Investigations into the quality of Kinematic PPP in open-sky using final-product APPS free online GPS-alone service

The Global Positioning System (GPS) delivers precise, continuous, and worldwide positioning and timing information based on satellite observations. Nevertheless, reliance on a single GNSS constellation is constrained by satellite geometry and signal availability, which may degrade positioning robustness, particularly in kinematic applications. This limited-scale study investigates the performance of kinematic Precise Point Positioning (PPP) using the free online Automatic Precise Positioning Service (APPS). The APPS platform processes alone GPS observation data and employs state-of-the-art GPS PPP algorithms developed by the NASA Jet Propulsion Laboratory to generate precise positioning solutions. The analysis was conducted under open-sky conditions to eliminate the influence of multipath effects. Dual-frequency GPS data were collected at ten spatially distributed fixed stations in Libya, each observed continuously for 24 hours. The datasets were processed in both static and kinematic PPP modes. Static PPP solutions were adopted as reference coordinates for evaluating the accuracy of the kinematic results. The findings indicate that GPS-alone kinematic PPP processed via APPS provides continuous positioning solutions; however, the achieved accuracy is limited. The Average Absolute Error (AAE) reached 0.42 m, 0.175 m, and 0.485 m in the Easting (E), Northing (N), and Height (H) components, respectively. Corresponding Maximum Average Errors (MAE) were 2.2 m in E, 1.5 m in N, and 2.3 m in H, while the Root Mean Square Errors (RMSE) were 0.50 m, 0.21 m, and 0.31 m for E, N, and H, respectively. Moreover, the proportion of kinematic epochs exhibiting absolute errors exceeding 5 cm in the horizontal components and 10 cm in the vertical component amounted to 64% in E, 38% in N, and 45% in H. Overall, the results demonstrate that the kinematic PPP solutions produced by APPS are comparatively unstable and exhibit lower precision and reliability when contrasted with other free online PPP services, such as CSRS-PPP, which are capable of achieving centimeter-level accuracy in kinematic mode even when relying solely on GPS observations.