Improving the accuracy of GOCO06s global geoid model on Sardinia Island (Italy) using Ordinary Kriging interpolation in GIS

Abstract. The geoid is the equipotential surface of the Earth's gravity field that best approximates mean sea level. In many applications of geomatics the availability of a geoid model is fundamental as it allows to transform the ellipsoidal heights provided by the GNSS (Global Navigation Satellite System) survey into orthometric heights, i.e. referred to the mean sea level. There are global-scale geoid models, while others exist on a regional scale and are more accurate than the former. Global geoids are generally obtained from measurements of the terrestrial geopotential carried out from space, appropriately integrated with data obtained in situ. This article focuses on the possibility of improving the accuracy of the global model GOCO06s (GOCO is the acronym of Gravity Observation Combination) in a local area, Sardinia Island (Italy), through two operations carried out in Geographic Information System (GIS) and based on the comparison with the local model (at national scale) ITALGEO2005: the removal of the bias found between the two (global and local) models, and the application of the Ordinary Kriging interpolator on the residuals that still remain between the two surfaces compared. The first operation determines a considerable improvement, demonstrated by the RMS value dropping from 1.000 m to 0.365 m. The second operation further increases the accuracy of the model since, with the use of 60 Ground Control Points, an RMS equal to 0.140 m is reached.