Assessing the consistency of the CORS Networks in Uganda
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Many governments and organizations have established CORS systems to mitigate atmospheric and orbital errors using error models in their networks. In Uganda, three CORS network systems, EagleCORS, Survnet and UGRF currently operate providing precise, real time 3D coordinates useful for cadastral surveying and mapping. Gaining maximal benefit from these networks would necessitate the synergism of UGRF, EagleCORS and Survnet CORS network systems in Uganda to be realised. This study ascertained the limits to which the coordinates of the CORS are consistent within each individual network and also determined whether the coordinates of CORS stations in one network are consistent with coordinates in another network. The CORS networks were subdivided into smaller manageable networks with an approximate maximum baseline length less than 150km. Rinex data spanning 4-9days were downloaded from EagleCORS, Survnet and UGRF stations. This data was analysed in teqc and also checked for completeness before processing in Trimble Business Centre v.5.00 using precise ephemeris. The resultant coordinates were then compared with the official published coordinates of these stations. The consistency of UGRF coordinates was determined to be between 1mm-5mm. Meanwhile, the consistency of EagleCORS and Survnet stations’ coordinates were determined to exist within a smaller geographical area with a RMSE below 2cm. However, UGRF, EagleCORS and Survnet stations when combined in a single network produce a variation of over 5m. Therefore, it can be considered that the three networks as it is are not consistent. Combining them would necessitate re-computing their coordinates in a new datum for example ITRF 2005. The study also illustrated that the accuracy of GNSS coordinates increases with increase in occupation time and is independent of the baseline lengths between the stations for occupation time spanning 4 hours or longer.