Heike Bock

Efficient precise orbit determination of LEO satellites using GPS

Abstract Efficient precise orbit determination of LEO satellites plays an important role for near real-time studies of GPS satellite occultations for meteorological purposes. Precise point positioning for each epoch is one approach to achieve this goal. Using IGS orbits and precise clocks for the GPS satellites the positions are generated by the combination of code derived positions and phase derived position differences. Fitting an orbit based on a physical model to the positions promises to complement a procedure that meets the requirements regarding precision and processing speed. This efficient procedure is tested with data of TOPEX/POSEIDON.

Kinematic and Dynamic Determination of Trajectories for Low Earth Satellites Using GPS

With an increasing number of satellites carrying reliable GPS receivers orbit determination using the high precision and uninterrupted GPS tracking technique gains increasing attention. Different from other approaches for generating kinematic satellite trajectories based on zero- or double-differenced GPS observations the procedure developed at our institute uses zero-differences with differences from epoch to epoch for the phase observable. The approach is very efficient due to the elimination of the phase ambiguities. In addition it includes a sophisticated data cleaning procedure. It may also be applied to objects moving on other than Earth-orbiting trajectories.

Comparison of GOCE-GPS gravity fields derived by different approaches

Several techniques have been proposed to exploit GNSS-derived kinematic orbit information for the determination of long-wavelength gravity field features. These methods include the (i) celestial mechanics approach, (ii) short-arc approach, (iii) point-wise acceleration approach, (iv) averaged acceleration approach, and (v) energy balance approach. Although there is a general consensus that—except for energy balance—these methods theoretically provide equivalent results, real data gravity field solutions from kinematic orbit analysis have never been evaluated against each other within a consistent data processing environment. This contribution strives to close this gap. Target consistency criteria for our study are the input data sets, period of investigation, spherical harmonic resolution, a priori gravity field information, etc. We compare GOCE gravity field estimates based on the aforementioned approaches as computed at the Graz University of Technology, the University of Bern, the University of Stuttgart/Austrian Academy of Sciences, and by RHEA Systems for the European Space Agency. The involved research groups complied with most of the consistency criterions. Deviations only occur where technical unfeasibility exists. Performance measures include formal errors, differences with respect to a state-of-the-art GRACE gravity field, (cumulative) geoid height differences, and SLR residuals from precise orbit determination of geodetic satellites. We found that for the approaches (i) to (iv), the cumulative geoid height differences at spherical harmonic degree 100 differ by only

Kinematic Orbit Determination for Low Earth Orbiters (LEOs)

{\approx }10~\%

The impact of common versus separate estimation of orbit parameters on GRACE gravity field solutions

≈10%; in the absence of the polar data gap, SLR residuals agree by

Comparison of Different Stochastic Orbit Modeling Techniques

{\approx }96~\%