Accuracy Assessment of Online PPP Services in Static Positioning and Zenith Tropospheric Delay (ZTD) Estimation

Precise Point Positioning (PPP) is a stand-alone positioning technique that is capable to provide real-time centimeter level accuracy for a single receiver using the precise satellite orbit and clock data products. Nowadays, a number of free online PPP processing services have been developed in order to obtain highly accurate coordinates with respect to a well-defined datum. Four examples of these services are: (1) Canadian Spatial Reference System (CSRS-PPP), (2) GPS Analysis and Positioning Software (GAPS), (3) Automatic Precise Positioning Service (APPS) and (4) magicGNSS. This paper aims to investigate accuracy of these four online PPP services in static positioning and zenith tropospheric delays (ZTDs) estimation. To this end, repeatability of these four PPP services is investigated for two International GNSS Service (IGS) stations, namely TEHN located in Iran and SOFI located in Bulgaria, in the period from February 1-15, 2015. The repeatability of horizontal components for APPS, GAPS, magicGNSS and CSRS-PPP services are 3 mm, 5.5 mm, 5 mm and 3 mm, respectively. These values for height components are 5.5, 9.5, 6.5 and 6 mm for APPS, GAPS, magicGNSS and CSRS-PPP services, respectively. Furthermore, for the both IGS stations, the estimated position by using these services were compared with their known coordinates in ITRF2008. The results showed that precision of horizontal components obtained by these online PPP services are at a sub-centimeter level, which is required for many mapping applications. Finally, the ZTDs estimated using four online PPP services were compared for February 1, 2015. Compared with the corresponding values published on the IGS Web site, the precision of ZTDs estimated by APPS, GAPS, magicGNSS and CSRS-PPP are 3 mm, 4 mm, 3 mm and 5 mm, respectively.