Project Details
Projekt
Combination of Space Geodetic Techniques with Clock Ties and Atmospheric Ties (COCAT)
Subject Area
Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
Term
since 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 490990195
Project COCAT aims at improving the international terrestrial reference frame (ITRF) through tying space geodetic observations at co-located ground stations via exploiting knowledge of spatio-temporal variations of air's refractive index quantified by numerical weather prediction systems (atmospheric ties) and simultaneously utilizing precise timekeeping and synchronization between frequency standards realized by time coherence observables (clock ties). This approach is motivated by the fact that in adjusting space geodetic observations, coefficients pertinent to the atmospheric delay, the clock stability, and the station displacement are inherently correlated. This fusion strategy will be developed to enhance the state-of-the-art multi-technique combination that is currently achieved through station coordinates (local ties) and Earth rotation parameters (global ties). In Phase 1, we exploit advances in numerical weather prediction models and precise timekeeping and synchronization to perform a long-term combination of GNSS, VLBI, and SLR at the observation equation level. Since more accurate clocks highlight the inconsistencies and the noise induced by atmospheric refraction, particularly by turbulence, within COCAT a consistent and enhanced atmospheric refraction model for all four space geodetic techniques is sought. The technology that enables the proposed combination scheme is at a proof-of-concept stage and not widely available, thus, the work envisaged in COCAT will start with Monte Carlo simulations, involving GNSS, VLBI, and SLR at first, and DORIS at a later stage. To validate these results, real data sets are organized between the co-located systems at Geodetic Observatory Wettzell as well as other fundamental geodetic sites. By the end of Phase I COCAT will have achieved the first multi-year TRF employing local, global, atmospheric, and clock ties to connect GNSS, VLBI, and SLR at the observation equation level. In Phase 2 we exploit the general relativistic time-dilation effect that quantifies the space-time distortion induced by gravity via the realization of long-baseline chronometric levelling, as well as tying ground measurements from different systems employing observations to satellites and between satellites. Project COCAT is indispensable because it improves atmospheric refraction treatment in the single- as well as multi-system solution and assesses the merits from a combination at the observation equation level employing atmospheric and clock ties, thus paving the path towards fully exploiting the merits that stem from introducing time coherence as a new observable.
DFG Programme
Research Units
Co-Investigators
Dr.-Ing. Mathis Bloßfeld; Dr. Mathias Palm; Dr.-Ing. Manuela Seitz; Dr.-Ing. Daniela Thaller
