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Precise Point Positioning (PPP), coupled with the ambiguity resolution (AR) method, has demonstrated substantial potential in fields like agricultural navigation and airborne mapping. However, there remains a notable deficiency in the comprehensive comparative evaluation of its performance when using rapid and real-time satellite products, especially for mass low-cost receivers. Stations equipped with geodetic and low-cost receivers are analyzed in kinematic and static mode. In the kinematic mode, the GPS+Galileo-combined PPP, employing ambiguity fixing with "WHU" rapid products, achieves the highest positioning accuracy of 0.9 cm, 0.9 cm, and 2.6 cm in the North, East, and Up components, respectively. Real-time PPP using "CNT" products attains accuracies of 2.1 cm, 2.7 cm, and 4.8 cm for these components, utilizing GPS ambiguity-fixed PPP. BDS positioning accuracy is inferior to standalone GPS, but improves when the number of visible BDS satellites exceeds 10. Convergence time analysis shows that approximately 38.2 min are required for single GPS or BDS PPP using the "WHU" products and geodetic receivers, which can be reduced to 18.5 min for dual-system combinations and further to 14.8 min for triple-system combinations. The time can be further reduced by ambiguity fixing. In the static mode, multi-GNSS combination does not significantly impact convergence times, which are more influenced by the precision of the products used. Real-time products require approximately 22 min to achieve horizontal accuracy below 0.1 m, while rapid products reach this accuracy within 10 min. For PPP using low-cost GNSS receivers, more than two hours are necessary to achieve an accuracy better than 0.1 m for kinematic PPP, which is considerably longer than the convergence time observed at MGEX stations. However, the accuracy achieved after convergence, as well as the performance of static PPP, is comparable to that of MGEX stations. [ABSTRACT FROM AUTHOR]

The water vapor content in the atmosphere is highly correlated with rainfall events, which can be used as a data source for rainfall prediction or drought monitoring. The GNSS PPP (Precise Point Positioning) technique can be used to estimate the troposphere ZWD (Zenith Wet Delay) parameter which can be converted into precipitable water vapor (PWV). In this study, we first investigate the impacts of the weighting strategies, observation noise settings, and gradient estimation on the accuracy of ZWD and positions. A refined strategy is proposed for the troposphere estimation with uncombined raw PPP model, down-weighting of Galileo/GLONASS/BDS code observation by a factor of 3, using a sine2-type elevation-dependent weighting function and estimating the horizontal gradients. Based on the strategy, the correlation of the estimated tropospheric parameters with the rainfall is analyzed based on the data from the "7.20" rainstorm in Henan Province, China. The PWV is first calculated based on the hourly global pressure and temperature (HGPT) model and compared with the results from ERA5 products. Results show their good consistency during the rainfall period or the normal period with a standard deviation of 3 mm. Then, the high correlation between the PWV and the heavy rain rainfall event is validated. Results show that the accumulated PWV maintains a high level before the rainstorm if a sustainable water supply is available, while it decreased rapidly after the rainfall. In comparison, the horizontal gradients and the satellite residuals are less correlated with the water vapor content. However, the gradients can be used to indicate the horizontal asymmetry of the water vapor in the atmosphere. [ABSTRACT FROM AUTHOR]

Investigations have been focused on improving the precision of real-time GNSS satellite clock corrections. There is a little literature analyzing the characteristics and impacts of the clock datum and initial clock biases (ICBs). We illustrated the clock anomaly caused by the two factors and proposed a new strategy flexible for global and regional clock estimation based on the mixed-difference observation method. First, we analyzed the clock datum of the final and real-time clocks. Results show that the variation in the clock datum can be up to 500 ns per day depending on the datum definition strategy. The variations can lead to large inconsistencies in the datum for the re-convergence of estimated satellite clocks when using the mixed-difference clock estimation method. To resolve the problem, we propose a new method for the epoch-by-epoch datum definition, which can screen out any outliers in broadcast ephemeris in real time, and particularly suitable for the real-time clock estimation. Second, we analyzed ICB jumps in real-time clock corrections, which can degrade the accuracy of precise point positioning. We propose a short-term prediction of clock corrections for bridging ICBs with the precision better than 0.1 ns for stable satellite clocks within a gap of 1–3 min. The prediction can decrease the magnitude of ICB jumps and thus improve a user solution. Considering the prediction of clocks, high precision cannot be guaranteed for all conditions, we thus recommend broadcasting a discontinuity flag for real-time service, so the re-convergence of ICB can be identified by users for resetting carrier-phase ambiguities. [ABSTRACT FROM AUTHOR]