Assessment of the Accuracy and Consistency of GNSS RTK Measurements Based on Private Continuously Operating Reference Stations (CORS) in Nairobi

Abstract

The advancement of Global Navigation Satellite System (GNSS) technology has enhanced navigation and positioning accuracy, reliability, and availability. In Kenya, private organizations have installed CORS to support positioning and navigation services, allowing users to access GNSS RTK corrections for survey and mapping projects. However, the accuracy and consistency of GNSS RTK measurements from private CORS remain unverified, which this study aimed to address. A study in Nairobi, Kenya, examined the accuracy and consistency of private CORS by comparing GNSS RTK measurements over stable Survey of Kenya (SoK) control points using published coordinates as a reference. Large vertical coordinate value discrepancies (8.5 m - 11 m) and relatively smaller horizontal coordinate value discrepancies (0.3 m - 2.4 m) were observed. The discrepancies arise because the private CORS operate on an independent datum, not integrated with the Survey of Kenya (SoK) geodetic control network. The proximity of control points to CORS (less than 30 km) had minimal impact on measurement accuracy. To ensure accuracy and consistency, it is recommended that private CORS be integrated into the national grid, enhancing the reliability of GNSS RTK measurements for diverse survey and mapping applications. Alternatively, users relying on private CORS must localize or perform a site calibration of their rover receivers using at least three known control points to align their measurements with the National Grid.