Evaluation of NRTK GNSS positioning methods for displacement detection by a newly designed displacement monitoring system

Nowadays, Global Navigation Satellite Systems (GNSS)are widely used for deformation monitoring of structures (dams, skyscrapers, etc.), rail systems and landslides. In this study, a displacement monitoring system was designed to evaluate the precision and accuracy of FKP (Flächen Korrektur Parameter), VRS (Virtual Reference Station)and MAC (Master Auxiliary Concept)Network Real Time Kinematic (NRTK)GNSS methods for determining the vertical and horizontal displacements. For this purpose, the distances (simulated displacements)were measured on the X, Y and h coordinate axes using NRTK methods and Static GNSS Technique and compared with the displacements measured by an interferometer (0.1 mm precision)on this designed system. Displacements measured by using the displacement monitoring system were accepted as true values. In general, NRTK methods provides sufficient precision for determining the displacements respect to displacement monitoring system results. Performance of the FKP correction method is better especially on horizontal axes, while MAC method on vertical. In the overall assessment, average differences of displacements between VRS, FKP and MAC methods and the displacement monitoring system were found 6.8 mm, 5.1 mm and 5.2 mm, respectively. Mean square errors of NRTK method was found 4.7 mm in horizontal and 7.9 mm in vertical for overall assessment.