[1] In this paper we present results of a global gravity field recovery using half a year of CHAMP data. We use the energy integral of the motion of a satellite to transform satellite velocities into values of gravitational potential. The feasibility of this approach has already been demonstrated by several groups, using CHAMP reduced-dynamic orbits. We show, that the potential recovered from this kind of orbits depends on the a priori gravity field used for orbit determination. Thus, it cannot be excluded that errors present in the prior field propagate into the new CHAMP gravity model. It is the intention of this paper to avoid this dependency through the use of kinematic orbits, which are free from prior information. The derived potential model, TUM-1S, is validated by comparison to ground data and by satellite orbit residuals. It is shown to be comparable in quality to other state-of-the-art gravity field models.

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Classical numerical integration methods have been tested for determining the orbit of most recent Low Earth Orbiter (hereafter LEO) satellites. In general, numerical integration techniques for orbit determination are commonly used to fill the gap between two discrete, observed epochs. In this study orbits have been determined using the EGM96 gravity model by the Euler, Runge-Kutta, Bulirsch-Stoer and Adams-Moulton numerical integration techniques among others. This analysis is performed for a LEO, the GOCE, and for medium altitude satellite, one GPS satellite. The orbits are integrated under different assumptions on the roughness of the force model, considering effects of the ellipticity, high order gravity and non-static Earth generated accelerations on the orbit. Keywords orbit integration · LEO · ellipticity · high order gravity · tides · air drag Acknowledgement This work is connected to the scientific program of the "Development of quality-oriented and harmonized R+D+I strategy and functional model at BME" project.

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Kinematic orbits provide a time series of independent positions, which are a good base for gravity field recovery. Gravity field recovery using the energy integral requires numerical differentiation in order to get velocity information for kinetic energy. This paper deals with numerical differentiation methods to test the most effective method for velocity determination of a LEO (Low Earth Orbiter).

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