Investigation of the reliability of variance-covariance matrix in GPS precise point positioning

Precise Point Positioning (PPP) technique is one of the most important subjects in Geomatic Engineering. PPP technique needs only one Global Navigation Satellite Systems (GNSS) receiver thus users have preferred it instead of traditional relative positioning technique for several applications. Scientific softwares have been used for PPP solutions and the Variance-Covariance (VCV) matrices estimated from these softwares may be very optimistic. The formal errors (VCV matrices) have major effects on statistical interpretation. Variance-Covariance (VCV) matrix derived from GNSS processing software plays important role for deformation analysis and scientists sometimes need to scale VCV matrix. In this study, 10 continuously operating reference stations have been considered for 11 days dated 2014. All points have been analyzed by GIPSY-OASISII v6.4 scientific software. The solutions were derived for different session durations as 2, 4, 6, 8, 12 and 24 hours to obtain repeatability of the coordinates and analyses were carried out in order to estimate scale factor for the PPP results of GIPSY-OASIS II v6.4. According to the results scale factors slightly vary depending on the raises in respect of session duration.