Abstract
The multi-constellation Global Navigation Satellite Systems (GNSS) offers promising potential for the retrieval of real-time (RT) atmospheric parameters to support time-critical meteorological applications, such as nowcasting or regional short-term forecasts. In this study, we processed GNSS data from the globally distributed Multi-GNSS Experiment (MGEX) network of about 30 ground stations by using the precise point positioning (PPP) technique for retrieving RT multi-GNSS tropospheric delays. RT satellite orbit and clock product streams from the International GNSS Service (IGS) were used. Meanwhile, we assessed the quality of clock and orbit products provided by different IGS RT services, called CLK01, CLK81, CLK92, GFZC2, and GFZD2, respectively. Using the RT orbit and clock products, the performances of the RT zenith total delays (ZTD) retrieved from single-system as well as from multi-GNSS combined observations were evaluated by comparing with the U.S. Naval Observatory (USNO) final troposphere products. With the addition of multi-GNSS observations, RT ZTD estimates with higher accuracy and enhanced reliability compared to the single-system solution can be obtained. Compared with the Global Positioning System (GPS)-only solution, the improvements in the initialization time of ZTD estimates are about 5.8% and 8.1% with the dual-system and the four-system combinations, respectively. The RT ZTD estimates retrieved with the GFZC2 products outperform those derived from the other IGS-RT products. In the GFZC2 solution, the accuracy of about 5.05 mm for the RT estimated ZTD can be achieved with fixing station coordinates. The results also confirm that the accuracy improvement (about 22.2%) can be achieved for the real-time estimated ZTDs by using multi-GNSS observables, compared to the GPS-only solution. In the multi-GNSS solution, the accuracy of real-time retrieved ZTDs can be improved by a factor of up to 2.7 in the fixing coordinate mode, compared with that in the kinematic mode.
Highlights
Water vapor, as a fundamental component of the atmosphere, plays a key role in the hydrological cycle and the climate system
The results showed that the water vapor estimates with higher accuracy (1.0–1.5 mm) and stronger reliability could be achieved from the Remote Sens. 2017, 9, 1317 multi-Global Navigation Satellite Systems (GNSS) fusion when compared to the single-system solutions (e.g., Global Positioning System (GPS)-only, Global Navigation Satellite System (GLONASS)-only, and Beidou satellite (BDS)-only)
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Summary
As a fundamental component of the atmosphere, plays a key role in the hydrological cycle and the climate system. Traditional water vapor measurements are mainly provided by the meteorological sensors, such as radiosondes and water vapor radiometers [1,2]. Due to the high spatiotemporal variability of the atmospheric water vapor and limitations of these traditional observing techniques, efforts have been made to obtain reliable and enhanced water vapor observations. Global Positioning System (GPS) meteorology conceived as monitoring the atmospheric water vapor with ground-based GPS receivers was firstly introduced in 1990s [3]. The results demonstrated the capability of GPS for providing water vapor estimates with comparable accuracy to those offered by the meteorological sensors [4,5,6]. The GPS-derived water vapor has its advantages, such as low operational expense, high spatiotemporal resolution, and all-weather availability
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