Comparison of the qualities of recent global and local gravimetric geoid models in Iran

Abstract

A number of regional gravimetric geoid models have recently been determined for the Iran area, and a common problem is to select the best model, e.g. for engineering applications. A related problem is that in order to improve the local geoid models, the selection of the best Global Geopotential Model (GGM) model for the region is essential, to be used in a combined solution from GGM and local gravimetric data. We discuss these problems by taking advantage of 260 GPS/levelling points as an external tool for validation of different global and local geoid models in the absolute and relative senses. By using relative comparisons of the height differences between precise levelling and GPS/geoid models we avoid possible unknown systematic effects between the different types of observables.The study shows that the combination of the newly released GRACE model (GGM02C) with EGM96 geoid model fits the GPS/levelling data in Iran with the best absolute and relative accuracy among the GGMs. Among the local geoid models, the newly gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models. Its rms fit with GPS/levelling is 55 cm. Hence, we strongly recommend the use of this new model in any surveying engineering or GPS/levelling projects in the area.

GNSS in Practical Determination of Regional Heights

“…In these cases, one may resort to applying global geopotential model values (Equation 4) that best fit the gravity field of the region. Determining the optimal global model for either, using the base model in R-R construction of the regional geoid or estimating the geoid undulations in the region with a relatively low accuracy, it will be necessary to undertake a comparison and validation of the models with independent geoid and gravity information, such as GNSS/levelling heights and gravity anomalies Kiamehr & Sjöberg, 2005;Merry, 2007).…”

The Evaluation of High-Degree Geopotential Models for Regional Geoid Determination in Turkey

“…Due to their optimism, the quality estimates are not used as performance indicators of GGMs in a particular area. Therefore, private reliability-precision validations should be executed by the users of GGMs (Kiamehr and Sjöberg, 2005). The sustained advancements in the acquiring, understanding, and modelling of GNSS data have ensured geodesists with accurate and precise exterior control for evaluating global-regional gravity field models of the Earth (Kotsakis, 2008).…”

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.…”