Modeling thermal deformation of VLBI antennas with a new temperature model |
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| Authors: | Joerg Wresnik Rüdiger Haas Johannes Boehm Harald Schuh |
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| Institution: | 1. Institute of Geodesy and Geophysics (IGG), Vienna University of Technology, Gusshausstr. 27-29, 1040, Vienna, Austria
2. Onsala Space Observatory (OSO), Chalmers University of Technology, 412 96, G?teborg, Sweden
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| Abstract: | Temperature variations at very long baseline interferometry (VLBI) sites cause thermal deformations of the VLBI antennas and
corresponding displacements of the VLBI reference points. The thermal deformation effects typically contain seasonal and daily
signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending
on the design of the antenna structure, on the material, and on the environmental effects such as global station position,
station height and climatology effects. Simple methods to correct this effect use the difference of the environmental temperature
with respect to a defined reference temperature, the antenna dimensions, the elevation of the antenna, the material of antenna
structure. Applying these simple models for thermal deformation in the VLBI data analysis improves the baseline length repeatability
by 3.5%. A comparison of these simple models with local thermal deformation measurements at the antennas in Onsala and Wettzell
show that the local measurements and the modeled corrections agree well when the temperature of the antenna structure is used,
but agree less good when the surrounding air temperatures are used. To overcome this problem we present a method to model
temperature penetration into the antenna structures, that allows to model thermal deformation effects that agree with the
observed vertical deformation of the Onsala and Wettzell radio telescopes with a root mean square deviation of 0.07 and 0.13 mm,
respectively. Possible implementations in the VLBI analysis are presented, and the definition of an adequate reference temperature
is discussed. |
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| Keywords: | VLBI Thermal expansion Reference temperature Local tie |
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