ABILITY OF THE EGM2008 HIGH DEGREE GEOPOTENTIAL MODEL TO CALCULATE A LOCAL GEOID MODEL IN VALENCIA, EASTERN SPAIN

A new generation of global geopotential models (GGM) is being developed. These solutions offer a the with fully-normalized spherical harmonic coefficients of the Earth's gravitational potential up to a degree greater than 2000 with very low commission errors. This paper analyses the recent Earth Gravitational Model EGM2008, developed up to degree and order 2159 with additional coefficients to degree 2190 and order 2159, which means recovering the gravitational field up to approximately 20 km wavelengths. 223 GPS/levelling points of the new Spanish High Precision Levelling Network in the Valencia region (Eastern Spain) are used as external tool for evaluation in that particular region. The same evaluation has been performed to other different global (EGM96 and EIGEN-CG03C), continental (EGG97), regional (IGG2005 and IBERGEO2006) and local (GCV07) geoid models for comparison purposes only. These comparisons show that EGM2008 is the geoid model that best fits to the GPS/levelling data in that region. Based on these results, EGM2008 GGM is used to determine a new local geoid model in the region of Valencia by means of the remove-restore technique in the scenario proposed by least-squares collocation, in order to check the ability of the EGM2008, as a very high-degree GGM, to calculate a local geoid model in the studied area. The determination is presented step by step in this article, comparing the results of each step with those obtained using the same process but with the global model EIGEN-CG03C, complete up to degree and order 360, that is, a high-degree GGM. These two new geoid models have been analyzed using the 223 GPS/levelling points. The results show that local geoid determination based on EGM2008model gives significantly better lit to GPS/levelling points than any other geoid model in the studied area. However the improvement is not significant with respect to the direct use of EGM2008 without any additional local gravity data. Hence we strongly recommend the use of EGM2008 without applying least-squares collocation in the areas where good ground data were available for the computation of EGM2008.