| Summary: | The continuity and accuracy of real-time (RT) global satellite navigation system (GNSS) sensing of atmospheric water vapor can be seriously affected by a lack of connectivity. To mitigate this issue, a method has been developed that utilizes the International GNSS Service (IGS) ultrarapid satellite orbit and an established RT service (RTS) for satellite clock correction. This method ensures the accuracy of RT atmospheric water vapor estimation even when communication is interrupted. The established RTS utilizes variations in historical clock correction data from the user side to extrapolate its RT high-precision value. Through experimentation, it has been determined that using a quadratic polynomial and an eighth-order harmonic-based function along with 1-h historical clock correction data is optimal for establishing this RTS method. The 2-D and 3-D accuracies of static Precise Point Positioning can achieve centimeter to millimeter levels, and the estimated average root mean square (rms) of zenith tropospheric delay (ZTD) is equivalent to the RT archived products. When compared to the precipitable water vapor results obtained from IGS ZTD products, the averaged rms values of GPS, Galileo, and BDS-3 PWV reach 3.12, 4.41, and 6.43 mm, respectively, which can meet the accuracy requirements of general numerical weather forecasting and other applications during communication interruptions.
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