DERIVATION OF ORTHOMETRIC HEIGHTS FROM GPS MEASURED HEIGHTS USING GEOMETRICAL TECHNIQUE AND EGM 96 MODEL

Abstract

As a result of wide spread use of satellite based positioning techniques, especially Global Positioning System (GPS), a greater attention has been focused on precise determination of geoid models with an aim to replace the classical leveling with Global Navigation Satellite System (GNSS) measurements. In this research, geometric technique of deriving orthometric height from GPS survey along a profile and the use of EGM 96 geoid model for deriving orthometric height from GPS data (in GNSS solution software) are evaluated. The main focus of this research is to critically examine the potentials of these methods with a view to establishing the optimum technique as an alternative to classical differential levelling. From the results of the research, the standard erros of residuals are 1.453m and 1.450m respectively for EGM 96 model and the geometrical approach. From the graphical representation of the residuals from the two methods, it was observed that the two curves suddenly became sinusoidal from station 9 (corresponding to SB08 in the tables). This similarity pattern of the residuals makes it difficult to draw a conclusive judgment between the two methods examined; however, from the standard errors of residuals, it could be inferred that the geometrical technique gave a better result over EGM 96 model.