data processing, and the corresponding bias should be precisely calibrated for code-based positioning [17,18,19], timing [20], and ionosphere modeling [21,22,23].
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