To meet the demands for the data combination with multiple space geodetic techniques at the observation level, we developed a new software platform with high extensibility and computation efficiency, named space Geodetic SpatioTemporal data Analysis and Research software (GSTAR). Most of the modules in the GSTAR are coded in C++ with object-oriented programming. The layered modular theory is adopted for the design of the software, and the antenna-based data architecture is proposed for users to construct personalized geodetic application scenarios easily. The initial performance of the GSTAR software is evaluated by processing the Global Navigation Satellite System (GNSS) data collected from 315 globally distributed stations over two and a half years. The accuracy of GNSS-based geodetic products is evaluated by comparing them with those released by International GNSS Service (IGS) Analysis Centers (AC). Taking the products released by European Space Agency (ESA) as reference, the Three-Dimension (3D) Root-Mean-Squares (RMS) of the orbit differences are 2.7/6.7/3.3/7.7/21.0 cm and the STandard Deviations (STD) of the clock differences are 19/48/16/32/25 ps for Global Positioning System (GPS), GLObal NAvigation Satellite System (GLONASS), Galileo navigation satellite system (Galileo), BeiDou Navigation Satellite System (BDS), Medium Earth Orbit (MEO), and BDS Inclined Geo-Synchronous Orbit (IGSO) satellites, respectively. The mean values of the $$X$$X and $$Y$$Y components of the polar coordinate and the Length of Day (LOD) with respect to the International Earth Rotation and Reference Systems Service (IERS) 14 C04 products are -17.6 microarc-second (µas), 9.2 µas, and 14.0 µs/d. Compared to the IGS daily solution, the RMSs of the site position differences in the north/east/up direction are 1.6/1.5/3.9, 3.8/2.4/7.6, 2.5/2.4/7.9 and 2.7/2.3/7.4 mm for GPS-only, GLONASS-only, Galileo-only, and BDS-only solution, respectively. The RMSs of the differences of the tropospheric Zenith Path Delay (ZPD), the north gradients, and the east gradients are 5.8, 0.9, and 0.9 mm with respect to the IGS products. The $$X$$X and $$Y$$Y components of the geocenter motion estimated from GPS-only, Galileo-only, and BDS-only observations well agree with IGS products, while the $$Z$$Z component values are much nosier where anomalous harmonics in GNSS draconitic year can be found. The accuracies of the above products calculated by the GSTAR are comparable with those from different IGS ACs. Compared to the precise scientific orbit products, the 3D RMS of the orbit differences for the two Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) satellites is below 1.5 cm by conducting Precise Point Positioning with Ambiguity Resolution (PPP-AR). In addition, a series of rapid data processing algorithms are developed, and the operation speed of the GSTAR software is 5.6 times faster than that of the Positioning and Navigation Data Analyst (PANDA) software for the quad-system precise orbit determination procedure.

Quantifying the atmospheric water balance is critical for the study of hydrological processes in significant regions. This study quantified atmospheric water balance closure at 205 stations in mainland China on a monthly timescale from 2009 to 2018 using datasets from ground- and satellite-based observations and reanalysis data. The closure performances were firstly quantified using the mean and root mean square (RMS) of the residuals, and the possible influencing factors were explored, as well as the influence of different water balance components (WBCs) using different datasets. In the closure experiment using ERA5, the mean and residuals were 6.26 and 12.39 mm/month, respectively, on average, which indicated a closure uncertainty of 12.8%. Using ERA5 analysis as a reference, the closure experiment using different combinations revealed average mean residuals of 8.73, 11.50, and 15.89 mm/month, indicating a precipitation closure uncertainty of 22.0, 23.7, and 24.4% for the ground- and satellite-based observations and reanalysis data, respectively. Two possible influencing factors, station latitude and the climatic zone in which the station is located, were shown to be related to closure performance. Finally, the analysis of the impact from different WBCs showed that precipitation tended to have the most significant impact, which may have been due to larger observation uncertainties. Generally, the atmospheric water balance in mainland China can be closed using datasets from different observational techniques.

Precipitable water vapor (PWV) is a vitally important factor in atmospheric circulation. PWV is significant for forecasting extreme weather and understanding the dynamics of climate change. Comprehensively evaluating the performance of newly proposed remotely sensed water vapor products is crucial for guaranteeing their suitability for futural PWV applications. In this study, the accuracy of the recently established remotely sensed water vapor product from the Visible Infrared Imaging Radiometer Suite (VIIRS) satellite sensor on the Suomi National Polar-orbiting Partnership (SNPP) (VIIRS-PWV) platform within various regions of mainland China was evaluated via the PWV from Global Positioning System (GPS) observations. The GPS-derived PWV from 231 stations of the Crustal Movement Observation Network of China (CMONOC) from 2012 to 2018 was obtained through precise point positioning (PPP) techniques. The results showed that the mean value of the correlation coefficient (CC), the mean bias (MB), and the root-mean-square error (RMSE) between the VIIRS-PWV and the GPS-PWV were 0.92, −1.6 mm, and 4.7 mm, respectively. These values were comparable with the results of the PWV data derived from the Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) products. This indicates that the VIIRS product could provide PWV data with satisfactory accuracy for large-area scientific applications. Moreover, the MB and RMSE of the differences between the GPS-PWV and VIIRS-PWV showed obvious seasonal variations. The VIIRS-PWV generally performed better in winter (with the MB and RMSE values of 0.1 mm and 2.3 mm) than in summer (with the MB and RMSE values of −4.4 and 7.0 mm). Analysis among different regions revealed that the Central South (CS) region of China attained the largest mean RMSE value of 6.3 mm, and the North West (NW) region attained the smallest mean RMSE value of 3.8 mm. In addition, the southern region of China obtained a mean RMSE value of 5.6 mm, while that for the northern region of China was 3.9 mm. This indicates that the VIIRS-PWV has better accuracy within the northern region of China than within the southern region.

In this study, an approach based on precise point positioning (PPP) is proposed for the assessment of global ionospheric maps (GIMs). This assessment is performed by comparing GIMs with vertical total electron content (VTEC) values retrieved using the PPP technique. The results indicate that the CODG, ESAG, WHUG, and CASG ionospheric products underestimate the VTEC values. There is a high level of consistency between all GIMs and PPP-VTEC values during periods of low solar activity. In addition, almost all GIMs exhibit significant discrepancies with PPP-VTEC values over the equatorial ionisation anomaly (EIA) region during periods of high solar activity.

Ionospheric delay is one of the main sources of error in satellite positioning and navigation. Ionospheric broadcast parameters are required to correct for the ionospheric delay, especially in the case of massive single-frequency users. The well-known Klobuchar model has been providing the ionospheric delay corrections for GPS users during the last several decades. For Galileo users, a three-dimensional electron density model (NeQuick G) based on the NeQuick climatological model is used to correct for ionospheric delay. The recently completed Chinese BeiDou Satellite Navigation System (BDS) broadcasts two types of ionospheric models coefficients on different signals. In this article, we propose a simplified worldwide ionospheric model (SWIM) for satellite positioning. By comparison, our SWIM model has better performance than the Klobuchar model in terms of accuracy at both low and high solar activity, and is comparable to the NeQuick G and BDS ionospheric models. At the same time, the SWIM model has high efficiency because of the simple calculation process. It has great potential for ionospheric delay corrections in satellite navigation and positioning.