Verifying the Limitation of GNSS-PPP Derived Orthometric Heights in Engineering Design Using Non-rigorous Approach

Abstract

Height is a vital component in highway construction, vertical and horizontal alignments in structures, deformation monitoring, subsidence analysis and terrain model analysis. GNSS-PPP height is obtained by way of the operations of a single GNSS receiver, orbit and clock data products. The GNSS-PPP operations are conveniently carried out via the internet and e-mail services after RINEX files of observations have been sent to these various PPP platforms. This research aimed to verify the limitation of GNSS-PPP heights in engineering design using non-rigorous approach. The instruments used for this study were Automatic level and its accessories together with GNSS V30 Hi-Target receiver with its accessories. The primary data used for this research were obtained by leveling operations. The secondary data used were two GNSS-PPP coordinates which included the ellipsoidal heights and the geoidal undulation values for the two GNSS-PPP stations. The geoidal undulation values of EGM 2008 were obtained using GeoidEval utility software. The geoid eval computes the geoidal height using interpolation in grid of values. The root mean square (RMS) obtained after every interpolation was within the acceptable range of 1mm. The geographical coordinates of the stations were typed in, sent and within a split of seconds, the Geoid undulation values for the points were obtained. The geoid undulation values were subtracted from the ellipsoidal heights obtained from Global Navigational Satellite System-Precise Point Positioning (GNSS-PPP) observations to obtain the orthometric heights of the two GNSS-PPP points used. The orthometric heights then, served as the reduced level value for a point named “Kogi State Poly 005s” (KSP 005s) during the levelling operation including a fly back leveling. The redundant observations carried out were five (5) in numbers with a mean of 0.0461m and a standard deviation of 0.003m respectively. The results of the observations revealed that height accuracies. At 95% confidence level, the marginal error of the differences is 0.0026. The results of the observations revealed that height accuracies provided by GNSS-PPP cannot be used in engineering applications where high accuracy is required. It is therefore recommended that local geoid be determined by gravimetric method to always check the applicability of EGM 2008.