Determination of Orthometric Heights of Points Using Gravimetric/GPS and Geodetic Levelling Approaches

The importance of practical, as well as orthometric heights in engineering cannot be underestimated as it is required for the determination of proposed construction levels and to direct the flow of water. This study presents the determination of orthometric heights of points using gravimetric/GPS and geodetic levelling approaches and compares the resolution of the two approaches to determine which of the methods is better for orthometric height determination in the study area. A total of 59 stations were occupy for gravity observation using Lacoste and Romberg (G-512 series) gravimeter to obtain the absolute gravity values of the points. GNSS observation was carried out in static mode using South GNSS receivers to obtain the positions and ellipsoidal heights of the points. The modified Stokes' integral was applied to obtain the geoid heights of the points. Similarly, levelling was carried out using the geodetic level to obtain the level heights of the points. The orthometric correction was applied to the geodetic levelling results to obtain precise level heights of the points. The RMSE index was applied to compute the accuracy of the geoid models. The computed result shows that orthometric heights can be obtained in the study area using the two models with an accuracy of 0.3536m. Z-test was carried out to determine if there is any significant difference between the two methods. The test results show that statistically, there is no significant difference between the two methods. Hence, the two methods can be applied for orthometric heights determination in the study area.