Quality Analysis of Global Geopotential Models at 1542 GPS/levelling Benchmarks Over the Hellenic Mainland

Abstract

The aim of this study is to present the results of several 'external' quality tests for the most recent (at the time of writing this paper) global geopotential models (GGMs) using precise GPS and leveled orthometric heights over the area of Greece. The tested GGMs include the GRACE-based combined model GGM03C, the latest EIGEN-type combined models EIGEN-GL04C and EIGEN-GL05C, the ultra-high resolution model EGM08 that was released last year by the US National Geospatial-Intelligence Agency, and also the older NASA/NIMA/OSU's EGM96 model. The evaluation tests are based on comparisons of absolute and relative geoid undulations that are computed from the selected GGMs and the external GPS/levelling data. The test network covers the entire part of the Hellenic mainland and it consists of more than 1500 benchmarks which belong to the Hellenic national triangulation network, with direct levelling ties to the Hellenic vertical reference frame. The spatial positions of these benchmarks have been recently re-determined at cm-level accuracy (with respect to ITRF00) through a nation-wide GPS campaign that was organized in the frame of the HEPOS project. Our results show that the EGM08 model offers a remarkable improvement for the agreement among geoidal, ellipsoidal and orthometric heights in the mainland part of Greece, compared to the performance of other combined GGMs over the same area. Finally, our study gives a preliminary (yet realistic) accuracy assessment for GGM/GPS-aided orthometric height determination, over different baseline lengths, throughout the Hellenic mainland.