Determination of horizontal displacement in a part of Sudan conventional triangulation network using GNSS

We use satellite positioning measurements based on global navigation satellite systems (GNSS) to determine the horizontal displacements over the old triangulation network. The study area is located in Merowe Dam area in the Northern State of Sudan. The validation process starts by correcting the control points relative to GNSS reference system. The triangulation method is based on angle measurements between the points by optical theodolites. Therefore, it is suitable for the comparison with GNSS more than other conventional methods because there is no distance or scale inconsistencies occur during the triangulation measurements. The quality of the network baselines has been evaluated using the ratio-test criterion and root mean square (RMS). The cut-off ratio was set for values equal or greater than 1.5, however, small values have shown a good quality as well. RMS shows the high quality of the measurements over the entire network with maximum RMS of less than 2 cm. The average horizontal displacement in the control points is 8 mm to the East direction and 1.8 cm in the North direction. The final results show that there is an average displacement of about 60 cm in the horizontal direction. The study further warns that more careful and regular measurements are to be considered for monitoring the displacement occurs in the network.