Wyniki wyszukiwania - Biblioteka Nauki

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User Interaction and Workflow Management in Grid enabled e-VLBI Experiments

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Dolata Ł. , Okoń M. , Stokłosa D. , Trocha S. , Meyer N. , Stroiński M. , Kaliszan D. , Rajtar T. , Lawenda M.

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tom Vol. 15, nr 1

95-104

EN

The purpose of this paper is to present the design of the integration of radio-astronomical VLBI experiments with the Grid environment. The current status of the VLBI process is described, and the main part of this document presents the proposed architecture for the development of the next generation e-VLBI system. This design was created for the purpose of the EXPReS project [12], partially funded by the European Commission (FP6 – IST).

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Status and prospects for combined GPS LOD and VLBI UT1 measurements

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Senior K. , Kouba J. , Ray

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2010

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tom Vol. 45, No. 2

57--73

EN

A Kalman filter was developed to combine VLBI estimates of UT1-TAI with biased length of day (LOD) estimates from GPS. The VLBI results are the analyses of the NASA Goddard Space Flight Center group from 24-hr multi-station observing sessions several times per week and the nearly daily 1-hr single-baseline sessions. Daily GPS LOD estimates from the International GNSS Service (IGS) are combined with the VLBI UT1-TAI by modeling the natural excitation of LOD as the integral of a white noise process (i.e., as a random walk) and the UT1 variations as the integration of LOD, similar to the method described by Morabito et al. (1988). To account for GPS technique errors, which express themselves mostly as temporally correlated biases in the LOD measurements, a Gauss-Markov model has been added to assimilate the IGS data, together with a fortnightly sinusoidal term to capture errors in the IGS treatments of tidal effects. Evaluated against independent atmospheric and oceanic axial angular momentum (AAM + OAM) excitations and compared to other UT1/LOD combinations, ours performs best overall in terms of lowest RMS residual and highest correlation with (AAM + OAM) over sliding intervals down to 3 d. The IERS 05C04 and Bulletin A combinations show strong high-frequency smoothing and other problems. Until modified, the JPL SPACE series suffered in the high frequencies from not including any GPS-based LODs. We find, surprisingly, that further improvements are possible in the Kalman filter combination by selective rejection of some VLBI data. The best combined results are obtained by excluding all the 1-hr single-baseline UT1 data as well as those 24-hr UT1 measurements with formal errors greater than 5 μs (about 18% of the multi-baseline sessions). A rescaling of the VLBI formal errors, rather than rejection, was not an effective strategy. These results suggest that the UT1 errors of the 1-hr and weaker 24-hr VLBI sessions are non-Gaussian and more heterogeneous than expected, possibly due to the diversity of observing geometries used, other neglected systematic effects, or to the much shorter observational averaging interval of the single-baseline sessions. UT1 prediction services could benefit from better handling of VLBI inputs together with proper assimilation of IGS LOD products, including using the Ultra-rapid series that is updated four times daily with 15 hr delay.

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GENESIS: integracja technik geodezji satelitarnej w przestrzeni kosmicznej

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Nowak A. , Sośnica K.

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tom R. 95, nr 4

21--23

PL

W 2022 roku Europejska Agencja Kosmiczna podjęła decyzję o sfinansowaniu GENESIS - pierwszej misji satelitarnej dedykowanej w całości geodezji. Misja ta będzie posiadała na pokładzie instrumenty do łączenia czterech technik geodezyjnych, które zostaną skorygowane względem siebie za pomocą starannie skalibrowanych centrów fazowych celem wyznaczenia wektorów wiążących w przestrzeni kosmicznej (ang. space ties). Integracja różnych technik geodezyjnych w przestrzeni kosmicznej pozwoli na rozwiązanie problemów związanych z niespójnościami i błędami pomiędzy nimi, a także otworzy nowe możliwości realizacji układów odniesienia. Dzięki temu społeczność naukowa zbliży się do wypełnienia celów Globalnego Geodezyjnego Systemu Obserwacyjnego, czyli dokładności układów geodezyjnych na poziomie 1 mm oraz ich stabilności w czasie o wartości nieprzekraczającej 0.1 mm/rok. Niniejszy artykuł opisuje nowości technologiczne misji GENESIS oraz ich znaczenie w realizacji globalnych ziemskich układów odniesienia w kontekście różnic względem dotychczasowych rozwiązań.

EN

In 2022, the European Space Agency has decided to fund GENESIS, the first satellite mission dedicated entirely to geodesy. The mission will have instruments onboard to integrate four geodetic techniques, which will be corrected against each other using carefully calibrated phase centers to determine space ties. The integration of different space geodetic techniques will resolve inconsistencies and errors between them, and open up new possibilities for realizing reference frames. As a result, the scientific community will come closer to realizing the goals of the Global Geodetic Observing System, i.e. the accuracy of geodetic frames at the level of 1 mm and their temporal stability of no more than 0.1 mm/year. This article describes the technological innovations of the GENESIS mission and their significance in the realization of the global terrestrial reference frames in the context of their differences from existing solutions.

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Global Geodetic Observing System 2015–2018

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Sośnica K. , Bosy J.

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nr 1