Homogenizing coordinates through the use of the active CORS in Ghana

Abstract

In this study, the course towards determining the homogeneous three-dimensional (3D) coordinates of the newly established active Continuously Operating Reference Station (CORS), based on ITRF2014 in Ghana, is revealed. The aim is to address coordinate inconsistencies and inhomogeneity in the published positions of the new active CORS in Ghana. In order to attain homogeneity, the coordinates of two primary control points, GCS 305 and GCS 306, were obtained using AUSPOS online services via email. These were subsequently used as reference stations to compute the position of the LISAG_KUMASI CORS. Adjustments to the position coordinates were performed using Topcon Tools v8.2.3 software at a 1mm standard deviation.  The adjusted coordinates of LISAG_KUMASI were used as the reference points to compute the positions of the LiSAGNet CORS in differential mode by using 24 hour data for 11 consecutive days. The GPS data covered DoY 284 to DoY 295 in 2021. The final positions of the CORS, computed by this approach, indicate some differences from the officially published coordinates of the same CORS, confirming the suspicion of inhomogeneity in the source coordinates used in determining the coordinates of the local CORS. Furthermore, a test network, consisting of five COR stations, was designed and used to address the coordinate inconsistencies in the officially published coordinates. Using the officially published coordinates as reference inputs, the ROVER I station was fixed by three different CORSs, thus resulting in average coordinate variabilities of 2.78m and 0.80m in the northing (N) and easting (E) directions, respectively. Through substitution, the coordinates computed in this study as reference inputs, namely, the ROVER I station, were fixed by the same three CORSs, thus resulting in a coordinate variability of 0.002m and 0.006m in the northing (N) and easting (E) directions, respectively. The analysis revealed inconsistencies and inhomogeneity in terms of the officially published coordinates. It is, therefore, recommended that the officially published coordinates of the CORS be replaced by the adjusted homogeneous and consistent values determined through the approach adopted in this study.