Unifying the three pillars of Geodesy using space ties

Project Information

SPACE TIE

Grant agreement ID: 817919

DOI

10.3030/817919

Project closed

EC signature date 17 December 2018

Start date 1 May 2019

End date 31 October 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 999 563,00

EU contribution

€ 1 999 563,00

Coordinated by

UNIVERSITAET BERN
Switzerland

Periodic Reporting for period 4 - SPACE TIE (Unifying the three pillars of Geodesy using space ties)

Reporting period: 2023-11-01 to 2024-10-31

Summary of the context and overall objectives of the project

The aim of the SPACE TIE project is to use two satellite geodetic techniques, namely Global Navigation Satellite Systems (GNSS) and Satellite Laser Ranging (SLR), to connect the three pillars of Geodesy (“Earth’s space”, “Earth rotation”, “Earth’s gravity field”) by co-location sites in space. These so-called space ties shall be realized on satellites of the currently existing space infrastructure. This includes the Medium Earth Orbits (MEO) of the GNSS satellites and, in particular, satellites in Low Earth Orbits (LEO) with GNSS and SLR co-located on-board.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the project period we focused on tasks covering all four Work Packages. Major achievements were

• the set-up of a full processing chain for the operational provision of GNSS phase bias products needed for undifferenced ambiguity resolution
• studies about the GNSS-based determination of the terrestrial scale via Galileo satellites
• a significant upgrade of the dynamic LEO orbit determination capabilities by using sophisticated non-gravitational force models
• first orbit determinations based on the multi-GNSS data (GPS and GLONASS) of the COSMIC-2 mission launched in 2019 and (GPS and Galileo) of the Sentinel-6A mission launched in 2020 and Spire CubeSat GPS data
• studies about systematic errors in Jason-3 orbit solutions
• the generation of multi-satellite SLR solutions including data of the LARES and LARES-2 satellites
• the set-up of a new normal point generator to analyze full-rate SLR data from spherical satellites
• the study of annual range biases and station coordinate corrections derived from SLR LEO data
• first steps towards a simultaneous estimation of orbit correction parameters from a multitude of LEO satellites tracked by SLR, and the exploitation of GPS-tracked LEO satellites to recover mass variations in the system Earth, including the assessment of the Spire CubeSat GPS data
• the set-up of a most realistic framework to study the challenges of the approved co-location in space mission Genesis in collaboration with the Deutsches Zentrum für Luft- und Raumfahrt (DLR)
• the set-up of a generalized variance component estimation (VCE) scheme for proper stochastic modelling of the GRACE-FO observables, which led to a new release 02 of the AIUB operational GRACE Follow-On monthly gravity field solutions.

In addition, significant efforts have been performed to work towards unifying the two branches of the Bernese GNSS Software related to GNSS analyses and SLR analyses, and to develop a new tool of the Bernese GNSS Software for numerically integrating satellite orbits that will allow for a flexible handling of orbit and gravity field parameters as it will be needed for the SPACE TIE project.

In this context a generalization of the software tools has been achieved to directly use the GPS carrier phase observations for gravity field recovery from LEO GNSS data, which will allow to link the gravity field with the other pillars of geodesy not only for the long wavelength part but also for the medium wavelength part by exploiting the LEO GNSS tracking and the even shorter wavelengths by linking the K-Band inter-satellite tracking of GRACE-FO.

In the frame of the Space Tie project 17 peer-reviewed scientific articles were published and several more are still in the pipeline.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The progress beyond the state of the art is

• the development of GNSS clock products which on the one hand allow single-receiver ambiguity resolution and on the other hand also show best possible consistency to pseudo-range measurements
• the analysis of the GNSS contribution to the determination of the terrestrial scale
• the exploitation of LEO SLR data beyond the usual LEO orbit validation applications towards core geodetic analyses
• recovered mass trends and variations in Greenland and the Amazon River basin from a combination of several LEO satellites tracked by GPS.
• a rigorous multi-GNSS zero-difference processing including ambiguity resolution
• a rigorously combined multi-GNSS processing (including ambiguity resolution) to determine parameters from both terrestrial and spaceborne GNSS data in one and the same parameter estimation process
• the exploitation of homogenously generated SLR normal points from SLR full-rate data to further reduce systematic errors in the SLR data analysis
• the exploitation of LEO co-location platforms in a combined GNSS-SLR processing
• a flexible technical handling of orbit and gravity field parameters in the Bernese GNSS Software.
• the analysis of GNSS observations for the upcoming Genesis mission, which were simulated in collaboration with the Deutsches Zentrum für Luft- und Raumfahrt (DLR) together with GNSS data of the IGS ground station network based on detailed link-budget simulations.

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