ResearchResearch Projects
Kinematic GNSS positioning of Low Earth Orbiters (CRC 1128, B03)

Kinematic GNSS positioning of Low Earth Orbiters (CRC 1128, B03)

Leaders:  Prof. Dr.-Ing. Steffen Schön
Email:  schoen@ife.uni-hannover.de
Team:  M.Sc. Christoph Wallat
Year:  2014
Sponsors:  DFG
Is Finished:  yes
More Link https://www.geoq.uni-hannover.de/en/research/b-metrology-and-system-modeling/b03/

Overview

Absolute LEO positioning is necessary to determine the low degree and order terms of gravity fields. Current and future gravity field missions rely on GNSS for this task as an integrated part of the satellite navigation.

Especially GNSS-based kinematic LEO orbit determination is appropriate since no a priori knowledge of the gravity field is needed. However, the current accuracy and reliability of GNSSdetermined LEO orbits is restricted by weak geometry due to the epoch-wise estimation of receiver clocks, the large number of ambiguities to be set-up, and due to remaining systematic like antenna phase center variations (PCV) or near-field multipath. Thus, new concepts and perspectives for precise and reliable LEO positioning should be developed. To this end we can benefit from new technologies currently available, like e.g., ultra-stable clocks, inter-satellite laser links and future receiver types tracking multi-frequency multi-GNSS.

Goals

The project will focus on two approaches to improve the orbit quality for future missions: (i) Taking advantage of new ultra-stable space-qualified clocks, concepts of clock modeling will be investigated, i.e. the receiver clock error is modeled by a low order polynomial rather than estimated every epoch. This will yield a strengthening of the geometry and an improvement in both accuracy and integrity. In addition, multipath and PCV can be better detected and separated from other error sources. (ii) The second approach is the development of the so-called virtual receiver, i.e. the observations from multiple antenna/receivers will be combined into one spacecraft solution. The observations can either be collected by multiple optimally oriented antennas at one spacecraft or different antennas separated over multiple spacecrafts if the inter-satellite link is given. In such a way, more GNSS observations can be tracked, the common field of view is significantly enlarged, yielding a better integrity and better ambiguity resolution thanks to longer visible GNSS satellite arcs. The concepts will be developed in close interaction with the projects B02 B06 and C01. Simulation studies as well as real GNSS data analysis of current and upcoming gravity field missions will be used to demonstrate and validate the concepts.