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 GeospatialIntelligence 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.

Evaluation of GOCE/GRACE Derived Global Geopotential Models over Argentina with Collocated GPS/Levelling Observations

“…Some other, possible choices for the height combination problem, are to model the differences with a simple bias ( ) and two scale (ıs H and ıs N ) factors. These models correspond to a height-dependent corrector surface in terms of the generalized equation (Kotsakis and Katsambalos 2010):…”

High-frequency analysis of Earth gravity field models based on terrestrial gravity and GPS/levelling data: a case study in Greece

“…An evaluation of global gravity models over Greece can be found in Kotsakis and Katsambalos (2010), Vergos et al (2012), etc.…”

Improving EGM2008 by GPS and leveling data at local scale

“…Several approaches are used to establish such a geoid in practice. In recent applications, approaches were adopted to determine long wavelength effects utilizing the earth's potential coefficients, medium wave length effects utilizing gravity, and short and ultra-short wavelength effects utilizing combined methods (KIAMEHR, andSJOBERG 2005, BENAHMED DAHOA et al 2006;FEATHERSTONE and SPROULE, 2006;KOTSAKIS and KATSAMBALOS, 2010) Particularly, following the improvements on GNSS (Global Navigation Satellite Systems) technology, the researches focusing on obtaining "cm" level geoid accuracy attracts attention in the 2000's. The geometric modeling with GPSleveling method come to the fore in studies for the determination of short and ultrashort wavelength components of geoid in those years (IAG,1995;OLLIKAINEN, 1997;SOYCAN and SOYCAN, 2003;SOYCAN, 2006).…”

“…Several studies have carried out by researchers for the improvement of global geoids using GPS and leveling data in technical literature and the successful results obtained (KIAMEHR, andSJOBERG 2005, BENAHMED DAHOA et al 2006;FEATHERSTONE and SPROULE, 2006;KOTSAKIS and KATSAMBALOS, 2010;EROL et al 2008;ABBAK et al 2012). It can be concluded from these studies; there are several methods available, such as least squares adjustment with a four, five or seven parameter transformation model, least squares or robust estimations with polynomial models, least squares collocation, finite element method (FEM), the Fourier series, the continuous curvature splines in tension and other interpolation methods.…”