Breaking the DORIS System Accuracy Limitations Caused by Clocks

• Applicant: Professor Dr. Urs Hugentobler
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540974883

DORIS is a satellite tracking system based on Doppler measurements and is one of the four major space geodetic techniques contributing to the realization of an accurate and long-term stable global reference frame serving as the metrological basis for the monitoring and understanding of change processes in the Earth system. The precision of DORIS is limited by the stability of the involved clocks. The Sentinel-3 and Sentinel-6 satellites now offer novel opportunities for DORIS data analysis as they operate the GNSS and DORIS tracking equipment on the same onboard oscillator enabling to estimate epoch-wise clock corrections using GNSS. Of particular interest is also the tandem phase of 130 days of the two Sentinel-3A and -3B satellites. This project aims to tackle the limitations of DORIS exploiting the opportunities offered by Sentinel-3 and 6 to a maximum. The proposing international team joins profound DORIS and GNSS expertise for this effort. Our recent work (Štěpánek et al. 2020) proves the efficiency of the concept to compute GPS-derived epoch-wise Sentinel-3A and Sentinel-3B satellite clock corrections and introduce them as fixed into the DORIS data processing to investigate the impact of this additional information on DORIS-derived estimated parameters such as satellite orbits, station coordinates, Earth rotation parameters (ERP). We have demonstrated the potential of this approach to study the DORIS ground beacon clocks and the South Atlantic Anomaly (SAA) effect. In this project, we plan to extend the time-series to 5 years for Sentinel-3A and Sentinel-3B and also extend the experiments for Sentinel-6A on Jason orbit and Sentinel-3C (to be launched in 2024). We want to use the Sentinel-3A/3B tandem phase for closure measurements by comparing satellite clock corrections derived from GPS through commonly observed beacons and plan to map the stability of the beacon oscillators throughout the DORIS station network. The Bernese GNSS Software enhanced with DORIS capabilities used by VUTGK and TUM is basically a phase data processing software. Also DORIS observations are processed similarly to phase measurements, but setting up an ambiguity per each two phase observations. Within this project we plan to implement a flexible selection of the number of phase observations per ambiguity, allowing a gradual switch between Doppler and phase data processing. Of interest is the analysis of the impact of using more phase data for the entire geodetic DORIS product suite. As last part of the project, we simulate DORIS as a hypothetical measurement system in which all beacon and satellite clocks can be synchronized for every epoch. Allowing it to process phase observations instead of Doppler observations should render the performance to a similar level as known for GNSS and we want to demonstrate the performance. Finally the simulations will be extended to multi-technique satellites like the Genesis mission.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Partner Organisation: Czech Science Foundation
• Cooperation Partner: Dr. Petr Stepanek, Ph.D.