GNSS OBSERVATIONS TO FIND THE RELATIONSHIP BETWEEN THE GLOBAL DATUM WORLD GEODETIC SYSTEM WGS84 AND THE LOCAL DATUM KARBALA 1979. A CASE STUDY OF ERBIL-DUHOK TERRITORY

Abstract

Over the last few years, the Global Navigation Satellite System GNSS was seen as an innovatory method in the disciplinary of geodetic engineering as compared to other classic measuring methods. It is familiar to everyone that the height acquired from GNSS observations is the ellipsoidal height (h), which is the distance over the vertical to the global datum World Geodetic System WGS84. The value of (h) is endowed with a physical meaning relating to engineering applications for identification of the orthometric height (H), after the conversion from the global datum to the local datum. So far, in the Iraqi- Kurdistan region, there is no specific local datum that can be utilized to identify the exact orthometric height over a local vertical datum. This research aims to define the relationship between the global datum WGS84 and the Iraqi local datum Karbala 1979 based on ellipsoid Clark 1880, through extracting the Digital Terrain Model DTM for both datums in the case study area (Duhok-Erbil territory). The obtained results show that there is a significant change in the relationship between the two datums over the study area, and the difference between them is propagated between (-1.751 m) up to (+4.236 m) along with this territory. It is found that the two surfaces are intersected at the midway approximately, between Erbil and Duhok.