Co-location of Space Geodetic Techniques on Ground and in Space
Final Report Abstract
The major objective of this research proposal was the identification and reduction of systematic errors in space geodesy techniques. The co-location of the observation techniques SLR, VLBI and GNSS both, on the ground and in space, provided the framework for this objective. We have exploited the intra- and inter-technique observation concepts in order to identify systematic errors. On the one hand, this led to the implementation of a novel station fiducial point common for all techniques, which is not only defined by local ties, but also represented in time. Together with a novel lossless time and frequency distribution system, based on a wide bandwidth mode-locked laser we can now identify subtle systematic errors by closure measurements based on accurately distributed time. Over the course of the project, the time and frequency distribution has been established in major parts and most of the closure measurement concepts have been successfully tested. Some of the approaches, such as the joint observation of GNSS and quasars with the same receiver path have not worked appropriately with the routine S/X-band observation technique. This needs to be revisited when the VGOS broadband operability becomes available. The new methods explored in this project will become available routinely, when the integration of the timing system is complete. On the other hand, the analysis of intra-technique experiments led to a better understanding of systemspecific error sources, biases and delays, where variations were monitored and removed. Regarding the GNSS intra-technique analysis, a tailored parametrisation for the co-located antennas (short baselines) was developed. This method was tested for data collected at several geodetic observatories around the world, to determine the local behaviour of the baselines and in multiple cases the used data spanned up to 17 years. To cope with the challenges of the VLBI intra-technique short baseline analysis, the in-house processing software was upgraded to perform the processing of VLBI observations. With this, the data collected by the co-located telescopes at Wettzell was routinely processed, focussing on the modelling of the clock and the troposphere. These enabled the detailed analysis of both the local tie and the common clock system of the telescopes at the site, providing the tools for the rigorous clock combination of GNSS and VLBI. Finally, in the SLR intra-technique domain, new observation and processing strategies were developed and tested. These included the concept of quasi-simultaneous observations to form single- and double differences of SLR observations, suitable for the precise estimation of geodetic parameters. Both, the parameterisation and processing strategies proposed not only improve the knowledge of the error sources, but also enhance the quality of the estimation of geodetic parameters. These are necessary steps for a rigorous co-location of space geodetic techniques.
Publications
- (2016): Co-location of Geodetic Observation Techniques in Space. Doctoral thesis. Swiss Federal Institute of Technology in Zurich. Department of Civil, Environmental and Geomatics Engineering. Institute for Geodesy and Photogrammetry
Männel, B.
(See online at https://doi.org/10.3929/ethz-a-010811791) - (2016): Ionospheric corrections for single-frequency tracking of GNSS satellites by VLBI based on co-located GNSS. Journal of Geodesy, vol. 90: no. 2
Männel, B. & Rothacher, M.
(See online at https://doi.org/10.1007/s00190-015-0865-6) - (2016): Two-way time transfer via optical fiber providing subpicosecond precision and high temperature stability, Metrologia, 2016, 53, 18
Kodet, J.; Pánek, P. & Procházka, I.
(See online at https://doi.org/10.1088/0026-1394/53/1/18) - (2017): Geocenter Variations Derived from a Combined Processing of LEO and Ground-Based GPS Observations. Journal of Geodesy, vol. 91: no. 8, pp. 933-944
Männel, B. & Rothacher, M.
(See online at https://doi.org/10.1007/s00190-017-0997-y) - The Application of Coherent Local Time for Optical Time Transfer and the Quantification of Systematic Errors in Satellite Laser Ranging, Space Science Reviews, 2017, 214, 22
Schreiber, K. U. & Kodet, J.
(See online at https://doi.org/10.1007/s11214-017-0457-2) - (2018): Assessment of Local GNSS Baselines at Co-Location Sites. Journal of Geodesy, vol. 92: no. 9, pp. 1079-1095
Herrera-Pinzón, I. & Rothacher, M.
(See online at https://doi.org/10.1007/s00190-017-1108-9) - (2018): Co-location of space geodetic techniques carried out at the Geodetic Observatory Wettzell using a closure in time and a multi-technique reference target Journal of Geodesy
Kodet, J.; Schreiber, K. U.; Eckl, J.; Plötz, C.; Mähler, S.; Schüler, T.; Klügel, T. & Riepl, S.
(See online at https://doi.org/10.1007/s00190-017-1105-z) - (2019): Analysis of Single- and Double-Differenced SLR Observations at the Wettzell Observatory. EGU General Assembly 2019. Vienna, Austria
Herrera-Pinzón, I. & Rothacher, M.
(See online at https://doi.org/10.3929/ethz-b-000395177) - (2019): Important Aspects of a Rigorous Combination of Space Geodetic Techniques. EGU General Assembly 2019. Vienna, Austria
Rothacher, M.
(See online at https://doi.org/10.3929/ethz-b-000396065)
