Comparison among Gravimetric, Astrogravimetric and Astrogeodetic Geoids: Case Study for Austria

<p>It is used to state that all geoid determination techniques should yield to the same geoid if the indirect effect is properly taken into account (Heiskanen and Moritz, 1967). The current study compares different geoid determination techniques for Austria. The used techniques are the gravimetric, astrogravimetric and astrogeodetic geoid determination techniques. The available data sets (gravity, deflections of the vertical, height, GPS) are described. The window remove-restore technique (Abd-Elmotaal and Kuehtreiber, 2003) has been used. The available gravity anomalies and the deflections of the vertical have been topographically-isostatically reduced using the Airy isostatic hypothesis. The reduced deflections have been used to interpolate deflections on a relatively dense grid covering the data window. These gridded reduced deflections have been used to compute an astrogeodetic geoid for Austria using least-squares collocation technique within the remove-restore scheme. The Vening Meinesz formula has been used to compute an astrogravimetric geoid for Austria. Another gravimetric geoid for Austria has been determined in the framework of the window remove-restore technique using Stokes integral with modified Stokes kernel. All computed geoids have been validated using GNSS/levelling derived geoid. A wide comparison among the derived geoids computed within the current investigation has been carried out.</p>

Theoretical frame for the application of IOST in the downward continuation of GOCE SGG data

<p>Within the GeoGravGOCE project, funded by the Hellenic Foundation for Research Innovation, one of the main goals is the investigation of downward continuation schemes for the GOCE Satellite Gravity Gradiometry (SGG) data. It is well known that once the original SGG observations have been filtered to the GOCE Measurement Band Width (MBW), in order to remove noise and long-wavelength correlated errors, a crucial point for gravity field and geoid determination refers to the combination of GOCE data with local gravity field information. One possible way to exploit GOCE data is to use them in a Spherical Harmonic Synthesis (SHS) to derive a GOCE-only and/or a combined Global Geopotential Model. Our aim is to overcome the inherent smoothing of SHS and use directly the SGG data in order to investigate their contribution to regional gravity field and geoid determination. For that, methods based on the input-output-system-theory (IOST) are used for the combination of heterogeneous data at the Earth’s surface and at the satellite altitude or a mean sphere. The GOCE Level 2 gradients are first processed, transformed and reduced to a mean orbit using the IOST methods and then are downward continued to the Earth’s surface with an iterative Monte Carlo method (simulated annealing - SA). In this work we present the theoretical background of the proposed methodology and key-concepts for its implementation.</p>