Procedure for the determination of Local Gravimetric-Geometric Geoid Model

As the surface adopted for geodetic computation is a mathematical surface which is different from the physical surface, the geoid adopted as a reference for the vertical coordinate system, the ellipsoidal heights obtained from GPS observation are transformed to practical heights known as orthometric heights. The transformation of the ellipsoidal heights to orthometric heights requires the knowledge of the geoid-ellipsoid separation at the point of observation. Since the geometric method requires the computation of geoid heights of points from GPS observation and geodetic leveling carried out over long distances which are labor intensive and prone to human errors, the accurate geoid heights of the points should be obtained from gravity measurement and a geometric geoid surface fitted to the gravimetric geoid heights. This paper presents detailed procedures for determining local gravimetric-geometric geoid model of an area or a region. The detailed procedures which consist of selection of suitable/evenly distributed points, DGPS and gravity observations of selected points, processing of DGPS and gravity observations, computation of gravimetric geoid heights of the points, fitting of geometric geoid surface to the computed gravimetric geoid heights and computation of accuracy of the geoid model are presented in sequential order.