GSFC VLBI Current Year News
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Guilhem Moreaux (CLS) made a presentation at the 2017 Fall AGU meeting:
"Analysis of the DORIS, GNSS, SLR, VLBI and gravimetric time
series at the GGOS core sites", by Guilhem Moreaux (CLS),
Frank Lemoine (GSFC 61A), Vincenza Luceri (E-GEOS), Erricos Pavlis (UMBC),
Dan MacMillan (GSFC 61A/NVI), Sylvain Bonvalot (IRD) and Jerome Saunier (IGN).
The presentation discussed initial analysis of time series from different
geodetic techniques at co-located GGOS sites. The goals were to evaluate the
level of agreement between the techniques and physical tie vectors and
to compare their spectral content. Horizontal site velocities showed
good agreement. Common annual signals are seen for several sites.
John Gipson gave a poster presentation at the 2017 Fall AGU meeting on the
"Ad Hoc Working Group on Diurnal and Semi-diurnal Earth Orientation Variation".
The working group is tasked with evaluating different models of EOP variation
and making recommendations to the IERS. The current IERS model is over
20 years old, and much has changed since then.
On December 14, 2017 John Gipson attended a workshop on the Terrestrial
Reference Frame Error Budget, and he gave a presentation on the error sources
in VLBI. A large error source is gravitational deformation of VLBI antennas.
This deformation changes the path length of the radio signal and results in a
change in the estimated up position. The magnitude of the effect can be up to
20 mm. Fortunately this deformation effect can be measured by a one-time
antenna survey that costs ~$25K. These surveys should be done to achieve
1 mm accuracy.
John Gipson attended the IERS directing board meeting in New Orleans on
December 10, 2017 as the IVS representative. He gave a presentation on the
activities of the IVS. He also discussed the work of the IERS working group
on sub-daily EOP variation, of which he is a chair. Gipson also
attended a meeting of the Bureau for Networks and Operations on December 14
and gave a summary of IVS activities.