Verknüpfung der kinematischen und dynamischen Referenzrahmen (D-VLBI)
Zusammenfassung der Projektergebnisse
In project “Ties between kinematic and dynamic reference frames (D-VLBI)” we have investigated how the technique of differential VLBI observations can be applied to near-field spacecraft, where Geocentric parallax, significant non-sidereal motion, and near-field delay models require significant changes to standard, far-field, differential VLBI observation and analysis methods. By differencing observations of the VLBI delay of a spacecraft from the VLBI delay of angularly-nearby calibration quasars on the sky, thereby canceling to a great extent measurement errors caused by mismodeling of VLBI antenna positions, clock offsets, atmospheric delays, and so on, the position of the spacecraft relative to that of the quasars can be determined with very high accuracy. We have developed software to enable us to automatically plan and schedule D-VLBI observations of near-field, including Earth-orbiting, spacecraft. For far-field D-VLBI, the (effectively) fixed position of the target and the same celestial viewing geometry for all stations allow the D-VLBI scheduling to be planned manually, but in the near-field case stations can have greatly different viewing geometries, requiring multiple calibrator targets to be selected and scheduled, and fast-moving spacecraft require new calibrators to be selected as rapidly as each scan, thus necessitating that routine near-field D-VLBI observations be planned automatically. Our software has been successfully demonstrated to be able to plan such observations and schedule the observation instructions for individual stations in a way that enables all VLBI stations with a standard Field System interface to be utilized. We have participated in scheduling and analyzing several standard VLBI and differential VLBI experiments to observe near-field spacecraft including GNSS spacecraft. Although the observations were successfully scheduled and executed at the stations, the D-VLBI measurements of GNSS spacecraft were not successful, primarily because the L band receivers at VLBI stations have not been designed to cover the frequency regions of GNSS L band transmissions. “Traditional” VLBI observations have been successfully demonstrated, partially because the extremely high signal strengths (by quasar VLBI standards) of the GNSS targets enables such signals to be detected even when the frequencies are in regions where the VLBI receivers have poor performance. However, D-VLBI observations involving comparisons to nearby quasars have failed to provide suitable results in our GNSS proof-of-concept observations to date because the L band receivers at the astronomical VLBI stations we have so-far utilized have been unable to detect the angularly-nearby quasar calibrator signals, typically about 7 orders of magnitude fainter than the GNSS signals. Future work to demonstrate the high relative accuracy that D-VLBI is expected to yield must be performed in conjunction with nearby spacecraft with signal transmissions specifically designed for VLBI observations, in frequency and signal strength. We used simulations of D-VLBI and standard VLBI observations of Earth satellites to investigate how well the kinematic celestial reference frame can be tied to the dynamic satellite frames using spacecraft as frame ties. We found that standard VLBI observations can, in principle, deliver frame ties accurate at the 1 millimeter level given a suitably large number of observations to overcome typical statistical errors. Using the knowledge learned and tools developed for this project we have contributed to the development and planning of upcoming missions and mission proposals, and we are well prepared to continue carrying out D-VLBI research projects in the future.
Projektbezogene Publikationen (Auswahl)
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(2013): Processing SELENE Differential VLBI Data, Seventh General Meeting (GM2012) of the International VLBI Service for Geodesy and Astrometry (IVS), 4–9 March 2013, in Madrid, Spain, Behrend, D. & Baver, K.D. (Eds), National Aeronautics and Space Administration, pg. 291–295
Plank, L., Boehm, J., Madzak M., Tierno Ros, C., & Schuh, H.
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(2013): VLBI satellite tracking for the realization of frame ties. PhD thesis, Vienna University of Technology, Vienna
Plank, L.
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(2014): Precise station positions from VLBI observations to satellites: a simulation study. J Geod, Vol. 88 (7), 659-673
Plank L., Böhm J., Schuh H.
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(2015): Progress in determining ties between kinematic and dynamic reference frames through differential very long baseline interferometry, 26th IUGG General Assembly, Prague, Czech Republic
Anderson, J.M., Heinkelmann, R., Schuh, H.
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(2015): Software Development for D-VLBI Scheduling and Analysis of Spacecraft Observations, 22nd Meeting of the European VLBI Group for Geodesy and Astrometry, 17–21 May 2015, in Sao Miguel (Azores), Portugal
Anderson, J.M., Liu, L., Heinkelmann, R., Schuh, H., Baladakis, K., Glaser, G., Karbon, M., Lu, C., Mora-Diaz, J., Nilsson, T., Raposo-Pulido, V., Soia, B.
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(2017): GFZ Simulations of VLBI Observations of E-GRASP/Eratosthenes, 23rd European VLBI Group for Geodesy and Astrometry Working Meeting, 14-19 May 2017, Göteborg, Sweden
Anderson, J.M., Beyerle, G., Glaser S., Heinkelmann, R., Liu, L., Nilsson, T., Schuh, H.
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(2017): Observations of the APOD satellite with the AuScope VLBI network, 19th EGU General Assembly, EGU2017, 23-28 April, 2017, in Vienna, Austria., pg.14304
Hellerschmied, A., Plank, L., McCallum, J., Sun, J., Lovell, J., Böhm, J.
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(2017): VLBI observations of GNSS-satellites: from scheduling to analysis, Journal of Geodesy, Vol. 91, pg. 867-880
Plank, L., Hellerschmied, A., McCallum, J, Böhm, J., Lovell, J.
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(2018): Frame tie based on VLBI observations to near-field satellites, PhD thesis, Technical University of Berlin, Berlin
Liu, L.
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(2018): Simulations of VLBI observations of a geodetic satellite providing colocation in space, Journal of Geodesy, Vol. 92, pg.1023-1046
Anderson, J.M., Beyerle, G., Glaser, S., Liu, L., Männel, B., Nilsson, T., Heinkelmann, R., Schuh, H.
